Article

Predator perches: A visual search perspective

Wiley
Functional Ecology
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Abstract

Summary • Predators hunting by sight often search for prey from elevated perches or hovering positions above the prey habitat. Theory suggests that prey visibility depends strongly on predator perch height and distance, but their quantitative effects have not been experimentally tested in natural habitats. • We estimate for the first time how prey visibility depends on predator perch height, distance and vegetation height in an open natural habitat, based on visibility measurements of two targets: a mounted bird and a graduated plate, from five perch heights (0·2–8 m) and six distances (5–120 m). • For both targets, their proportion visible increases strongly with observer perch height and proximity. From the lowest perch, visibility of the target bird declines to • Models of predator search suggest that hunting success and predation rate depend strongly on the prey detection rate, which is expected to decline with distance r approximately as r−d. However, d, the distance decay parameter, has not previously been empirically estimated in natural predator habitats. For distance – prey visibility relationships similar to those observed here, we find a realistic estimate of d to be 2·1–2·4. • The results demonstrate the crucial role of relative perch and vegetation height for prey visibility, which is of relevance for habitat management. The strong increase of prey visibility with predator search height suggests that removal of predator perches can improve the survival of endangered prey populations in open habitats. Conversely, perch preservation or addition can improve habitat suitability for some predator species where perches are rare or lacking.

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... Previously, mortality caused by direct collisions with fences was one of the few identified risks fences pose to sage-grouse survival (Stevens et al., 2012, Jones, 2014, Van Lanen et al., 2017. Recent research, however, indicates a link between grazing related infrastructure, predator movement behavior, and survival of ground dwelling birds (Pedlar et al., 1997;Andersson, et al., 2009;Coates et al., 2016;Vold, 2018;Cutting et al., 2019). In grazing modified landscapes, predators may be able to use vertical-linear features to increase their foraging efficiency through increased search efficiency and handling time of prey (Harju et al., 2018). ...
... Avian nest predators (e.g., ravens) use fences to increase movements and foraging efficiency (Hovick et al., 2014;Coates et al., 2016). Ravens use vertical-linear features for perches that can improve visibility (Andersson et al., 2009). Coyotes in the eastern United States use habitat edges and fencerows between suburban and rural areas to increase their movements (Atwood et al., 2004). ...
... Higher elevation areas oftentimes have more trees which increase the number of perches for aerial nest predators. More perches in turn can increase sightability of nests (Andersson et al., 2009;Coates et al., 2016;Harju et al., 2018), a possible reason why the combined additive effects of fence type and elevation on nest survival did not vary between the two fence types at higher elevations. Coyotes on the other hand have lower successful prey capture attempts in more densely vegetated forested areas (Gese et al., 1996). ...
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Livestock grazing is the most common land-use practice in aridland ecosystems of the American West. Widespread and long-term declines of greater sage-grouse (Centrocercus urophasianus), an umbrella species for other sagebrush-associated vertebrates, has challenged land managers to find solutions to help bolster populations. Livestock grazing infrastructure (e.g., fences) among western rangelands are one potential factor impacting sage-grouse populations as nest survival-a key demographic rate that influences population size-can be 4x higher when placed >100 m away from the nearest fence. We implemented the first-ever long-term (8 years) and large-scale (70 km in length) management action designed to evaluate changes in nest survival related to fence modifications in the Centennial Valley of Montana, USA. Fence modifications included perch deterrents placed atop fence posts to reduce perching by avian nest predators. Additionally, the bottom fence wire was raised to 45 cm from the ground to reduce the funneling of mammalian predators along fences who are in search of carcasses from collisions and/or nests placed near fences. Using a Bayesian statistical framework, we found that fence modifications increased 28-day nest survival within 100 m of mitigated fences by an average of 10.6 % (85 % CRI: 3.7-24.9 %). The difference in survival between fence types was most pronounced for modified fences in low elevations, while modified fences resulted in higher survival rates throughout the nesting season. Our findings suggest that modifying fences designed to reduce the search efficiency of sage-grouse nest predators appear to benefit nest survival in sage-grouse. The highlighted fence modification technique offers practitioners a tool to advance grazing systems that reduce the impacts of grazing infrastructure on greater sage-grouse.
... However, the presence of artificial perches does not always result in their use by birds (Bohall and Collopy 1984). Research by Leyhe and Ritchison (2004) and Andersson et al. (2009) suggests that perch height, as well as vegetation height, affect a predator's perch choice because they alter prey vulnerability and capture success by predators. Furthermore, the addition of artificial perches can reduce the suitability of habitat for prey species because of their perceived risk of predation (Andersson 1980, Wallander et al. 2006. ...
... Given typical 2.4 m spacing of fence posts, average-sized core areas had over 4,500 individual fence posts relative to 24 distribution poles at standard 100m spacing. Therefore, although it is reasonable to assume hawks preferred taller perches when equally availability (Andersson et al. 2009), the importance of fence posts stands to reason because they were available among all habitat types within core areas. The fact that density of fence posts and its interaction with cropland were important at the home-range level indicated that increasing fence density moderated the effect of proportion of cropland on home-range size. ...
... My results demonstrate the importance of tame grasses (i.e., non-native grazed or hayed cover) at the home-range scale as they comprised ~25% of home ranges. It is likely that Ferruginous Hawks benefited from ranges with less dense, shorter vegetation with increased elevated perch options due to the improved foraging radius (Andersson et al. 2009) and ...
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Human alteration of the landscape can have implications for wildlife at the individual and population levels. The grassland ecosystem has been highly altered and is at risk of further alteration due to increasing demand for human food, pastureland, and energy development. The Ferruginous Hawk (Buteo regalis), a grassland obligate, has experienced declines across its range due to loss of habitat leading to its listing as a Threatened species in Canada. Understanding how breeding Ferruginous Hawks have been affected by anthropogenic change in the grassland region of southern Alberta and Saskatchewan is important to inform species recovery and management. My goal was to investigate how anthropogenic development has affected Ferruginous Hawk range use and perch choice at the level of 3rd-order selection. I tracked 48 breeding, male Ferruginous Hawks during the 2012-2017 breeding seasons, and used high-resolution satellite telemetry to address this goal. In Chapter 2, I measured the size of hawk core areas (50% contour; x̄ = 3.54 km2 ± 8.52 SD) and home ranges (95% contour; x̄ = 36.33 km2 ± 94.74 SD) (n = 92), the first range-size estimates for satellite-tracked Ferruginous Hawks in Canada. I used linear mixed models to test the relationship of perch density and land-cover type on range size as an indicator of range quality. I found the density of fencelines and proportion of cropland were significant influences on range quality, with higher densities of fenceline and lower proportions of cropland resulting in smaller core areas. However, at the home-range scale, there was a significant interaction between fenceline density and the proportion of cropland, with increasing densities of fenceline mediating the effect of proportion of cropland on home-range size. Additionally, increasing proportions of tame grass and tame hay resulted in smaller home ranges and thus higher range quality. In Chapter 3, I studied 24 hawks that were monitored intensively in 2013 and 2014 with GSM transmitters, which generated a high volume of location fixes. My objective was to evaluate perch use by Ferruginous Hawks at two scales. Firstly, I estimated Resource Utilization Functions at the home-range level to compare use intensity among elevated perch types (fencelines, power distribution lines, and power transmission towers), and also among common land-cover types (native grassland, cropland, tame grass, tame hay, and idle field). Resource Utilization Functions indicated that hawks showed the highest relative use at areas near transmission towers, but they were the least abundant elevated perch types on the landscape. Hawks also showed highest use in areas near distribution lines and areas far from fencelines. Among vegetated land-cover types and relative to areas with native grassland, hawks showed highest use in areas with low levels of cropland and high levels of tame grass and tame hay. Secondly, I visited 1,436 perches of known use, distributed among 20 hawk home ranges, and measured micro-site land-cover characteristics and relative prey abundance, indexed by mammal burrow counts, within the hypothetical viewscape (i.e., 50 m) of a perched hawk. I tested the influence of these predictors on intensity of perch use, with mixed effects logistic regression. Fence posts were the most common elevated perch type, comprising 52% of all perches. Transmission towers were the most heavily-used perch type but were the least abundant perch type on the landscape, resulting in less overall use. Hawks showed higher use at perches with higher proportions of bare ground, higher burrow counts, and less cropland within 50 m. I concluded that, although prey abundance is important for Ferruginous Hawks, prey accessibility and visibility, as influenced by the juxtaposition of perch height, amount of bare ground, and relative abundance of prey are the best indicators of perch use within home ranges. In Chapter 4, I summarize potential benefits and consequences related to human-made elevated perches on Ferruginous Hawks and recommend that future studies should investigate perch use of Ferruginous Hawks through direct observation and experimentation to determine how placement of new perches may affect breeding individuals.
... Further, our dietary analysis showed that for Whinchats soil-dwelling invertebrates tended to be of secondary importance as food because the majority of prey items ([70 % in each age class) were those associated with vegetation. This seems to imply indirectly the importance of a mosaic-like structure of the microhabitat with low vegetation or vegetation-free patches and bare ground, where prey are more accessible and the hunting of foraging Whinchats is more efficient (Bastian et al. 1994;Bastian and Bastian 1996;Andersson et al. 2009). Lastly, we were able to identify some invertebrate prey items only to the level of class/order (such as Araneae or Lepidoptera larvae), which to some degree hampered a more detailed analysis and the drawing of further inferences. ...
... Consequently, owing to the lack of the compact layer of vegetation normally occurring in grasslands, the soil on abandoned farmland was drier. Presumably this is beneficial for some soil-dwelling invertebrates, such as ants, some coleopterans and orthopterans (which are abundant in the diet of the nestling Whinchats we examined), which are also easier to catch on bare ground or in lower vegetation (Andersson et al. 2009;Schaub et al. 2010). In addition, it should be stressed that Whinchats hunt primarily from a perch, so both the denser vegetation (i.e. more concealed prey) and the perch height (or even the lack of perches in modern grasslands) are of critical importance for access to prey and hunting efficiency (Andersson 1981;Andersson et al. 2009). ...
... Presumably this is beneficial for some soil-dwelling invertebrates, such as ants, some coleopterans and orthopterans (which are abundant in the diet of the nestling Whinchats we examined), which are also easier to catch on bare ground or in lower vegetation (Andersson et al. 2009;Schaub et al. 2010). In addition, it should be stressed that Whinchats hunt primarily from a perch, so both the denser vegetation (i.e. more concealed prey) and the perch height (or even the lack of perches in modern grasslands) are of critical importance for access to prey and hunting efficiency (Andersson 1981;Andersson et al. 2009). This concurs with the assumption that the mobility of ground-foraging insectivorous passerines and access to food are of greater importance during the selection of a foraging site than the abundance of food per se, which translates into preferential foraging in short vegetation, even though more invertebrate prey were available in tall vegetation (discussed in van Oosten et al. 2014;Schaub et al. 2010). ...
Article
Direct observational studies are needed to address dietary adjustment in species breeding in isolated non-forest habitat islands with respect to the energy demands of growing nestlings and breeding patch size. Using new dietary records determined for nestlings of Whinchat Saxicola rubetra, a dramatically declining insectivorous passerine and an indicator species of the cessation of agricultural activity, we investigated the relationships between changes in the main dietary characteristics, numerical and biomass contributions of major taxonomic and functional prey groups (expressing chitin content, vertical distribution, habitat preference and vagility within the landscape) and brood age, nestling condition and size of abandoned fields (i.e., breeding patches). Broods from larger abandoned fields received more sedentary and heavier prey like Orthoptera and soil-dwelling invertebrates, whereas the proportion of caterpillars, aerial insects and prey from vegetation decreased with increasing patch size. Nestling condition was positively correlated with the proportion of caterpillars and Orthoptera or sedentary prey taxa, but negatively with the proportion of Coleoptera or vagile prey taxa in the diet, though not with patch area. This suggests that parent Whinchats can overcome the habitat constraints resulting from the small area of an abandoned field by interchangeably incorporating the two major prey groups (Orthoptera or Lepidoptera) into the diet they feed to their nestlings. This implies a continuum in dietary optimization that is a trade-off between a brood's nutritional demands and the parents' ability to deliver top-ranked invertebrates present mostly within the breeding patch.
... Reductions in shrub and grass cover associated with juniper expansion may increase the susceptibility of small mammals to predation because of reductions in cover and the availability of preferred food (Coultrap et al. 2008). The presence of juniper may also increase the hunting efficiency of avian predators by providing perches (Andersson et al. 2009, Coates et al. 2014, Severson et al. 2017. Cheatgrass can reduce survival of small mammals, an effect ameliorated by the presence of native shrubs (Ceradini and Chalfoun 2017). ...
... We included annual and native grass covers and shrub cover as covariates. We also evaluated the effect of juniper cover on home-range size because juniper may lead to reduced movement through increases in perceived or actual predation risk if avian predators use juniper as hunting perches (Andersson et al. 2009). Finally, we included the percent cover of rocky areas because rocky areas may provide escape cover for small mammals while increasing the distances that animals need to travel to access food (Melaschenko and Hodges 2020). ...
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Invasion and expansion of non‐native and native plants have altered vegetation structure in many terrestrial ecosystems. Small mammals influence multiple ecosystem processes through their roles as ecosystem engineers, predators, and prey, and changes to vegetation structure can affect habitat use, community composition, and predator‐prey interactions for this assemblage of wildlife. In the sagebrush ( Artemisia spp.) shrublands of the western United States, invasion by non‐native grasses and expansion of native conifer trees beyond their historical range has altered vegetation structure. These changes may potentially affect distributions and interactions of deer mice ( Peromyscus maniculatus ), which are generalist omnivores, and Columbia Plateau pocket mice ( Perognathus parvus ), more specialized granivores. To assess the extent to which altered habitat affects small‐mammal density, survival, and home‐range size, we examined these aspects of small‐mammal ecology along a gradient of cheatgrass ( Bromus tectorum ) invasion and western juniper ( Juniperus occidentalis ) establishment in sagebrush shrublands in southwestern Idaho, USA. From 2017–2019, we used a spatially explicit mark‐recapture design to examine attributes of small‐mammal ecology along an invasion gradient. We did not find support for an effect of cheatgrass cover on density or survival of either species. Home‐range size of deer mice was 2.3 times smaller in heavier cheatgrass cover (60%) compared to areas with little or no cheatgrass cover. Density of deer mice was highest (5 individuals/ha) in areas with 10% juniper cover and decreased with increasing juniper cover, whereas density of pocket mice was positively influenced by shrub cover. Survival of deer mice declined as juniper stem density increased. Conversely, survival of pocket mice increased with increasing juniper stem density. We found evidence for interspecific interactions between these 2 species, in the form of a density‐dependent effect of deer mice on pocket mouse home‐range size. Home‐range size for pocket mice was 2 times smaller in areas with the highest estimated density of deer mice compared to areas with low densities of deer mice. Our data provides unique information about how small mammals in the sagebrush steppe are affected by expanding and invasive plant species and potential ways that habitat restoration efforts, in the form of conifer removal, may influence small mammals. Understanding the response of small mammals to conifer expansion or removal may shed light on the demographic and numerical responses of other wildlife associated with the sagebrush biome, including predators.
... Secondly, the presence of nearby large forest patches might provide high availability of natural nesting sites, with the result that the artificial nest-boxes and baskets were less attractive to breeding raptors. Further, the design, height and spacing of the nest-boxes and perches might have influenced their usage by raptors -e.g., preference of features of the artificial elements may be species-specific and prey visibility increases with height of raptor perch (Kay et al., 1994;Andersson et al., 2009;Peisley et al., 2017). Similarly, the location of the artificial perches near the vineyard edges, where natural or semi-natural woody vegetation surrounding the vineyard provides suitable perching spots (i.e., trees and shrubs), may have deterred raptors from using the artificial perches. ...
... A more complex perch design should be implemented where raptors can hide and make a quick attack on their prey. Similarly, attaching a horizontal extension or platform to the poles to facilitate raptor's perching (e.g., Peisley et al., 2017) may increase the use of these perches by raptors and increasing the height of perches could encourage their use and hunting efficiency (Andersson et al., 2009;Wong and Kross, 2018). A longer study might be needed to evaluate the effectiveness of the installed artificial elements and to identify potential trends or patterns that might not be evident in shorter-term investigations. ...
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Several bird species may cause serious damage to grape production. The ability of raptors as biological control agents of grape-eating birds is poorly understood and under-used. We installed artificial nests and perches to encourage the presence and activity of raptors in vineyards located in central Spain and explored their effectiveness to reduce damage to grapes. We characterized the raptor community by field surveys and assessment of natural breeding sites, evaluated the abundance of grape-eating birds, and sampled damage to grape production for three consecutive years. Raptor community in the study area was diverse (13 species). Breeding of ornitophagous species such as Booted eagle Hieraaetus pennatus and Northern goshawk Accipiter gentilis was confirmed in the forest patches. We identified 10 grape-eating bird species, with Spotless starling (Sturnus unicolor) being the most abundant. Distance from the edges between vineyards and natural and semi-natural woody vegetation affected damage to grapes, with more damage close to the edges. The installed elements did not significantly reduce damage to grapes. Woody vegetation in and around the vineyards may reduce the success of the installed elements by providing shelter to grape-eating birds and suitable sites for raptor breeding and perching. Other variables such as vine orientation, land-cover, and distance to raptor nests did not affect damage to grapes. To promote the conservation of raptors and their regulating services in this Mediterranean agroforestry system, more research is needed to find methods to increase the presence of raptors in vineyards and to manage the woody shelters used by grape-eating birds around crops.
... The relationship between organisms and the environment is an important topic in ecology, such as in habitat use and mediating interspecific relationships. [5][6][7][8] Previous study based on Geographic Information System (GIS) to analyze remote sensing images in Serengeti National Park has found that lions (Panthera leo) tend to choose habitats with better hiding for themselves, rather than the area with more prey. 9 However, limited by the 2D properties of remote sensing images, it is difficult to verify them in complex forest ecosystems. ...
... For example, studies on predator perches show that prey visibility increases with perch height in open habitats. 7 African wild dogs (Lycaon pictus) choose relief terrain to avoid lions and lessen their risk of predation. 8 These studies qualitatively discussed the effect of the shielding effect of the environment on the study objects. ...
Article
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The development of ‘three-dimensional ecology’ reveals refreshing phenomena and challenges us to use three-dimensional information for studying animal perception. We created a new processing framework to quantify the shielding effect using a reconstructed environmental structure. The framework achieves three objectives: 1) the observed is introduced, 2) the observed space size can be flexibly dealt with, and 3) three-dimensional attributes are assigned to the environmental structure. Our processing framework is an applicable method to ‘three-dimensional ecology’ based on the three-dimensional attributes of physical structures. We advocate for greater emphasis on ‘three-dimensional ecology’ to recreate realistic animal living conditions and better reveal their behaviors.
... Birds use electric infrastructure present in their environments (Andersson et al. 2009, Lehman et al. 2007. But this is neither safe for birds (APLIC 2006, Tintó et al. 2010) nor for the electric system (Lammers and Collopy 2007). ...
... Different strategies allow raptors to improve their chances of prey detection and capture under certain ecological conditions (O'Rourke et al. 2010). The predators amongst these species tend to hunt by sight, searching for prey from elevated perches or hovering positions above the prey's habitat (Andersson et al. 2009). The availability of perches can facilitate and increase hunting efficiency due to higher visibility and less energy expenditure than hovering (Fleming and Bateman 2018). ...
Article
Avian species often take advantage of human-made structures, such as perching on power poles, although this can lead to negative effects for both birds and infrastructure. It has been demonstrated that anchor-type pylons, with strain insulators, are amongst the most dangerous of these structures. Our goal was to develop a methodological approach to evaluate the ways in which raptors perch on the six most commonly used strain insulator configurations in Spain, and to build a risk index that can be used to prioritise them. To study the ways raptors perch, we worked with six wildlife rescue centres in central Spain for almost a year assessing these six strain insulator configurations in 83 perch trials with 176 raptors in ample flying pens. We analysed 475 complete survey days, with an approximate number of 258,960 analysed pictures, including 6,766 perchings on strain insulators. We assessed the influential factors for these 6,766 perchings and developed a novel approach to prioritise strain insulator configurations that can be used anywhere. Our results suggest that longer insulator strains (i.e. PECA-1000 and Caon-C3670) are the safest, according to our prioritization criteria, although these results require further assessment in the field. Managers and conservationists should take into account these results to improve management and conservation actions.
... The third scenario is to erect artificial perches for birds of prey (e.g. buzzards) (Andersson, Wallander, & Isaksson, 2009;Kay, Twigg, Nicol, & Korn, 1994). Finally, the fourth scenario is to combine hedgerows and perches so as to favor predation by birds and mammals alike. ...
... It should be noted that all these comparisons might vary with the cost values assigned to the land-use categories, and to the spatial representation of specific actions such as the erection of perches. Here, perches were featured by 20 m-radius discs to represent the area subjected to intense predation as observed in Andersson et al. (2009). But those authors report that this area depends both on the height of the perches and on visibility conditions. ...
Article
Patch-based graphs are widely used to display and quantify landscape connectivity. They are specially relevant for decision support in land planning and biological conservation. Matching connectivity analyses with practical actions in agricultural landscapes involves considering management units rather than habitat patches. However, at a local scale, the classical method for prioritizing graph elements (node removal) using connectivity indexes such as delta IIC could be viewed as a highly contrived approach with respect to the actual changes in land use. Here we address the relevance of this method compared to simulations likely to display these land-use changes in a more realistic way. Prioritization as determined by the removal method is tested here against simulated land-use changes in four scenarios (e.g. replacing grasslands by croplands) for an agricultural area in the Jura massif (eastern France) where field actions are undertaken to combat the spread of grassland rodents. The results obtained by ranking all the parcels ("enumerative" approach) show that the removal method provides rankings similar to those obtained with the land-use change scenarios, except for the planting of hedgerows. However, defining a limited number of key parcels ("cumulative" approach) results in different rankings whatever the scenarios. This shows that when applying parcel-based graphs to practical actions, the reliability of the removal method depends on the way the connectivity analysis is conducted. Simulating land-use changes, which is more realistic but more time-consuming, proves relevant if only a few key parcels need to be identified for actions to be conducted in the field.
... Owls selected and showed increased use of both fence lines and posts, indicating predator vigilance is a priority for male owls during the day. Fences and posts in this study were of a similar height (~1.25 m tall) and likely used by the owls as perches to increase their field of vision (Andersson et al. 2009) and maximize detection of predators. Increased visual detection should shorten response time (Devereux et al. 2006) and therefore increase the probability of successfully reacting to a threat (Kenward 1978, Fitz gibbon 1990, Krause & Godin 1996. ...
... Though only available to a small portion of our sample of owls, perches > 2 m tall (power lines and tall shrubs) were not used by any individuals. Larger raptors such as hawks prefer taller perches (Bohall & Collopy 1984, Berkelman et al. 2002, Leyhe & Ritchison 2004 because of increased prey visibility (Andersson et al. 2009). Increased risk from other raptors is the most likely reason why burrowing owls do not use these taller perches. ...
Article
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Artificial sensory disturbances (sound and light) can extend far beyond the physical footprint of human development. Nocturnal predators such as owls may be influenced by artificial sound and light, as they depend on aural and visual cues when hunting. Owl nocturnal movements may also be altered by physical changes to the landscape, as these can affect prey availability. The burrowing owl population in Canada has declined by 90% and was classified as endangered in 1995. We tracked adult male burrowing owls Athene cunicularia with GPS dataloggers, and used resource selection models to examine their night-time movement patterns in relation to human infrastructure and associated artificial light and sound. The amount of sound and light from compressor stations, oil wells, traffic, towns and buildings was calculated for each owl and random location. We found that owl night-time space use was better predicted by distance to infrastructure on the landscape than by intensity of sensory disturbance. Burrowing owls did not show a pronounced avoidance of artificial sound. Infrastructure best predicts owl space use, perhaps because associated changes to vegetation alter prey abundance and availability. While human infrastructure most influenced owl nocturnal space use, the extent to which ecosystems are impacted by artificial sound and light is becoming clearer and needs to be considered when assessing the total effect of human development on species.
... Wildfire increases predation risk by reducing visual screening cover. Juniper expansion may potentially increase the number or success rate of avian predators by providing vertical substrates used for nesting and perching (Andersson et al. 2009;Coates et al. 2014;Severson et al. 2017) and induces riskier movements in areas where juniper is intermixed with sagebrush, leaving sage-grouse vulnerable to visually acute predators . Long-distance movements during the breeding season have been linked to decreased survival (Cross et al. 2017;Ebonhoch et al. 2019), and increased space use during the breeding season was linked to higher stress as measured by corticosterone concentrations (Rabon et al. 2021). ...
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Context Landscape composition and configuration are essential factors for species distribution and persistence. Disturbance changes landscapes and can impact individuals' movement and space use based on mobility with tradeoffs between resource acquisition and survival. Objectives We evaluated how spring space use and survival of female sage-grouse varied depending on the composition and configuration of disturbances within sagebrush and non-sagebrush dominated habitats, and whether the size of spring neighborhoods affected survival. Methods We created annual spring neighborhoods for individual female sage-grouse using location data from GPS-marked birds. We calculated the proportion, clumpiness, and interspersion and juxtaposition index (IJI) for each cover class within each neighborhood. We used linear mixed and Cox proportional hazards models to examine the interactive effects of composition and configuration on the area of space use and cumulative survival. Results Spring neighborhood size decreased when the proportion and interspersion of non-sagebrush and sagebrush cover was high but increased when interspersion was low. Neighborhood size decreased when interspersion and proportion of anthropogenic footprint was high but increased when proportion was low. Sage-grouse survival decreased as the proportion of anthropogenic footprint increased, regardless of configuration. Survival decreased when the proportion of juniper cover was high, and interspersion was moderate. Females that spent more time on nest had smaller neighborhood sizes and were more likely to survive during the spring season. However, there was no effect of neighborhood size on survival. Conclusions Our results indicate that heterogeneity of habitat and disturbance reduces spring neighborhood size and decreases spring survival of female sage-grouse. These results suggest that management actions should focus on reducing pinyon-juniper where interspersion is high and reducing or removing anthropogenic disturbance near sage-grouse breeding areas.
... Fences are also linear foraging routes (Boone & Hobbs 2004), providing perches for forest-nesting raptors such as Common Buzzard Buteo buteo (Cieśluk et al. 2023), which could increase predation risk of broods moving across the country. The effect of fences, through the provision of perches, is particularly relevant in open landscapes (Andersson et al. 2009). ...
... For example, relief features can act as barriers (e.g., a large river) or corridors (e.g., a valley in a mountain range) that influence the movement paths of animals and provide protection from predators (e.g., cliffs and caves as breeding and nesting grounds for birds and bats; Bouchet et al., 2015;Gordon et al., 2022). Furthermore, terrain characteristics and specific relief features can determine hunting success, for example by providing cover for stalking predators, slowing down prey or providing a physical barrier against which they can corner their prey (Andersson et al., 2009;Bouchet et al., 2015). Conspicuous relief features also attract animals to use them for scent-marking and thus function as communication hubs that help maintain socio-spatial organisation of populations Melzheimer et al., 2020). ...
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Geodiversity, encompassing various geophysical elements, can have an important impact on species distribution and affect animal behaviour patterns. Although many wild felids are attracted to rugged terrain and conspicuous relief features, most previous research was limited to general topographical characteristics (e.g., slope or terrain ruggedness) and rarely considered the effects of specific microhabitat characteristics. This gap is primarily due to the limited availability of high-resolution digital terrain models (DTMs) and relief features data at larger scales. However, LiDAR DTMs can be used in combination with various automatic methods to detect relief features, enabling non-contact and accurate mapping of large, remote and densely-forested areas. Here, we investigated the selection patterns of various karstic relief features, as well as topographic, anthropogenic and vegetation characteristics, by two sympatric felids, the Eurasian lynx (Lynx lynx) and the European wildcat (Felis silvestris), in the Dinaric Mountains, Slovenia. We used LiDAR DTMs to calculate topographic characteristics and detect karst relief features based on automatic methods. We compared the selection of these features between the GPS-collared lynx and wildcats under a use-availability approach. We also investigated the differences in the selection of these features by lynx based on their origin and experience (remnant vs. translocated and naive vs. experienced, respectively). We observed significant impact of relief features on space use by both felids and detected distinct selection patterns between the two species. Lynx selected rugged terrain and proximity of caves, cliffs, karst depressions, ridges, small rocky outcrops, and roads, but avoided human settlements and forest edges. Wildcats selected areas with lower surface slope, closer to main roads, forest edges, caves and ridges, but avoided cliffs, forest roads and human settlements. We observed stronger selection/avoidance patterns among the translocated compared to the remnant lynx, while the differences in experience levels were less important. Our study demonstrates the potential of integrating remote sensing techniques and information on geodiversity into the study of animal spatial ecology. Furthermore, our results indicate that specific relief features provide important abiotic microhabitats for felids and may influence habitat segregation between sympatric species. Our findings provide further evidence for the importance of geodiversity conservation and the need to incorporate abiotic microhabitat features in wildlife habitat selection studies.
... Increased predator densities could be driven by biotic factors, such as an increase in prey resources other than frogs. Increased detectability could be driven by abiotic factors, for example, a more open structural microhabitat which allows for more rapid detection of frogs, particularly by avian predators (Andersson et al. 2009). Alternatively, populations of co-mimic species may be at higher densities in these localities, ultimately allowing for accelerated predator learning (Allen and Greenwood 1988;Endler and Greenwood 1988). ...
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Geographic variation in natural selection derived from biotic sources is an important driver of trait evolution. The evolution of Müllerian mimicry is governed by dual biotic forces of frequency-dependent predator selection and densities of prey populations consisting of conspecifics or congeners. Difficulties in quantifying these biotic forces can lead to difficulties in delimiting and studying phenomena such as mimicry evolution. We explore the spatial distribution of morphotypes and identify areas of high mimetic selection using a novel combination of methods to generate maps of mimetic phenotype prevalence in Ranitomeya poison frogs, a group of frogs characterized by great phenotypic variation and multiple putative Müllerian mimic pairs. We categorized representative populations of all species into four major recurring color patterns observed in Ranitomeya: striped, spotted, redhead, and banded morphs. We calculated rates of phenotypic evolution for each of the 4 morphs separately and generated ecological niche models (ENMs) for all species. We then split our species-level ENMs on the basis of intraspecific variation in color pattern categorization, and weighted ENM layers by relative evolutionary rate to produce mimicry maps. Our phenotypic evolutionary rate analyses identified multiple significant shifts in rates of evolution for the spotted, redhead, and banded phenotypes. Our mimicry maps successfully identify all suspected and known areas of Müllerian mimicry selection in Ranitomeya from the literature and show geographic areas with a gradient of suitability for Müllerian mimicry surrounding mimic hotspots. This approach offers an effective hypothesis generation method for studying traits that are tied to geography by explicitly connecting evolutionary patterns of traits to trends in their geographic distribution, particularly in situations where there are unknowns about drivers of trait evolution.
... Carrion crows [Corvus corone]), which may result in enhanced nest predation (Andersson et al. 2009). ...
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Agricultural intensification and abandonment have led to a dramatic decrease of semi-natural grasslands such as low-intensity pastures and hay meadows. The Short-eared owl (Asio flammeus) is a ground-nesting raptor of open grasslands that has severely suffered from these changes. We studied the habitat preferences of this umbrella species of open grasslands in its last permanent breeding area in Germany (East Frisian Islands, southern North Sea). We analysed the breeding-territory preferences based on 576 territories on six of the islands. Moreover, we assessed nest-site preferences of 13 breeding pairs on the German abundance hotspot, the island of Spiekeroog. Our investigation revealed that the Short-eared owl strongly preferred open dunes for breeding, especially dune grasslands. By contrast, built-up areas and small stands of trees were avoided. For nest-building, microhabitats with a high cover of the herb layer and litter resulting in tall vegetation were favoured. By contrast, the vegetation in the wider surrounding of the nest was characterised by more bare ground and shorter vegetation but still a high cover of the herb layer and litter. In conclusion, our study highlights the prime importance of extensive open grasslands with a pronounced litter layer and largely lacking human disturbance as breeding habitats for the Short-eared owl. At the nesting site, we suggest that tall and dense vegetation with a high cover of litter (i) might enhance concealment and (ii) causes a favourable microclimate by protecting fledglings against adverse weather conditions. In the wider surrounding of the nest, shorter vegetation with a pronounced litter layer (i) improves fledgling mobility, (ii) fosters vole abundance and (iii) increases prey accessibility.
... In addition, some species prefer higher canopy closer to the forest edge for predation such as eagles, dollar birds, hornbill and falconet. These species prefer taller trees as a lookout for prey (Andersson et al. 2009). During observation, black hornbill was spotted feeding on beetles on the top of tall trees in RP. ...
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It is well established that oil palm is one of the most efficient and productive oil crops. However, oil palm agriculture is also one of the threats to tropical biodiversity. This study aims to investigate how set-aside areas in an oil palm plantation affect bird biodiversity. The research area includes two set-asides areas: peat swamp forest and riparian reserves and two oil palm sites adjacent to reserved forest sites. A total of 3,074 birds comprising 100 species from 34 families were observed in an oil palm plantation landscape on peatland located in the northern part of Borneo, Sarawak, Malaysia. Results showed that efforts by set-asides forest areas in large scale of oil palm dominated landscapes supported distinct bird species richness. High percentage of the canopies and shrub covers had a positive effect on bird species richness at area between oil palm and peat swamp forest. Herbaceous cover with height less than 1 m influenced the abundance of birds in the plantation closed to the peat swamp forest. The set-aside areas in oil palm plantations are essential in supporting bird’s refuges and should be part of oil palm landscape management to improve biodiversity conservation. Thus, provided the forest set-aside areas are large enough and risks to biodiversity and habitat are successfully managed, oil palm can play an important role in biodiversity conservation.
... Therefore, their presence increases near open grass and bare soil fields where they could be foraging for these valuable resources. Another advantage of open habitats is the early detection of predators since few structures obscure their vision [91]. As corvids are relatively heavy birds, they require longer to flee from approaching predators, so early detection of predators may be valuable [92]. ...
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Understanding habitat and spatial overlap in sympatric species of urban areas would aid in predicting species and community modifications in response to global change. Habitat overlap has been widely investigated for specialist species but neglected for generalists living in urban settings. Many corvid species are generalists and are adapted to urban areas. This work aimed to determine the urban habitat requirements and spatial overlap of five corvid species in sixteen European cities during the breeding season. All five studied corvid species had high overlap in their habitat selection while still having particular tendencies. We found three species, the Carrion/Hooded Crow, Rook, and Eurasian Magpie, selected open habitats. The Western Jackdaw avoided areas with bare soil cover,and the Eurasian Jay chose more forested areas. The species with similar habitat selection also had congruent spatial distributions. Our results indicate that although the corvids had some tendencies regarding habitat selection, as generalists, they still tolerated a wide range of urban habitats, which resulted in high overlap in their habitat niches and spatial distributions.
... Due to the structure of the canopy layer, PSF and RP attracted forest bird species such as trogons, iora, barbet and broadbills and arboreal birds such as pigeons and bee-eater. In addition, some species prefer higher canopy closer to the forest edge for predator birds as they prefer taller trees to lookout for prey (Andersson et al., 2009). Furthermore, the canopy of the PSF provides sufficient sunlight and space for the development of shrub layers such as lianas, epiphytes and hemiepiphytes which may attract forest birds that utilize the different vegetation strata (Hawa et al., 2016). ...
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It is a great privilege for us to present the authors and delegates of the conference with the proceedings of the inaugural International Conference on Food and Industrial Crops (ICFIC2022). We hope that you will find it informative, exciting and motivating. This version of e-proceeding contains a total of 28 papers submitted to the ICFIC2022 delivering the sustainable development of food and industrial crops in Malaysia and around the globe, concerning both crop-oriented and bio-based materials, which was held at The Waterfront Hotel, Kuching, Sarawak, Malaysia on 21st – 24th September 2022. This conference was one of the three concurrent international conferences under the umbrella of Congress on Sustainable Agriculture and Food Security (COSAFS2022). The conference was jointly organised by the Faculty of Agricultural and Forestry Sciences, Institute of Ecosystem Science Borneo, Universiti Putra Malaysia Bintulu Sarawak Campus and Ministry of Food Industry, Commodity, and Regional Development Sarawak (M-FICORD). The conference under the COSAFS2022 aims to provide a platform to discuss and exchange knowledge between participants, promote and strengthen international and national collaborations in sustainable agriculture and food security as well as identifying and promoting smart agriculture solutions for the development of sustainable agriculture and food security. Hopefully, this event will also spark innovative ideas, and foster research relations or partnerships between the various institutions, corporate bodies, and communities. The conferences featured more than 300 participants including academicians, research scientists, policymakers, and officials from public and private sectors with thought-provoking keynote lectures, oral and poster presentations in the field of sustainable agriculture and food security. The editors hope that this publication of e-proceeding will provide the reader with a broad overview of the latest research, development, and innovations and that it will be a valuable reference source for further research all over the world. The editors would like to express their sincere appreciation and thanks to all the authors for their contributions to this publication. We would like to express our utmost gratitude and appreciation to all the reviewers for their constructive comments on the papers. Nonetheless, we would also like to extend our special thanks to the organising team of COSAFS2022 who have work hard to ensure the success of the congress. Thank you.
... Construction, industrial activities, infrastructure, and vehicle traffic associated with oil development can cause direct mortality of grassland songbirds (Northrup and Wittemyer 2013), or indirectly increase their predation risk (Andersson et al. 2009;Campos et al. 2009). Noise from oil extraction can simultaneously decrease an individual's ability to detect predators or identify the presence of conspecifics. ...
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Oil extraction may impact wildlife by altering habitat suitability and affecting stress levels and behavior of individuals, but it can be challenging to disentangle the impacts of infrastructure itself on wildlife from associated noise and human activity at well sites. We evaluated whether the demographic distribution and corticosterone levels of three grassland passerine species (Chestnut-collared Longspur, Calcarius ornatus; Baird’s Sparrow, Centronyx bairdii; and Savannah Sparrow Passerculus sandwichensis) were impacted by oil development in southern Alberta, Canada. We used a landscape-scale oil well noise-playback experiment to evaluate whether impacts of wells were caused by noise. Surprisingly, higher-quality female Chestnut-collared Longspurs tended to nest closer to oil wells, while higher-quality Savannah Sparrows generally avoided nesting sites impacted by oil wells. Corticosterone levels in all species varied with the presence of oil development (oil wells, noise, or roads), but the magnitude and direction of the response was species and stimulus specific. While we detected numerous impacts of physical infrastructure on stress physiology and spatial demographic patterns, few of these resulted from noise. However, all three species in this study responded to at least one disturbance associated with oil development, so to conserve the grassland songbird community, both the presence of physical infrastructure and anthropogenic noise should be mitigated.
... Construction, industrial activities, infrastructure, and vehicle traffic associated with oil development can cause direct mortality of grassland songbirds (Northrup and Wittemyer 2013), or indirectly increase their predation risk (Andersson et al. 2009;Campos et al. 2009). Noise from oil extraction can simultaneously decrease an individual's ability to detect predators or identify the presence of conspecifics. ...
Article
Oil extraction may impact wildlife by altering habitat suitability and affecting stress levels and behavior of individuals, but it can be challenging to disentangle the impacts of infrastructure itself on wildlife from associated noise and human activity at well sites. We evaluated whether the demographic distribution and corticosterone levels of three grassland passerine species (Chestnut-collared Longspur, Calcarius ornatus; Baird's Sparrow, Centronyx bairdii; and Savannah Sparrow Passerculus sandwichensis) were impacted by oil development in southern Alberta, Canada. We used a landscape-scale oil well noise-playback experiment to evaluate whether impacts of wells were caused by noise. Surprisingly, higher-quality female Chestnut-collared Longspurs tended to nest closer to oil wells, while higher-quality Savannah Sparrows generally avoided nesting sites impacted by oil wells. Corticosterone levels in all species varied with the presence of oil development (oil wells, noise, or roads), but the magnitude and direction of the response was species and stimulus specific. While we detected numerous impacts of physical infrastructure on stress physiology and spatial demographic patterns, few of these resulted from noise. However, all three species in this study responded to at least one disturbance associated with oil development, so to conserve the grassland songbird community, both the presence of physical infrastructure and anthropogenic noise should be mitigated.
... For prey species, visual information from the environment can affect their ability to remain hidden or to detect approaching predators, thereby avoiding predation (Camp et al., 2012;Embar et al., 2011;Lima & Dill, 1990). On the other hand, predators relying on the vision for hunting can locate their prey and use appropriate predation strategies that increase their chance of success (Andersson et al., 2009;Hopcraft et al., 2005;Loarie et al., 2013). ...
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Visibility (viewshed) plays a significant and diverse role in animals' behaviour and fitness. Understanding how visibility influences animal behaviour requires the measurement of habitat visibility at spatial scales commensurate to individual animal choices. However, measuring habitat visibility at a fine spatial scale over a landscape is a challenge, particularly in highly heterogeneous landscapes (e.g. forests). As a result, our ability to model the influence of fine‐scale visibility on animal behaviour has been impeded or limited. In this study, we demonstrate the application of the concept of three‐dimensional (3D) cumulative viewshed in the study of animal spatial behaviour at a landscape level. Specifically, we employed a newly described approach that combines terrestrial and airborne light detection and ranging (LiDAR) to measure fine‐scale habitat visibility (3D cumulative viewshed) on a continuous scale in forested landscapes. We applied the LiDAR‐derived visibility to investigate how visibility in forests affects the summer habitat selection and the movement of 20 GPS‐collared female red deer Cervus elaphus in a temperate forest in Germany. We used integrated step selection analysis to determine whether red deer show any preference for fine‐scale habitat visibility and whether visibility is related to the rate of movement of red deer. We found that red deer selected intermediate habitat visibility. Their preferred level of visibility during the day was substantially lower than that of night and twilight, whereas the preference was not significantly different between night and twilight. In addition, red deer moved faster in high‐visibility areas, possibly mainly to avoid predation and anthropogenic risk. Furthermore, red deer moved most rapidly between locations in the twilight. For the first time, the preference for intermediate habitat visibility and the adaption of movement rate to fine‐scale visibility by a forest‐dwelling ungulate species at a landscape scale was revealed. The LiDAR technique used in this study offers fine‐scale habitat visibility at the landscape level in forest ecosystems, which would be of broader interest in the fields of animal ecology and behaviour.
... Our study contributes to the weight of the evidence demonstrating the extent of this ongoing threat to sage-grouse and other sagebrush obligate species Holmes et al. 2017). Conifer encroachment may impact sage-grouse productivity via several mechanisms including by increasing predation risk to nests, chicks, and adults (Andersson et al., 2009;Dinkins et al., 2014;Coates et al., 2017;Severson et al., 2017d;Olsen et al., 2021a), reducing soil moisture availability, (Roundy et al., 2014;Kormos et al., 2017), changing the overall canopy structure of Sagebrush ecosystems, and limiting herbaceous layer productivity (Miller et al., 2005;Severson et al., 2017a). Sage-grouse avoid conifer cover (Atamian et al., 2010;Casazza et al., 2011;Baruch-Mordo et al., 2013;Severson et al., 2017b;Picardi et al., 2020), but quickly recolonized nesting habitat following conifer removal in Oregon (Severson et al., 2017c;Olsen et al., 2021b) and Utah (Sandford et al., 2015, Sandford et al., 2017. ...
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Anticipating and mitigating the effects climate change will have on wildlife populations requires an improved understanding of the ways in which those populations are currently adapted to climate and how they are affected by variation in weather conditions. We used over 70,000 greater sage-grouse (Centrocercus urophasianus) wings, derived from hunter harvest in three western states, to characterize spatiotemporal variation in sage-grouse productivity throughout the North American Great Basin during 1993-2020. We then tested the hypothesis that previously-identified associations between precipitation and sage-grouse productivity are mediated by the availability of mesic habitats, which provide the diet resources required by broods during typical late-summer seasonal drought. We used random forest regression to model sage-grouse productivity as a function of mesic habitat availability (defined as those areas with maximum Normalized Difference Vegetation Index (NDVI) ≥0.3) during the late brood-rearing period, the more general effect of annual precipitation, and landcover composition. We also evaluated potential acute direct effects of exposure to inclement weather on sage-grouse productivity. Finally, we examined which weather and topographic variables best predict mesic habitat availability. We found the predicted positive relationship between mesic habitat availability and sage-grouse productivity, but annual precipitation explained additional variation in productivity even after accounting for mesic habitat availability. Hence, precipitation and drought may drive sage-grouse productivity via more than one mechanism acting on multiple demographic rates. Productivity was also limited by exotic annual grass invasion and conifer encroachment. Mesic habitat availability was a function of topographic relief, mean elevation, annual mean snow water equivalent, and winter temperatures, indicating that snowpack recharges the late summer mesic resources that support sage-grouse productivity. Management actions focused on maintaining and restoring mesic resources and drought resilient habitats, limiting the spread of exotic annual grasses, and reversing conifer encroachment should support future sage-grouse recruitment and help mitigate the effects of climate change.
... Taller trees may provide avian predators with more or better perches (Andersson et al., 2009), and visibility (e.g. of approaching predators) is likely to be reduced in areas surrounding taller forests. Forest height can also be an indicator of forest age, which could impact bird density in the surrounding habitat, as any reduction in productivity, recruitment and survival will take some time to manifest, particularly for long-lived species with high breeding site fidelity, such as waders (Halldórsson et al., 2008;Méndez et al., 2018). ...
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Planting forests is a commonly suggested measure to mitigate climate change. The resulting changes in habitat structure can greatly influence the diversity and abundance of pre‐existing wildlife. Understanding these consequences is key for avoiding unintended impacts of afforestation on habitats and populations of conservation concern. Afforestation in lowland Iceland has been gaining momentum in recent years and further increases are planned. Iceland supports internationally important breeding populations of several ground‐nesting, migratory bird species that mostly breed in open habitats. If afforestation impacts the distribution and abundance of these species, the consequences may be apparent throughout their non‐breeding ranges across Europe and Africa. To quantify the effects of plantation forests on the abundance and distribution of ground‐nesting birds (in particular waders, Charadriiformes), surveys were conducted on 161 transects (surrounding 118 plantations) perpendicular to forest edges throughout Iceland. The resulting variation in density with distance from plantation was used to estimate the likely changes in bird numbers resulting from future afforestation plans, and to explore the potential effects of different planting configuration (size and number of forest patches) scenarios. Of seven wader species, densities of five (golden plover Pluvialis apricaria, whimbrel Numenius phaeopus, oystercatcher Haematopus ostralegus, dunlin Calidris alpina and black‐tailed godwit Limosa limosa) in the 200 m surrounding plantations were just under half of those further away (up to 700 m). Redshank Tringa totanus densities were lowest ≤150 m from the plantation edge while snipe Gallinago gallinago densities were 50% higher close to plantations (0–50 m) than further away (51–700 m), and no consistent effects of plantation height, diameter, density or type were identified. Plantations are typically small and widespread, and simulated scenarios indicated that total declines in bird abundance resulting from planting trees in one large block (1,000 ha) could result in only ~11% of the declines predicted from planting multiple small blocks (1 ha) in similar habitats. Synthesis and application. Planting forests in open landscapes can have severe impacts on populations of ground‐nesting birds, which emphasizes the need for strategic planning of tree‐planting schemes. Given Iceland's statutory commitments to species protection and the huge contribution of Iceland to global migratory bird flyways, these are challenges that must be addressed quickly, before population‐level impacts are observed across migratory ranges.
... For most herbivorous individuals, whether to choose a habitat structure with high vegetation gaps and visibility requires a trade-off between finding food and shelter (Ewald et al., 2014). Understory gaps and visibility within the threshold range are conductive to species activity and aggregation (Schnitzer et al., 2001;Andersson et al., 2009;Aben et al., 2018). However, too large understory gaps and visibility would detrimental to species diversity of understory, the clearing of understory vegetation led to the loss of partial ecological niche, which makes some vulnerable species, such as birds, insects and small mammals, at a disadvantage in competition (Bradbury et al., 2005;Blackey et al., 2017;Vries et al., 2021). ...
Article
Three-dimensional (3D) vegetation structure is vital in maintaining the functions of forest ecosystems and species diversity. Temperate forests of Northeast Asia support a variety of fauna but is also affected by large herbivore disturbances or management practice (e.g., livestock grazing), resulting in varying degrees of habitat degradation and fragmentation in many areas. However, traditional methods lack the quantification of 3D vegetation structure at a fine scale, which makes it difficult to obtain complete and accurate detailed data on the multi-level structure below the canopy and limits our understanding of the impact of disturbance on habitat quality and species diversity. In this study, terrestrial laser scanning (TLS) data were used to quantify the 3D habitat structural characteristics of different stand types affected by forest management or large herbivore activities (deer-browsed forest, livestock-grazed forest, secondary forest, and mixed forest) in Northeast China. TLS-derived parameters in this study revealed the subtle changes of habitat structures below the canopy: 1) livestock-grazed forest had a much lower canopy height, tree number, and stem volume than that of the other stand types; 2) the vegetation area index (VAI) of low canopy height (0–5 m) in livestock-grazed forest and deer-browsed forest were significantly lower than those in secondary and mixed forest with less disturbance; 3) intensive large herbivores activities led to the larger understory gaps and visibility in livestock-grazed and deer-browsed forest. TLS-derived parameters in this study are implicated in wildlife habitat selection and fitness, which contribute to revealing fine scale habitat structure-species diversity relationships. In forest management, it is proposed to use TLS to quantify the structural and functional attributes of habitats from a new perspective, thus guiding conservation practices at local scale to balance the relationship between plants and animals.
... Additionally, juniper expansion may fragment large expanses of sagebrush (e.g., Fuhlendorf et al. 2002), possibly leading to density-dependent effects on Sage-Grouse concentrated into remaining pockets of suitable habitat. Juniper trees may also expand suitable habitat for avian predators (Andersson et al. 2009;Coates et al. 2014), potentially increasing the risk of predation for Sage-Grouse. Invasive grasses, such as cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae (L.) Nevski), can have a similar impact on Sage-Grouse habitat; an increase in invasive grass density reduces native grass and perennial forb cover (Billings 1994;Davies 2011), which could reduce the availability of cover and food required for nesting and brood-rearing (Hagen et al. 2007;Casazza et al. 2011;Lockyer et al. 2015;Smith et al. 2018). ...
Article
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Measurement of physiological responses can reveal effects of ecological conditions on an animal and correlate with demographic parameters. Ecological conditions for many animal species have deteriorated as a function of invasive plants and habitat fragmentation. Expansion of juniper (genus Juniperus L.) trees and invasion of annual grasses into sagebrush (genus Artemisia L.) ecosystems have contributed to habitat degradation for Greater Sage-Grouse (Centrocercus urophasianus (Bonaparte, 1827); hereinafter Sage-Grouse), a species of conservation concern throughout its range. We evaluated relationships between habitat use in a landscape modified by juniper expansion and annual grasses and corticosterone metabolite levels (stress responses) in feces (FCORTm) of female Sage-Grouse. We used remotely sensed data to estimate vegetation cover within the home ranges of hens and accounted for factors that influence FCORTm in other vertebrates, such as age and weather. We collected 35 fecal samples from 22 radio-collared hens during the 2017–2018 brood-rearing season (24 May–26 July) in southwestern Idaho (USA). Concentrations of corticosterone increased with home range size but decreased with reproductive effort and temperature. The importance of home range size suggests that maintaining or improving habitats that promote smaller home ranges would likely facilitate a lower stress response by hens, which should benefit Sage-Grouse survival and reproduction.
... At these low levels of tree cover, the sagebrush understory is predominantly intact , suggesting mechanisms unrelated to understory vegetation drive changes in sage-grouse space use in areas with limited juniper cover. Encroaching juniper may provide more perch sites and increase the presence and success of sage-grouse nest predators such as the common raven (Corvus corax) and predators of adult sage-grouse such as the golden eagle (Aquila chryseatos; Wolff et al. 1999, Andersson et al. 2009). ...
Article
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Woody plant expansion into shrub and grasslands is a global and vexing ecological problem. In the Great Basin of North America, the expansion of pinyon–juniper (Pinus spp.–Juniperus spp.) woodlands is threatening the sagebrush (Artemisia spp.) biome. The Greater Sage‐grouse (Centrocercus urophasianus; sage‐grouse), a sagebrush obligate species, is widespread in the Great Basin and considered an indicator for the condition of sagebrush ecosystems. To assess the population response of sage‐grouse to landscape‐scale juniper removal, we analyzed a long‐term telemetry data set and lek counts with a Bayesian integrated population model in a before‐after‐control‐impact design. Population growth rates (λ) in a treatment area (Treatment) with juniper removal and a control area (Control) without juniper removal indicated the two areas generally experienced population increase, decrease, and stability in the same years. However, the difference in λ between study areas indicated a steady increase in the Treatment relative to the Control starting in 2013 (removals initiated in 2012), with differences of 0.13 and 0.11 in 2016 and 2017, respectively. Retrospective sensitivity analysis suggested the dynamics in λ were driven by increases in juvenile, adult, first nest, and yearling survival in the Treatment relative to the Control. These findings demonstrate the effectiveness of targeted conifer removal as a management strategy for conserving sage‐grouse populations in sagebrush steppe affected by conifer expansion. Examples of positive, population‐level responses to habitat management are exceptionally rare for terrestrial vertebrates, and this study provides promising evidence of active management that can be implemented to aid recovery of an imperiled species and biome.
... Another reason for perching is safety during roosting, caring for plumage, and feeding. Contrary to ground sitting, perches offer far better visibility (Andersson et al. 2009), making them safer against attacks by mammalian predators and much better at spotting other birds of prey that could endanger them or their broods. We confirmed that SWF and forest edges are highly important for perching birds of prey. ...
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Context Small woody features (SWF; tree lines and small woods) in agricultural landscapes provide a substitute for forest conditions for a wide range of species and a suitable edge habitat for ecotone species. The importance of SWF for biodiversity is usually inferred from presence or abundance data for small animals. Although large animals, due to their lower density are less likely to be attributed with SWF, they may depend on these areas to effectively utilize the agricultural landscape matrix. Objectives We followed movements of three avian predator species (northern goshawk, common buzzard, and lesser spotted eagle) in the breeding and post-breeding season to assess their dependence on SWF in agricultural landscapes and to determine the characteristics of woods influencing each species. Methods We compared time spent flying and perching, where perching sites were classified as open space, forest interior, forest edge, and SWF. Next, the relative importance of SWF and forest edges, as well as specific characteristics of each habitat, were evaluated using resource selection functions. Results All species spent most of the daytime perching, and preferentially utilized SWF and forest edges. Buzzards and eagles were not influenced by the characteristics of SWF, but goshawks preferred relatively large, dense patches. Conclusions We conclude that SWF are crucial for exploitation of agricultural landscapes by avian predators by providing suitable perching sites for foraging. We also detected variation in the quality of perching sites, suggesting that for some species (like the goshawk), artificial perching sites cannot compensate for a lack of SWF.
... This issue likely affects other small tortoise species: all but one dead tent tortoises (80 %) were found along mesh fences. Even if not trapped by the mesh, small tortoises may be more vulnerable to predators along fences, because fences provide lookout posts for crows and other predatory birds, increasing predation pressure (Andersson, Wallander, & Isaksson, 2009). Predation risk may be further increased by clearing of vegetation along fence lines, increasing the visibility of small tortoises. ...
Article
Fencing, including electric fencing, is widely used across South Africa for livestock and game ranching practices. Leopard tortoises (Stigmochelys pardalis) are particularly prone to being killed by electric fences, but no published studies have assessed the impact of fence structure or quantified tortoise mortality along non-electric fences. This is a conservation concern, especially because South Africa is home to more tortoise species than any other country. This study relates tortoise mortality associated with electrified and non-electrified fences to fence structure, and uses transects away from fences as a comparison to estimate the impact of fences on mortality. All fence types had significantly higher tortoise mortality than open veld transects. Leopard tortoise mortalities were greatest along electric fences (56 % of mortalities), even though these comprised only 4% of fences in the study. By comparison, most angulate tortoises (Chersina angulata) died after becoming wedged in mesh fences. The distribution and abundance of fence types along 2200 km of roads was used to extrapolate the impacts of different fence types on tortoises in the southeastern Karoo, South Africa. A survey of land-use types indicated that game farms were more likely to be associated with the presence of electric fences. Regulations are needed to limit mortality of vulnerable species (tortoises, pangolins) on electric fences by setting a minimum strand height and ‘escape’ periods implemented through randomized off times or thermostatic switches.
... A number of behavioral mechanisms may influence these patterns. For example, grasslands bordered by trees or containing tall objects may be avoided due to predator use of these objects as perches, and the resulting increase in mortality risk to prey species (van der Vliet et al. 2008, Andersson et al. 2009). Individual birds may also perceive a tall object on the horizon as indicative of less available suitable habitat within an otherwise large patch. ...
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The Saltmarsh Sparrow (Ammospiza caudacuta) is a tidal marsh bird facing rapid population decline throughout its range, largely caused by degradation and loss of breeding habitat. Thus, there is a need to preserve tidal marshes in the northeastern United States, but to do so requires an understanding of the habitat features that support robust populations. Previous studies have shown Saltmarsh Sparrow abundance increases with marsh size, but in similar bird species, area sensitivity is more directly linked to edge avoidance. Whether additional landscape features affect the abundance of Saltmarsh Sparrows is unknown. We explored how the height of objects on the horizon, an index of habitat openness, affected the abundance of Saltmarsh Sparrows. Our primary goal was to determine whether the angle to the highest point on the horizon (“angle to maximum horizon”) predicted abundance better than marsh area or distance to the marsh edge. We used N-mixture models to evaluate the combination of spatial factors that best predicted Saltmarsh Sparrow abundance while also accounting for survey-level variables that could influence detection probability. We found that the interaction between distance to edge and angle to maximum horizon best predicted abundance. Taller objects on the horizon were negatively correlated with bird abundance, and this effect was strongest within 50 m of the marsh edge. When we considered the predictive powers of patch area, distance to edge, and angle to maximum horizon individually, angle to maximum horizon was the best single predictor. We found the highest abundance of Saltmarsh Sparrows at point locations where the angle to maximum horizon was 0.0°, and at angles greater than 12° the predicted abundance fell below 1 bird per survey point. We propose that managers should prioritize marsh openness and experimentally test the effect of marsh edge manipulations when making conservation decisions for this rapidly declining species.
... Likewise, shape of a burn unit can affect a species' ability to traverse and occupy patches because of the relationship between perimeter-area ratios and core areas (Helzer and Jelinski 1999). For species like turkeys, burn units with increased perimeter-area ratios provide a greater number of unburned areas juxtaposed to burned areas if the area of burned units is similar, thereby reducing movements necessary to reach escape cover during or after fires (Andersson et al. 2009, Lavoie et al. 2010) and during recolonization of burned areas immediately following fire (Yeldell et al. 2017c). Hence, altering burn unit shape to increase perimeter-area ratio may enhance the ability of turkeys to move to unburned patches juxtaposed to burned areas, increasing use of recently burned units (Lima andDill 1990, Fischhoff et al. 2007). ...
Article
In recent years, there have been increasing efforts to understand effects of prescribed fire on population dynamics of wild turkeys (Meleagris gallopavo; turkeys) in pine (Pinus spp.) forests. Although distribution of turkeys is not limited to pine forests, these forests provide nesting and brood-rearing habitat throughout the southeastern United States. Previous studies have investigated direct (e.g., nest loss to fire) and indirect (e.g., nest-and brood-site selection) effects of prescribed fire, but little is known about how turkeys are influenced by the spatial scale and shape of prescribed fire. We constructed an individual-based model (IBM) with landscapes of 2 burn unit shapes and 17 spatial scales. We used telemetry data obtained from global positioning system-marked female turkeys to replicate movement behaviors of turkeys within the model. We hypothesized that use of units burned during the current year (<1 yr) would decrease as scale of fires increased, and that shape of burn units would influence use by turkeys. Spatial scale most influenced turkey use; the greatest use was in burned stands of approximately 23 ha in size, whereas least use was associated with burned stands >1,269 ha. At a spatial scale of 23 ha, the daily percent use of rectangular burn units was 7% greater than square-shaped burn units. Likewise, daily percent use of rectangular burn units was 34% greater than square-shaped burn units at a spatial scale of 1,269 ha. When burn units were rectangular-shaped, daily percent use decreased by 48% as the spatial extent of the fires increased from 23 ha to 203 ha. Likewise, when burn units were square-shaped, turkey use decreased by 49% as spatial extent of fires increased from 23 ha to 203 ha. Our findings suggest the importance of managing forested landscapes with prescribed fires not exceeding approximately 200 ha if wild turkeys are a management concern.
... Raptors typically choose the highest perches available to them, so increasing the height of our perches could also encourage greater use (Andersson, Wallander, & Isaksson, 2009). American kestrels and great horned owls used 2.5 m perches in the absence of 5 m perches, but when perches of these heights were paired they preferentially used the taller perches (Hall et al., 1981), a pattern also observed at artificial perches on reclaimed strip mines in West Virginia (Forren, 1981). ...
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Cover crops are an increasingly common conservation practice in intensive row‐crop agriculture of the Midwestern United States and can improve wildlife habitat. However, they also benefit agricultural pest species such as voles (Microtus), which have damaged cover‐cropped soybean fields in Indiana. We tested the feasibility of attracting raptors, which are natural predators of voles, to cover‐cropped fields by supplying artificial perches from which to hunt. We assessed raptor use of artificial perches in cover‐cropped fields during the winters of 2018 and 2019. Perches were erected at three different distances from the field edge: 50, 125 and 200 m. We modelled perch use of our three most common species, great horned owl, red‐tailed hawk and American kestrel, with a logistic generalised linear mixed model. Raptors used 82% of the perches, and perch use was greatest at 200 m. However, even at peak use, our best model predicted a low probability of overall perch use for all three species. Artificial perches can attract raptors into large row‐crop fields. Sturdier perch design, extended perch availability and greater vole populations could increase use of perches. Although raptor perch use by itself is unlikely to control vole populations in cover‐cropped fields, artificial perches could form a valuable component of an integrated pest management system.
... In Alcedo and El Cura, birds foraged from low perches in an area dominated by low vegetation due to giant tortoises or cows. Several studies showed that perch height (Butler and Gillings 2004, Douglas et al. 2009, Martínez et al. 2010 and distance between bird and prey can influence prey detectability and hunting success (Getty and Pulliam 1991, Malan and Crowe 1997, Andersson et al. 2009). Also open patches with direct sun exposure are favorable to thermophilic arthropods (Liu et al. 2013), and flying insects such as moths benefit from open areas as their dispersal depends on finding new foraging grounds (Young 1977). ...
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In the Galápagos Islands many endemic bird species, including the emblematic Darwin's finches, show significant declines in population size. The endemic little vermilion flycatcher Pyrocephalus nanus , classified as vulnerable with high extinction risk, is strongly declining and broods regularly fail. We investigated multiple causes for breeding failure by comparing breeding success, infestation intensity by the hematophagous larvae of the introduced parasitic fly Philornis downsi , predation, parental food provisioning rate and prey attack rates as indicators of food availability at three study sites differing in anthropogenic habitat alterations: Alcedo on Isabela Island with its pristine habitat remote from human settlements, El Cura, also on Isabela Island but dominated by farmland, and Mina Roja on Santa Cruz Island, a site highly altered by introduced invasive plant species, mainly the blackberry. To test for the causal role of parasitism, we reduced the number of P. downsi larvae in half the nests at each site on Isabela Island, and used the other nests as control. When infestation intensity was experimentally reduced, both breeding success and food provisioning rates increased significantly in El Cura, but not in Alcedo, where breeding success and food provisioning rates were overall higher and infestation intensity lower than in El Cura. In the very small population of the little vermilion flycatcher in Mina Roja most nests were abandoned during the incubation phase before nests were infested by P . downsi . Mammalian predation played a minor role in brood loss at all three study sites. Our experimental study demonstrates that the recently introduced parasitic fly significantly affects breeding success of an endangered endemic bird species, and suggests that the effects are modulated by natural levels of P. downsi infestation and habitat‐related rates of food provisioning. Conservation measures should include P. downsi control combined with creating and maintaining open foraging areas. This article is protected by copyright. All rights reserved.
... Visual information can influence animal behaviour and fitness in diverse and important ways. Prey species that detect predators can take evasive actions (Lima & Dill, 1990), and predators that rely on vision for hunting can locate prey and evaluate costs and benefits of pursuit (Andersson, Wallander, & Isaksson, 2009). For many species, visibility of the surrounding area influences selection of sites used for nesting, mating and foraging (e.g. ...
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Visual information affects animal behaviour and fitness in diverse ways, but a lack of suitable methods to quantify visibility in three‐dimensional (3D) environments limits applications of the concept of visibility in ecological research. The viewshed3d r package is dedicated to quantifying the visual environment from a single location or from a cumulation of viewpoints based on 3D point clouds acquired with terrestrial laser scanning. We present the entire workflow required to prepare the data and perform the visibility analyses in viewshed3d. This approach can help unlock the potential contributions of viewshed analyses to the emerging subdiscipline of ‘viewshed ecology’.
... Herbaceous vegetation comprises a substantial component of turkey diets (Exum et al. 1987;Hurst 1992), and changes in groundcover vegetation (Wiggers et al. 2013), herbaceous plants (Ellair and Platt 2013), and invertebrates (New 2014) after prescribed fire may shift forage availability (Campo et al. 1989;Burk et al. 1990;Sisson et al. 1990;Still and Bauman 1990). Likewise, sparse understory immediately following prescribed fire but before plant regrowth (Lavoie et al. 2010), coupled with decreases in midstory structure, may shift available concealment and escape cover (Andersson et al. 2009). Additionally, female turkeys inhabiting landscapes in southeastern United States that are managed with prescribed fire encounter a dynamic landscape as fire events occur concurrent with reproductive efforts (Yeldell et al. 2017a;Wood et al. 2018). ...
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Background Behavioral responses are the most immediate ways animals interact with their environment, and are primary mechanisms by which individuals mitigate mortality risk while ensuring reproductive success. In disturbance-driven landscapes, animals must adjust behaviors both spatially and temporally to maximize individual fitness. Prescribed fire is an important ecosystem driver in many coniferous forests, as fire cycles nutrients, creates spatially heterogeneous distributions in quantity and quality of forage and cover, and provides opportunities for fire-adapted taxa. Because fire immediately shifts resource distribution, and fire characteristics may drive behavioral responses to recent burns, we examined behavioral responses of 105 Global Positioning System (GPS)-tagged female eastern wild turkeys ( Meleagris gallopavo silvestris Linnaeus, 1758) to fire application at three sites in southeastern United States. We used satellite-derived imagery to calculate burn severity and burn heterogeneity. We also calculated distance to adjacent unburned stands and time-since-fire at GPS locations of each turkey while inside burned stands. We used behavioral change point analyses to estimate behavioral state for turkeys using burned areas, and generalized linear mixed models to estimate how fire characteristics affected turkey behavior inside burned areas. Results Turkeys focused their use in less severely burned areas, and were less likely to use the interior of burned areas. Turkeys were more likely to forage and rest in less severely burned areas, suggesting that managers should apply prescribed fire frequently enough to promote low-severity burns. We found that, as distance to neighboring unburned areas increased, turkeys were more likely to walk through the interiors of recently burned areas, as opposed to resting or foraging in them, suggesting that the interiors of some burn units are less suitable habitat in the year that prescribed fire is applied. Our findings suggest that prescribed fire applied to ensure that interior areas of burned stands are <250 m from adjacent unburned stands or to stands shaped to maximize edge-to-area ratios likely create more suitable conditions for foraging and resting. Conclusions The application and spatial arrangement of prescribed fire, even in frequently burned areas, affect animal response and behaviors. Prescribed fire regimes should be created in recognition that sizes of burned stands and fire severity, along with determinants of fire severity ( e.g., fuel loads, return intervals, timing), are important influences on animal behavior in frequent-fire-managed landscapes.
... Foraging on a substrate is also associated with increased responsiveness to alarm calls compared to aerial foraging, presumably because aerial foragers are better able to detect predators (Mart ınez & Zenil 2012). In addition, many predators prefer to search for and attack prey from above (G€ otmark & Post 1996;Andersson et al. 2009). By distinguishing ground foraging from foraging at different vegetation heights we are also likely to capture niche-scale differences in habitat cover (G€ otmark & Post 1996;Sorato et al. 2012). ...
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Some birds undergo seasonal colour change by moulting twice each year, typically alternating between a cryptic, non‐breeding plumage and a conspicuous, breeding plumage (‘seasonal plumage colours’). We test for potential drivers of the evolution of seasonal plumage colours in all passerines (N = 5901 species, c. 60% of all birds). Seasonal plumage colours are uncommon, having appeared on multiple occasions but more frequently lost during evolution. The trait is more common in small, ground‐foraging species with polygynous mating systems, no paternal care and strong sexual dichromatism, suggesting it evolved under strong sexual selection and high predation risk. Seasonal plumage colours are also more common in species predicted to have seasonal breeding schedules, such as migratory birds and those living in seasonal climates. We propose that seasonal plumage colours have evolved to resolve a trade‐off between the effects of natural and sexual selection on colouration, especially in seasonal environments.
... Females also selected ground roosts in areas with higher ground cover and lower vegetation. Higher ground cover and lower visual obstruction, coupled with increases in midstory structure in stands !2 years post-fire, may aid in predator detection and decrease search efficiency of avian (Andersson et al. 2009) and mesomammal (e.g., bobcat [Lynx rufus], Kolowski and Woolf 2002;raccoons, Bowman and Harris 1980) predators. Thus, these stands provide important vegetation communities where brooding females can safely detect and avoid predators while ground roosting (Tisdale andFernandez-Juricic 2009, Javůrkov a et al. 2012). ...
Article
Management of longleaf pine (Pinus palustris) forests relies on frequent prescribed fire to maintain desirable plant communities. Prescribed fire is often applied while female wild turkeys (Meleagris gallopavo) are reproductively active and may immediately affect habitat availability and demographic outcomes. We identified covariates affecting selection of areas used by nesting and brooding females and determined if these covariates influenced nest and brood survival in a longleaf pine ecosystem. We captured 63 female wild turkeys and measured vegetation and landscape characteristics surrounding nests, brood roosts, and daytime use sites. We used conditional logistic regression to determine which vegetation and landscape‐scale characteristics influenced nest, brood roost, or daytime use sites. We generated Cox proportional hazard models at multiple spatial scales to determine if selection influenced nest and brood survival. Females selected nest sites with greater visual obstruction and increased ground cover, and also nested closer to roads. We observed relevant differences in vegetation and landscape variables associated with where females chose to roost broods compared to sites chosen for foraging or loafing. Females roosted broods at sites with increased ground cover and decreased visual obstruction, and daytime use by broods was most related to increases in ground cover. Time‐since‐fire was an informative covariate for brood site selection but not for nest site selection. Females selected brood roost sites in stands not recently burned (3–6 yr post‐fire), and selected daytime use sites in stands burned the current year (0 yr post‐fire) and 2 years post‐fire. We failed to observe links between selection of vegetation and landscape covariates and probability of nest or brood survival. Notably, our results suggest short (i.e., 1–2 yr) fire return intervals do not provide vegetation communities selected by females to roost broods. Conversely, stands burned within the current year were important for daytime use by broods. Collectively, our findings demonstrate the importance of maintaining diverse fire return intervals to ensure availability of vegetation conditions necessary for nesting and brooding. © 2018 The Wildlife Society. Our findings generally support other recent works suggesting that a 3‐year fire return interval provides vegetation communities important throughout the reproductive phases of wild turkeys. We found, however, that the intensive fire regimes used on our study site are not uniformly ideal for producing conditions needed by brooding females; these short (i.e., 1–2 yr) fire return intervals were not selected by females to roost broods.
... The presence of perches can facilitate and increase hunting efficiency due to improved visibility and reduced energy expenditure associated with hovering (see Andersson, Wallander, & Isaksson, 2009;Fig. 2). ...
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Novel ecosystems (‘emerging ecosystems’) result when species occur in combinations and relative abundances that have not occurred previously within a given biome, due to deliberate or inadvertent human agency. Humans have changed the environment through disturbance, physical structures or additional resources. Many vertebrate predators inhabit cities, towns and other places that humans have built or altered, and make use of these anthropogenic niches. These predators range in size from bats swarming around lamp posts, to leopards stalking domestic animals in the heart of cities. In this essay, we describe four scenarios where predators opportunistically make use of anthropogenic niches. First, humans are surrounded by animals, including synanthropic rodents and birds, livestock and pets, that can be novel prey for opportunistic predators. Second, feeding on prey concentrations created through anthropogenic niches increases their hunting efficiency, by reducing both search and commute times. Third, anthropogenic environments create novel situations such as thermals and artificial lighting that advantage some predators, increasing their capture success. Finally, many predators have developed novel hunting strategies to make the most of opportunities in anthropogenic environments that can lead to greater hunting success. We give examples of these four scenarios and have developed a conceptual model that captures the common mechanisms relevant to each, with predictions for how these can be explored further in future studies. Predators exploiting anthropogenic niches can experience greater ease of hunting, decreased search effort and/or increased capture success. Consequently, these animals experience many physiological and reproductive benefits over conspecifics that do not make similar use of anthropogenic niches, ultimately benefitting from living alongside humans.
... Complex vegetation structure has been shown to increase the abundance and diversity of generalist predators with attendant consequences for prey , LaManna et al. 2015. For example, Andersson et al. (2009) found that predator hunting efficiency increased with perch availability and perch height in open landscapes. Compared with hovering, predators hunting from perches minimize their energy cost, and are able to increase their prey detection and capture efficiency (Kramer and McLaughlin 2001, Leyhe and Ritchison 2004, Tomee et al. 2011. ...
... Similar studies have shown that in other grassland birds, habitat patches with low horizons that lack elevated structures are preferred to those with tall objects (e.g., trees, telephone poles, wind turbines; e.g., Bakker et al. 2002, Ribic et al. 2009, Thompson et al. 2014), but the extent to which these results can be expanded to marsh systems is less well-known. Marshes bordered by trees or containing tall objects may be avoided due to the probability of predators using these objects as perches from which to spot prey (van der Vliet et al. 2008, Andersson et al. 2009). Additionally, individual birds may perceive marsh area differently from how humans delineate marsh patches from aerial imagery. ...
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The Saltmarsh Sparrow (Ammodramus caudacutus) is a tidal marsh bird species facing rapid population decline throughout its range. A major cause of this decline is degradation and loss of breeding habitat, and thus there is a need to preserve coastal marshes in the northeastern United States. To do so requires an understanding of the habitat features that support robust populations. Previous studies have shown increases in Saltmarsh Sparrow abundance with marsh size increases. In other grassland bird species, habitat patches with low horizons are preferred to those with tall objects (e.g., trees, telephone poles, wind turbines). This study tests how the abundance of Saltmarsh Sparrows is affected by the maximum height of objects in the horizon of marshes. Abundance data were collected via point count surveys at 1,698 points from Maine to Virginia during the 2012 breeding season. At each of these points, a clinometer was used to determine the height of objects in the horizon. Using program R, we evaluated detection and site covariates to determine the model which best predicted the abundance of Saltmarsh Sparrows. Our study found that the angle to the maximum horizon, which considers a bird’s perception of its surroundings, is a better predictor of abundance than marsh patch size. We found that the highest abundance of this species was observed in marshes where the angle to the horizon was zero degrees, and at angles greater than 13 degrees the predicted abundance fell below one bird per point. This implies that perceived openness, rather than a large area, is selected by this species, and should be a prioritized marsh characteristic for the conservation of Saltmarsh Sparrows.
... falcons) prefer high perches, which give them the greatest visibility, whereas predators that use auditory cues (e.g. owls) prefer lower perches (Kay et al. 1994;Andersson et al. 2009). The exact height preference of perches appears to be species-specific (e.g. in lucerne (Medicago sativa) crops in the United States, American kestrels and great-horned owls (Bubo virginianus) preferred to hunt using taller 5-m high perches instead of 2.5-m high perches, while barn owls (Tyto alba) used perches of any height (Hall et al. 1981)). ...
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Context Birds active in vineyards in south-eastern Australia can reduce or enhance crop yields via their foraging activities (e.g. by consuming grapes or by preying on grape-eating species). Aims We examined the effectiveness of artificial perches in encouraging predatory birds into vineyards to scare frugivorous birds and consequently reduce the damage they cause to grapes. Methods We monitored 12 artificial perches for 4 months during the growing season, spread over six vineyards in north-eastern Victoria, and compared bird damage to grapes at these sites with control sites without perches. Key results We found that raptors did not use the artificial perches. However, the large and aggressive Australian magpie (Cracticus tibicen) commonly used perches and we recorded 38 513 perch visits by this species. Grapevines around perch sites suffered >50% less grape damage (4.13% damage per bunch) than control sites (8.57% damage per bunch). Conclusions Our results suggest that providing artificial perches in vineyards can play a role in reducing frugivore damage to grapes. However, the effectiveness of perches can vary under different environmental conditions and certain perch types are not suitable for all predatory or aggressive birds. Implications Future research should focus on the potential role of large-bodied and competitively aggressive species such as the Australian magpie in altering the activity of smaller frugivorous birds in vineyards, and also on the optimum height and location of artificial perches within vineyards to increase visitation by other predatory or aggressive bird species.
... Complex vegetation structure has been shown to increase the abundance and diversity of generalist predators with attendant consequences for prey (Gorini et al., 2012;LaManna et al., 2015;Oliver et al., 2009). For example, Andersson, Wallander, and Isaksson (2009) found that predator hunting efficiency increased with perch availability and perch height in open landscapes. Compared to hovering, predators hunting from perches minimize their energy cost and are able to increase their prey detection and capture efficiency (Leyhe & Ritchison, 2004;Tomee, Dias, Chumbinho, & Bloise, 2011). ...
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The likelihood of encountering a predator influences prey behavior and spatial distribution such that non-consumptive effects can outweigh the influence of direct preda-tion. Prey species are thought to filter information on perceived predator encounter rates in physical landscapes into a landscape of fear defined by spatially explicit het-erogeneity in predation risk. The presence of multiple predators using different hunting strategies further complicates navigation through a landscape of fear and potentially exposes prey to greater risk of predation. The juxtaposition of land cover types likely influences overlap in occurrence of different predators, suggesting that attributes of a landscape of fear result from complexity in the physical landscape. Woody encroachment in grasslands furnishes an example of increasing complexity with the potential to influence predator distributions. We examined the role of vegetation structure on the distribution of two avian predators, Red-tailed Hawk (Buteo jamaicensis) and Northern Harrier (Circus cyaneus), and the vulnerability of a frequent prey species of those predators, Northern Bobwhite (Colinus virginianus). We mapped occurrences of the raptors and kill locations of Northern Bobwhite to examine spatial vulnerability patterns in relation to landscape complexity. We use an offset model to examine spatially explicit habitat use patterns of these predators in the Southern Great Plains of the United States, and monitored vulnerability patterns of their prey species based on kill locations collected during radio telemetry monitoring. Both predator density and predation-specific mortality of Northern Bobwhite increased with vegetation complexity generated by fine-scale interspersion of grassland and woodland. Predation pressure was lower in more homogeneous landscapes where overlap of the two predators was less frequent. Predator overlap created areas of high risk for Northern Bobwhite amounting to 32% of the land area where landscape complexity was high and 7% where complexity was lower. Our study emphasizes the need to evaluate the role of landscape structure on predation dynamics and reveals another threat from woody encroachment in grasslands. K E Y W O R D S avian predators, habitat complexity, landscape of fear, Northern Bobwhite, predation risk, vegetation structure
... Likewise, increases in ground cover vegetation (Wiggers et al., 2013), herbaceous plants (Ellair and Platt, 2013), and invertebrates (New, 2014) may increase concealment and forage availability (Campo et al., 1989;Burk et al., 1990;Sisson et al., 1990;Still and Bauman, 1990). However, the sparse understory immediately after prescribed fire but before plant regrowth (Lavoie et al., 2010), coupled with decreases in midstory structure may increase search efficiency of avian predators (Andersson et al., 2009), and remove possible escape cover. These changes in forage availability and predation risk suggest habitat quality may differ within a burned stand. ...
Article
Prescribed fire is used in southeastern pine forests to maintain desirable forest conditions and provides herbaceous understory plant communities for wildlife. However, it is unclear how time-since-fire affects the short-term response of wild turkeys (Meleagris gallopavo) to prescribed fire. We examined use of recently burned pine stands by female eastern wild turkeys (M. g. silvestris) immediately following prescribed fire in a pine-dominated landscape managed with frequent fire. We developed several models to best predict the influence of time-since-fire and month of fire application on turkey use of burned areas. We also assessed the spatial behavior of turkeys when using recent burns to determine if distance to escape cover affected turkey use of recently burned areas. Female turkeys used burned areas immediately after fire and probability of use increased until 141 days post-fire and then declined until 250 days post-fire when data collection stopped. Response of turkeys to recent burns depended on the month of prescribed fire application; probability of use was greater for areas burned in February and during the growing season (April and May). Turkey use of space within burned areas declined as distance to surrounding unburned areas increased, suggesting that turkeys favor the edge of burned and unburned areas which could serve as escape cover. However, the effect of distance to the perimeter of burned stand decreased as time-since-fire increased. Our findings suggest that turkeys are less likely to use areas burned in early winter (e.g., December) than late winter (e.g., February), and are more likely to use space near edges of burned areas than the interior. We recommend managers in southeastern pine-dominated ecosystems apply dormant season fires in late winter and apply early spring growing season fires as needed to meet forest management objectives. Turkeys used burned areas immediately following prescribed fire, but traded-off exploitation of foraging opportunities by using space near escape cover. Applying prescribed fire on smaller patches in checkerboard fashion may enhance turkey use of the entirety of a burn unit, and future research should seek to delineate other variables influencing how turkeys use recently burned areas. We recommend applying prescribed fire to patches smaller than those burned on our study sites at frequent (2–3) year fire-return intervals to increase usable space for female turkeys throughout the reproductive period.
... For instance, patch characteristics are important for Burrowing Owls in terms of predator detection and access to food resources. The presence of perches near the nest provide improved vigilance behavior, since elevated positions increase an owl's field of vision and may help it to detect predators earlier (Widén 1994, Andersson et al. 2009, Scobie et al. 2014). In addition, perches may be used during foraging, especially for searching prey through sit-and-wait hunting mode (Bellocq 1987). ...
Article
Habitat modifications have led many bird species to occupy areas with different characteristics, including human-altered landscapes. In this study, we analyzed how land use influences the nest-site selection at the microscale level by Burrowing Owls (Athene cunicularia) breeding in vegetated sand dunes, periurban areas, and agroecosystems in the Pampas of Argentina. We compared the characteristics of the nest site (percentage of open space) and the nest patch (distance to conspecific nests, tall vegetation and perches and number of perches) within and among the three land-cover types. In addition, we evaluated the breeding performance (nesting success and productivity) of owls nesting in these land-cover types. We found that nest microsite variables did not vary between owl-occupied and owl-unoccupied sites within nest patches, but they differed among land-cover types. Although nest patches differed in their availability of perches at each land-cover type, distance from the nest to the nearest perch did not vary between them. Distances to tall vegetation and to conspecific nests were highly variable and did not differ among land-cover types. Our results indicate that Burrowing Owls that inhabit the Pampas used a variety of land-cover types for nesting and showed little selectivity of nest sites and nest patches, thus reinforcing the idea that they are habitat generalists.
... Studies on the perceptual distance for these three species were hard to find. However, for smaller and simpler predator-prey systems such as backswimmers (Gergs and Ratte, 2009;Gergs et al., 2010) and raptors (Andersson et al., 2009), empirical data from laboratory and field experiments are available. Recent studies showed that animal body masses might play a role in the utilisation of space (Jetz et al., 2004) and that encounter distances can be expressed as a function of insect larval stage (Gergs and Ratte, 2009). ...
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Shrublands globally have undergone structural changes due to plant invasions, including the expansion of native trees. Removal of native conifer trees, especially juniper (Juniperus spp.), is occurring across the Great Basin of the western U.S. to support declining sagebrush (Artemisia spp.) habitats and associated wildlife species, such as greater sage-grouse (Centrocercus urophasianus). One justification for conifer removal is that it may improve survival of sagebrush-associated wildlife by reducing the abundance of avian predators. However, the relationship between conifer expansion and predator distributions has not been explicitly evaluated. Further, although structural characteristics of habitat are important for generalist predators, overall prey abundance may also affect habitat use by predators. We examined habitat use of common ravens (Corvus corax) and red-tailed hawks (Buteo jamaicensis), two generalist predators whose populations are increasing in western North America, to variation in structural characteristics and prey distributions in sagebrush habitat that has experienced conifer expansion. Structural characteristics of habitat were important predictors of habitat use for both ravens and red-tailed hawks, whereas measures of prey abundance were unimportant for both species likely because generalist predators can use a wide variety of food resources. Ravens, but not red-tailed hawks, responded positively to increasing cover of juniper and the probability of habitat use was highest (> 0.95) where juniper cover within 100 m was > 20%. Habitat use by red-tailed hawks, but not ravens, was greater near cliffs but was not associated with juniper cover. Our study suggests that the removal of conifer in similar environments may lower the probability of habitat use for ravens, a common predator with significant impacts on many prey species. Therefore, we suggest conifer removal may improve sage-grouse reproductive success and survival depending on responses to conifer removal from other predators. Our results may be reflective of similar changes in rangeland ecosystems around the world undergoing expansion of conifer and other woody vegetation. Though species identities differ from sagebrush habitats, generalist avian predators in other habitats may have similar relationships with structural resources.
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Decomposition, vegetation regeneration, and biological control are essential ecosystem functions, and animals are involved in the underlying processes, such as dung removal, seed removal, herbivory, and predation. Despite evidence for declines of animal diversity and abundance due to climate change and land-use intensification, we poorly understand how animal-mediated processes respond to these global change drivers. We experimentally measured rates of four ecosystem processes in 134 grassland and 149 forest plots in Germany and tested their response to climatic conditions and land-use intensity, that is, grazing, mowing, and fertilization in grasslands and the proportion of harvested wood, non-natural trees, and deadwood origin in forests. For both climate and land use, we distinguished between short-term effects during the survey period and medium-term effects during the preceding years. Forests had significantly higher process rates than grasslands. In grasslands, the climatic effects on the process rates were similar or stronger than land-use effects, except for predation; land-use intensity negatively affected several process rates. In forests, the land-use effects were more pronounced than the climatic effects on all processes except for predation. The proportion of non-natural trees had the greatest impact on the process rates in forests. The proportion of harvested wood had negative effects, whereas the proportion of anthropogenic deadwood had positive effects on some processes. The effects of climatic conditions and land-use intensity on process rates mirror climatic and habitat effects on animal abundance, activity, and resource quality. Our study demonstrates that land-use changes and interventions affecting climatic conditions will have substantial impacts on animal-mediated ecosystem processes.
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Beach-nesting shorebirds are declining due, in part, to human disturbance in nesting areas. Sign-posts are installed around nesting areas to protect nests from people, but they may serve as perches and attract avian predators. From March–August 2018, we used passive infrared game cameras to monitor perching activity on 15 variations of sign-post designs on 2 barrier islands in North Carolina. We observed 110 independent perching events dominated (70%) by common (Quiscalus quiscula) and boat-tailed grackles (Quiscalus major) and laughing gulls (25%; Leucophaeus atricilla). We compared how the number of days perching occurred was associated with sign shape, material, sign-construction (sign x shape), position on post, and presence/absence of a nail on top of the post. Position of the sign on the post had the strongest effect on the number of days perching events occurred (χ² = 18.62 df = 2 P < 0.001). Signs positioned flush with the top of the post were most frequently perched on (10% of perching days), followed by signs positioned lower (5%) and higher (2%) than the post top. The frequency of avian predators perching on triangular signs (8%) and rectangular signs (5%) did not differ (X2 = 2.89 df = 1 P = 0.11). While sign material (metal: 12%; laminated cardboard: 11%; plastic: 13%) did not affect the probability of perching (χ² = 1.06 df = 2 P = 0.58), triangular plastic signs (11%) had more (χ² = 6.011 df = 2 P = 0.05) perching activity than rectangle-metal (6%) and rectangle-laminated signs (6%). Presence (3%) or absence (4%) of a nail on top of posts did not affect the number of days perching occurred on a sign-post (χ² = 0.59 df = 1 P = 0.52). We recommend managers position signs high on the post to reduce occurrences of predatory perching. If a choice of sign shape and material is available, rectangular metal or laminated cardboard signs may also reduce perching activity.
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Prescribed fire is widely used in southeastern pine (Pinus spp.) forests to maintain desirable forest conditions and provide early successional vegetation. However, it is unclear how fires applied just prior to and during the reproductive cycle of ground nesting Galliformes influence resource selection. We examined the short-term influence of prescribed fire on habitat selection of female eastern wild turkeys (Meleagris gallopavo silvestris) throughout their reproductive cycle (Feb−Aug) at Kisatchie National Forest in west-central Louisiana, USA during 2014 and 2015. Kisatchie was dominated (>60%) by pine stands managed with prescribed fire at a frequent (i.e., 1–3 yr) return interval. We captured 46 females and equipped them with backpack-style global positioning system (GPS) transmitters programmed to collect relocation data hourly from 0600 to 2000 each day. We used distance-based analysis to estimate selection or avoidance of vegetation communities relative to reproductive phenology of individual females. Hardwood and mixed-pine hardwood vegetation communities were selected for before and after reproductive efforts; hardwood stands were avoided during brooding. While laying their first clutch of the reproductive period, females selected mature pines burned 0–5 months prior. Females avoided mature pine stands 2 growing seasons post-burn prior to initiating their first nests. Females avoided mature pine stands 3 growing seasons post-burn when brooding. Turkeys did not select for pine stands that had experienced ≥3 growing seasons post-burn during any reproductive period, and may avoid these stands during pre-nesting and brooding. Frequent fire return intervals maintain vegetation communities that females select at some point during the reproductive season in pine-dominated landscapes.
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The strategies by which foraging predators decide when to redirect their gaze influence both prey detection rates and the prey's ability to detect and avoid predators. We applied statistical analyses that have been used to study neural decision-making for gaze redirection in primates to 3 species of predatory birds with different sizes, visual systems, habitats, and hunting behaviors: the Northern Goshawk (Accipiter gentilis), Cooper's Hawk (A. cooperii), and Red-tailed Hawk (Buteo jamaicensis). The timing of head saccades was measured during visual searches using field video recordings of foraging raptors, and during a variety of behaviors using a miniature camera mounted on the head of a Northern Goshawk. The resulting statistical distribution of latencies (time between successive head saccades) was compared to predictions from various models proposed to describe visual search strategies. Our results did not support models that assume a constant probability of gaze redirection per unit time, a constant time for "giving up" on the visual search, or an initial setup time before visual search initiation. Instead, our data were fit best by a log-normal distribution, consistent with the raptors stochastically changing their gaze direction on the basis of accumulated environmental information. Specifically, this suggests that saccade initiation arises from a neural computation based on detection of a threshold level of a dynamically updated decision signal that encodes noisy sensory data, similar to the processes inferred from previous studies of visual search strategies in primates. The only significant between-species difference we found was a slower mean gaze-redirection rate for 2 larger species compared to the Cooper's Hawk, even though the latter has hunting behavior and maneuverability similar to that of the Northern Goshawk. Head-saccade latencies measured for a Northern Goshawk during different behaviors showed that the bird changed gaze direction significantly less frequently, on average, while perched than while in motion.
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Anthropogenic development may influence the choices animals make and their resulting reproductive success and survival. If such choices are maladaptive, the impact of changes to their habitat could be catastrophic to populations that are small or declining. The Canadian prairies have changed dramatically since European settlement. Over two thirds have been converted to cropland and the number of petroleum wells within the Burrowing Owl range has tripled over the last thirty years. It is assumed that the decline of the Burrowing Owl is linked to these changes to the prairie landscape, but so far no clear, direct links have been identified. I examined habitat selection of Burrowing Owls at several temporal and spatial scales and evaluated how habitat selection influenced survival and reproductive success. First, I identified landscape features that Burrowing Owls prefer to have surrounding their nests, and examined how these preferred features related to nest survival, fledging rate, and adult survival. Using arrival date as a measure of preference, I found Burrowing Owls prefer home ranges with more annual crop and more road surfaces. These anthropogenic landscape features had a positive influence on fledging rate, suggesting that these landscape features have not created an ecological trap for Burrowing Owls on the Canadian prairies at the home range scale. Second, I tracked adult male Burrowing Owls with GPS dataloggers and examined owl space-use during the day and night. During the day, Burrowing Owls spent more time near fences and posts, likely because they are good vantage points for detection of predators. They also avoided roads with high traffic speeds, possibly because auditory disturbance from passing vehicles interferes with their ability to communicate the presence of predators to their mates and young. At night, the infrastructure (towns, roads, petroleum facilities, and oil wells) that results from human development influenced where owls spent time much more than did sensory disturbances (artificial sound and light) emanating from these sources. However, owl selection of landscape features at night did not predict reproductive success. Instead, I found owls that spent more time near the nest burrow between sunset and sunrise had the greatest nest survival and fledging rates. The choices this endangered owl makes when hunting at night and when picking a landscape in which to settle do not seem to be maladaptive or fully explain their population decline in Canada. To better understand the Burrowing Owl decline, future studies need to focus on life history stages not examined here (e.g. post-fledging for juveniles), as well as stages that occur outside of their breeding range. My findings indicate that the Burrowing Owl has flexible habitat requirements and is able to breed successfully in a developed landscape. Such determinations will be important to make for a variety of other species to identify those that may be less likely to be able to adapt to changing landscapes.
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We investigated the impact of perch height and abundance, and the cover for prey, on the hunting tactics of perch-hunting pale chanting goshawks (Melierax canorus). Although pale chanting goshawks demonstrate a clear preference for perching on the highest available perches, the availability of perches is of more importance than height because these birds hunt almost exclusively from perches, move regularly between them, and an increased number of perches increases the area of habitat accessible for effective hunting. In Succulent Karoo, pale chanting goshawks occupied areas where perch density (16 natural and 122 artificial/25 ha) was significantly higher than in unoccupied areas (8 natural and 12 artificial/25 ha). The high proportion of cover formed by natural perches (trees and shrubs; 36%) and the low proportion of open ground (42%) resulted in Closed Spekboomveld being unsuitable for pale chanting goshawks, relative to the adjacent Open Spekboomveld that supported goshawks by offering a less restricted view of the ground and prey (perch cover 18% and open ground 49%). In Karroid Broken Veld, the combination of perch availability (3 026/25 ha) and open ground (62%) may provide the most suitable conditions for hunting rodent prey near cover or in the open. We suggest that such habitat may also provide a pathway, through fitness benefits gained, in the development of delayed dispersal and cooperative breeding in pale chanting goshawk families.
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Studies of Sparrowhawk Accipiter nisus predation have revealed a seasonal change in the predation risk of many prey species during spring and summer. Several species nesting in forest experienced decreasing risk of predation, while species in semi-open habitats (farmland, edge habitats and villages) faced increasing risk. The reason for this change could be that leafing and growth of ground vegetation during spring hamper detection and catching of prey in forest compared to villages and edge habitats, thus forcing Sparrowhawks to hunt in semi-open habitats with better visibility. We examined this possibility by measuring visibility of artificial prey in four different habitats, deciduous and coniferous forest, urban areas and edge habitats, from April to July. Although visibility decreased more in deciduous habitats than in urban or coniferous habitats from April (before leafing) to June (most vegetation developed), visibility was not lower in deciduous forest than in urban or edge habitats in the summer. However, birds observed in urban habitats were on average more exposed than birds in forest in April, and this difference increased in May. In May, urban birds were also found significantly closer to the ground than forest birds. These results suggest that prey behaviour, rather than vegetational change, determines seasonal changes in predation risk of the prey species.
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In many species of animals, foraging individuals depart from and return to a central place. In a test of a model for such central place foragers, the time spent searching at different distances from the nest was recorded in an insect-feeding bird, the Whinchat (Saxicola rubetra), with and without additional food distributed over the foraging area. The following predictions were realized: (a) the search effort per unit area decreased with increasing distance from the central place; (b) with higher initial food density, the birds searched more near the nest, and less farther away; (c) the foraging area decreased when food was added; (d) the birds took more of the available food near the nest than far from it. Further, Whinchats apparently searched for food where it was cheapest for the moment. Rapid adaptation to increased food density indicates that foraging behavior in Whinchats is under strong selection for efficiency.
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Studies of ecomorphology - the relationship among species between morphology and ecology - contain two implicit and rarely tested hypotheses: (1) that morphological differences among species result in differences in performance capability at ecologically relevant tasks, which, in turn, produce differences in behavior and ecology; and (2) that morphology, performance capability, ecology and behavior have evolved synchronously. I tested these hypotheses using the Anolis lizards of Jamaica and Puerto Rico. I measured morphological and performance variables on recently caught lizards. Movement, display rate and microhabitat measurements were made on lizards observed in the field. Body size explained most of the variation in morphology and performance ability, but was not correlated with the ecological or behavioral variables. When the effect of body size is removed from the morphological and performance variables, the ecomorphological hypotheses were confirmed. Species that were similar morphologically were also similar in performance ability, ecology, and behavior. Evolutionary changes in morphology, performance, and ecology and behavior (ecobehavior) were correlated. The morphology-ecobehavior comparison revealed that: long-legged, heavy-bodied lizards jump farther in nature, jump and display more often, walk less often, and use wide perches that are distant from the nearest available perches; and that species with many subdigital lamellae perch lower, use narrower supports, and walk more frequently. Inclusion of performance parameters revealed a relationship, in agreement with biomechanical models, between body proportions and running and jumping capability; in turn, performance capability related to locomotor patterns and microhabitat use. Despite the relationship between lamellae number and ecobehavioral variables, clinging performance did not contribute to the correlations with either morphology or ecology.
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Hunting by Aegolius funereus (L.) was studied by direct observation, and various phases of the prey capture were photographed. The owls hunted in forest land and frequented dense parts of the forest where they flew skilfully. They searched for prey from low perches, mean height 1.7 m, and waited a short time at each perch, mean 1 4/5 min. Mean distance between perches was ca. 17 m. Strikes occurred from close range, ca. 4.5 m. The owl's eyes were closed for protection just before impact. At impact the talons of both feet combined covered an area approximately 4 by 6 1/2 cm. The prey was usually killed by bites in the head or back of the neck. Due to its choice of low perches and strike from close range, the owl can make good use of auditory clues.
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We studied the influence of shoreline perch trees and human development on bald eagle (Haliaeetus leucocephalus) distribution on the northern Chesapeake Bay. Bald eagle distributions may be determined by available suitable shoreline perch areas. Models based on human development and shoreline habitat variables may alleviate problems associated with classifying bald eagle habitat by identifying characteristics predictive of eagle presence. We observed 2,962 eagles during 36 shoreline surveys and relocated 110 radio-marked eagles 1,350 times during 1985-92. We counted 5,928 suitable (height ≥6.1 m, diam at breast height [dbh] ≥20.0 cm, and shoreline accessibility ≥30°) perch trees in 229, 250- × 50-m segments along shoreline during 1990-91. Shoreline segments used by eagles had more suitable perch trees (x̄ = 30.3 vs. 22.0; P < 0.001) and a larger percentage of forest cover (x̄ = 54.9 vs. 39.4; P < 0.001) than unused segments. Suitable trees on segments with eagle use were closer to water than suitable trees on segments without eagle use (x̄ = 8.4 vs. 17.0 m; P = 0.009). Most segments classified as marsh (66.7%) were unused. Marsh segments had fewer suitable perch trees, less forest cover, and a greater mean distance from water to the nearest suitable perch tree than did other land types (P < 0.001). Developed segments had fewer suitable perch trees, less forest cover, and a shorter distance from water to the nearest suitable perch tree than undeveloped forested segments (P ≤ 0.01). Logistic regression models based on various measures of perch tree abundance and shoreline development correctly predicted eagle use for 65.9-71.0% of segments.
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We studied the nocturnal hunting behavior of eight radio- tagged Eastern Screech-owls (Otus asio; five females and three males) during the period from November 1994 through March 1995. Screech-owls selected low perches when hunting (x = 1.66 m), presumably to obtain a clear view of the ground and an unobstructed flight path to prey. Low perches may also improve the ability of screech-owls to hear and locate prey. Screech-owls used perches at different heights when hunting different types of prey and also tended to perch higher when moonlight was available, perhaps because increased light levels permit owls to rely more on vision. Only 8 of 35 attacks were successful, and this low success rate suggests that owls were more often attempting to capture small mammals rather than invertebrates. Male and female screech-owls exhibited similar hunting behavior, with no differences observed in the types of prey hunted or in giving up times. Weather conditions and season (early winter vs. late winter) had little effect on the hunting behavior of screech-owls.
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We tested the behavioral and demographic responses of American kestrels, Falco sparverius, and gray-tailed voles, Microtus canicaudus, to vegetation height and addition of perches. We conducted our experiment in sixteen 0.2-ha rodent enclosures with four replicates assigned to each of the following treatments: tall vegetation without perches, tall vegetation with perches, short vegetation without perches, and short vegetation with perches. The enclosures were stocked with 20 gray-tailed voles in early November 1998. Before perches were erected during the 12th week of the experiment, kestrels showed a preference for short-vegetation enclosures (P < 0.05). After perches were erected, kestrels used enclosures with perches, showing the greatest preference for short-vegetation enclosures with a perch. Vole populations and recruitment rates were higher in tall-vegetation enclosures than in short-vegetation enclosures, but supplemental perches did not affect vole populations or recruitment. In many agricultural areas where perches are not available, providing supplemental perches may increase accessibility to prey species that cause crop damage. Facilitating predation by raptors may reduce vole populations and reduce the need to use potentially harmful chemicals in pest population management.
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Changes in raptor and mouse abundance over time in response to the introduction of artificial perches for raptors were analysed using generalised linear models. The placement of artificial perches around the perimeter of irrigated soybean crops significantly increased the number of diurnal raptors visiting and hunting over these crops compared with untreated crops. This increased hunting pressure reduced (a) the rate at which the mouse population increased in the crops and (b) the maximum mouse population density. These effects were greater when artificial perches were placed at 100-m spacings rather than 200-m spacings. No significant reductions in mouse damage were detected as mice failed to reach threshold densities for crop damage on the untreated plots. Despite this, the use of artificial perches to attract birds of prey may be a useful addition to rodent management strategies.
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Predation is a fundamental ecological process, but there are few studies of predation risk for adult, breeding birds. In this study, we quantified Relative Predation Risk (RPR) for 46 species of passerine birds preyed on by sparrowhawks during the breeding season in south-western Sweden. The sparrowhawk is a major predator of smaller birds in Eurasian forests and woodland. Near nesting hawk pairs, prey abundance was estimated by line transects. From prey remains at hawk nests, we estimated the frequency of prey species in the diet of hawks. For each hawk pair, RPR values for different prey species were calculated. The mean RPR for each prey species, based on hawk pairs as sample units, indicated degree of overrepresentation (positive RPR) or underrepresentation (negative RPR) of the prey in the diet. Prey species with a high positive RPR nested mainly near human habitations (villages or towns), at forest edges and in farmland. However, there were marked seasonal changes in RPR. Forest birds, such as the goldcrest and wren, had the highest RPR in April. Later, the hawks seemed to hunt mainly in the habitats mentioned above, where prey were more abundant or easier to catch, resulting in increasing RPR for the house sparrow, yellowhammer, greenfinch and other species. RPR values were analysed in relation to prey body size (mass) and relative density, as well as prey foraging height and nest height (categorized from the literature). In addition, the mean perch height and mean exposure of prey species were quantified in the field. Most predation was due to the smaller male hawks, providing food for their mates and young. RPR increased with prey body size up to a mass of about 40 g, then declined with increasing body size (larger prey being more difficult to catch). RPR decreased with increasing relative density of prey species. Nest height was not correlated with RPR, but foraging height seems to be an important factor: RPR decreased with increasing foraging height. A similar result was found for mean perch height, when larger prey (over 40 g) and singing individuals were excluded from the field data. RPR increased with mean exposure of prey species when larger prey and singing birds were excluded; a combination of perch height and exposure improved the correlation with RPR. Singing birds were generally perched high in the vegetation and may not suffer high predation risk, contrary to common belief. The results of this study are discussed in relation to temporal and geographical variation in RPR and antipredator adaptations in passerine birds.
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For sit-and-wait predators like Red-tailed Hawks (Buteojamaicensis), perch sites are important components of hunting ranges. From October 1999-July 2000, perches (N = 270) used by Red-tailed Hawks in central Kentucky were located and characterized. Perches used by Red-tailed Hawks were relatively high (x = 12.3 m) in trees or on poles. Such perches provide a large, relatively unobstructed field of view and likely increase the chances of detecting prey. Red-tailed Hawks spent more time on perches before attacking than before giving up, perhaps waiting to attack prey after locating it to increase the chance of a successful attack. Characteristics of vegetation around perches used by hunting Red- tailed Hawks differed from those of areas around available (but apparently unused) sites during both the breeding and nonbreeding seasons. During the breeding season, areas used by Red-tailed Hawks had less forb cover, lower vegetation density, and shorter vegetation than available areas. During the nonbreeding season, areas used by Red-tailed Hawks were characterized by less bare ground, more grass cover, less shrub cover, fewer small trees, decreased vegetation density, and shorter vegetation than available areas. In general, used areas provided less cover, which may increase prey vulnerability.
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We studied the nocturnal hunting and diurnal roosting behavior of 17 radio-equipped Tengmalm's owls (Aegolius funereus), 12 males and 5 females, in coniferous forest during their nesting season. The owls perched lower when hunting than when roosting, probably because hunting perches were selected to minimize the predator-prey distance or to obtain unobstructed access to the ground-dwelling small mammal prey, whereas roosting perches were selected to minimize the probability of being detected by an avian predator. There was no difference between perching heights associated with giving up and prey attack, nor were there any differences between perching heights, perching times, and attack distances associated with successful and unsuccessful attacks. There were no sexual differences in perching height during hunting or roosting. However, giving-up times tended to be longer for females than for their mates, which is expected because females are larger than males, and the relative cost of flight increases with body mass. The instantaneous attack rate was independent of perching time. The owls gave up their perches at a constant rate and independently of the amount of time already spent on the perch in an exponentially decaying pattern. The owls perched longer, however, before launching an attack than before giving up, probably in order to observe detected prey until the right moment for an attack. Attack distance was independent of both perching height and perching time. Perching time was inversely related to perching height, which fits the theoretical expectation that the search area will decrease with increasing height in birds that locate prey auditorily.
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Hawk Owls (Surnia ulula) are diurnal raptors found across the northern hemisphere in open boreal forest habitats. In Fennoscandia (Finland, Sweden and Norway), their diet consists mainly of microfine rodents. The population densities of these microtines usually peak every 3-4 yr and fluctuations are geographically asynchronous. Hawk Owls respond by concentrating and breeding where and when microtine abundance is high. The resulting strong temporal and spatial short-term variation in Hawk Owl density in Fennoscandia makes any long-term population trends difficult to detect. Hawk Owls locate their prey visually from elevated perches and need ample space for long-range scanning and attack. Therefore, harvesting old forest by clear-cutting is believed to benefit the Hawk Owl. However, this may depend on the values of several variables, such as clear-cut size and shape, height of trees in clear-cut edges, density and height of residual trees left in clear-cuts after logging, type and extent of ground cover and prey species composition and abundance in clear-cuts compared to old forest. Based on data on the Hawk Owl's attack range, recommendations are made for spacing of residual trees as hunting perches. No single habitat in Fennoscandian forests seems to be superior for foraging Hawk Owls throughout the year and the effects of modern forestry on Hawk Owls, although probably positive, at present are difficult to predict.
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Foraging is one of the most important endeavors undertaken by animals, and it has been studied intensively from both mechanistic-empirical and optimal foraging perspectives. Planktivorous fish make excellent study organisms for foraging studies because they feed frequently and in a relatively simple environment. Most optimal foraging studies of planktivorous fish have focused, either on diet choice or habitat selection and have assumed that these animals used a cruise search foraging strategy. We have recently recognized that white crappie do not use a cruise search strategy (swimming continuously and searching constantly) while foraging on zooplankton but move in a stop and go pattern, searching only while paused. We have termed thissaltatory search. Many other animals move in a stop and go pattern while foraging, but none have been shown to search only while paused. Not only do white crappie search in a saltatory manner but the components of the search cycle change when feeding on prey of different size. When feeding on large prey these fish move further and faster after an unsuccessful search than when feeding on small prey. The fish also pause for a shorter period to search when feeding on large prey. To evaluate the efficiency of these alterations in the search cycle, a net energy gain simulation model was developed. The model computes the likelihood of locating 1 or 2 different size classes of zooplankton prey as a function of the volume of water scanned. The volume of new water searched is dependent upon the dimensions of the search volume and the length of the run. Energy costs for each component of the search cycle, and energy gained from the different sized prey, were assessed. The model predicts that short runs produce maximum net energy gains when crappie feed on small prey but predicts net energy gains will be maximized with longer runs when crappie feed on large prey or a mixed assemblage of large and small prey. There is an optimal run length due to high energy costs of unsuccessful search when runs are short and reveal little new water, and high energy costs of long runs when runs are lengthy. The model predicts that if the greater search times observed when crappie feed on small prey are assessed when they feed on a mixed diet of small and large prey, net energy gained is less than if small prey are deleted from the diet. We believe the model has considerable generality. Many animals are observed to move in a saltatory manner while foraging and some are thought to search only while stationary. Some birds and lizards are, known to modify the search cycle in a manner similar to white crappie.
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Redshanks Tringa totanus that are preyed upon by Sparrowhawks Accipiter nisus at the Tyninghame Estuary, Firth of Forth, Scotland, provide an example of how the starvation–predation risk trade-off results in mortality. In this trade-off, animals cannot always optimize anti-predation behaviour because anti-predation behaviours, such as avoiding predators, are usually incompatible with foraging behaviours that might maximize intake rates. Therefore, as animals compensate for starvation risk, predation risk increases. Sparrowhawks are the main direct cause of death in Redshanks at Tyninghame. Sparrowhawk attack rate is determined by Redshank vulnerability, and vulnerability decreases as group size and distance to cover increase, and probably as spacing decreases. But reduction of predation vulnerability reduces feeding rate because areas away from cover are less food-profitable and grouping results in increased interference competition. Increased starvation risk in midwinter means Redshanks are forced to feed on highly profitable prey, Orchestia amphipods, the behaviour of which means that Redshanks are forced to feed vulnerably, in widely spaced groups, close to predator-concealing cover. Therefore, it is the constraints that limit the ability of Redshanks to feed in large, dense flocks away from cover that ultimately lead to mortality. We investigate this hypothesis further by testing the prediction that mortality can be predicted directly by cold weather and population density. We demonstrate that the overall number of Redshanks and the proportion of Redshanks killed increase in cold months when controlling for population size. We also demonstrate that the proportion of Redshanks killed increases when there are fewer Redshanks present, because the success rate of hunting Sparrowhawks increases, probably because effective management of predation risk through flocking is constrained by a low population size. Redshanks therefore provide an example of how directly mortality caused by predation arises from starvation risk and other constraints that prevent animals from optimizing anti-predation behaviour.
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Most physiological and ecological approaches to animal locomotion are based on steady state assumptions, yet movements of many animals are interspersed with pauses lasting from milliseconds to minutes. Thus, pauses, along with changes in the duration and speed of moves, form part of a dynamic system of intermittent locomotion by which animals adjust their locomotor behavior to changing circumstances. Intermittent locomotion occurs in a wide array of organisms from protozoans to mammals. It is found in aerial, aquatic and terrestrial locomotion and in many behavioral contexts including search and pursuit of prey, mate search, escape from predators, habitat assessment and general travel. In our survey, animals exhibiting intermittent locomotion paused on average nearly 50% of their locomotion time (range 6-94%). Although intermittent locomotion is usually expected to increase energetic costs as a result of additional expenditure for acceleration and deceleration, a variety of energetic benefits can arise when forward movement continues during pauses. Endurance also can be improved by partial recovery from fatigue during pauses. Perceptual benefits can arise because pauses Increase the capacity or the sensory systems to detect relevant stimuli. Several processes, including velocity blur, relative motion detection, foveation, attention and interference between sensory systems are probably involved. In animals that do not pause, alternative mechanisms for stabilizing the perceptual field are often present. Because movement is an important cue for stimulus detection, pauses can also reduce unwanted detection by an organism's predators or prey. Several models have attempted to integrate energetic and perceptual processes, but many challenges remain. Future advances will require improved quantification of the effects of speed on perception.
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Peregrine Falcon Falco peregrinus hunting behaviour was studied at nest-sites in three areas of South Africa over eight years. In Africa, resident Peregrines are mostly restricted to high cliffs, possibly because these structures provide optimal conditions for hunting. This hypothesis is examined in terms of the influence of nest-site quality, particularly cliff height, on foraging efficiency. Foraging mode varied considerably between sites, and males foraged more actively than females but there was little variation in the design of hunts between sexes, seasons or study areas. Individually, Peregrines spent 30-50% of the day on or near the nest cliff. On average, about 0.5 hunts were recorded per hour of observation. Foraging mode was not correlated with cliff height or elevation above the surrounding terrain, but Peregrine pairs occupying higher cliffs achieved greater hunting success rates. Most hunts were initiated from elevated perches on the nest cliff, and perch hunts were more successful than strikes made from the air. Success was highest in strikes at doves and small passerines, and over habitats with moderate cover. The height difference between Peregrine and prey at the start of a hunt positively and significantly affected hunting success. Overall, Peregrines were relatively sedentary and made extensive use of the nesting habitat as a foraging area. High nest cliffs contributed to foraging success by providing perch-hunting falcons with an effective height advantage over their prey.
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The ability of Marsh Hawks (Circus cyaneus) to locate prey acoustically was measured in both the laboratory and the field. Laboratory experiments indicated that the directional hearing of the Marsh Hawk was substantially better than that of a sample of typical diurnal raptors and similar to that of owls capable of capturing prey in total darkness. Angular resolution along the horizontal axis was 2° for the Marsh Hawks, 1-2° for the owls, and 8-12° for the sample of typical diurnal raptors. For the Marsh Hawks, angular resolution along the vertical axis was at least 2°. The maximum range at which prey could be detected by sound was estimated to be 3-4 m for the Marsh Hawk and 7 m for the Barn Owl (Tyto alba). Field experiments indicated that free-ranging Marsh Hawks could locate vole vocalizations (squeaks) accurately and attack prey successfully without the aid of visual or olfactory cues. Additional field experiments were conducted to determine how the Marsh Hawk integrates auditory and visual cues while capturing concealed prey. These experiments show that the Marsh Hawk does not require motion cues or auditory depth perception to determine the elevation of a sound source.
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Suggests how differences in sensory modality can play a primary role in shaping the foraging behavior, specifically foraging height, of a raptor guild in open-field areas of west-central Oregon (red-tailed hawk Buteo jamaicensis, rough-legged hawk B. lagopus, white-tailed kite Elanus leucurus, American kestrel Falco sparverius and marsh hawk Circus cyaneus) which exploits the same prey base, viz. mountain vole Microtus montanus.-P.J.Jarvis
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In a dry thornscrub area of N Spain during the breeding season, wheatears were more diverse in their foraging mode mainly using perch-to-ground sallying and running ground-gleaning. Stonechats were sallying specialists. Wheatears on average used lower perches than stonechats. The distributions of successful and unsuccessful search times for both species resemble log-normal distribution. Departures from both types of perches occurred independently of the time already spent on the perch. Stonechats generally stayed longer on perches, and had lower departure rates from them than wheatears. Capture probabilities were lower for stonechats. Giving-up times and successful search times increased with perch height, and were longer for stonechats at the same perch heights. This suggests that these birds were able to estimate how long it would take to search the area viewed from each perch, and that the height of the perch and probably the complexity of the area determine these giving-up times. The return-to-perch rate of stonechats was twice that of wheatears. The return rate was negatively correlated with search times preceding the previous sally for wheatears, but not for stonechats. Wheatears generally moved longer between perches than stonechats. Size of the detection area from a perch thus determines the subsequent distance moved after giving up. -from Author
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The different searching tactics of passerine birds foraging for arthropods among the foliage of a northern hardwoods forest result in the capture of different kinds of prey. Five major searching modes are employed by the 11 foliage-foraging bird species in the Hubbard Brook Experimental Forest, New Hampshire. These are distinguished primarily by the rates and distances moved by the searching birds and by the types and forms of their prey-attacking maneuvers. These in turn reflect how large an area is scanned, how thoroughly it is searched, and how the bird moves from perch to perch in its search for prey. Mean searching and prey-attacking flight distances are positively correlated, indicating that birds move just far enough on average to take them into areas they have not previously searched visually. Likewise, birds that move rapidly while searching make significantly more prey attacks per unit time and hence encounter prey more often. Slow searchers scrutinize substrates more thoroughly and seem to take more cryptic and often larger prey. The results suggest that there are limitations on the ways that birds can search for and capture arthropod prey among foliage. We hypothesize that constraints imposed by the structure of the vegetation and by the types and abundances of prey determine the available foraging opportunities. Such habitat parameters may affect, in ecological or evolutionary time, the foraging traits of birds that can successfully exploit a particular habitat, and hence influence the patterns of bird habitat selection and community structure.
Article
A major factor influencing the quality of raptor habitats is food availability, which is determined not only by prey density, but also by various habitat features influencing the accessibility of prey. Many raptors hunt ground-living prey by using the energy-saving pause-travel search tactic. If perches to hunt from are lacking, a habitat may be difficult to exploit even if prey is abundant; hence perches are an important component of prey availability. The boreal forest landscape is drastically changed by very intensive forest management. Clearcuts, where mature forest has been harvested, are rich in prey (rodents) but lack perches. An experiment was performed to test if abundance of perches is a factor limiting the utilization of these habitats by foraging raptors. Eleven clearcuts were provided with man-made perches, and 11 clearcuts served as control. Foraging raptors used clearcuts with perches significantly more than clearcuts lacking perches, and raptor utilization changed accordingly when the control and experimental areas were switched.
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In north-Central Oregon, Red-tailed Hawks (Buteo jamaicensis) exhibited a high degree of stability in territory occupancy and territorial boundaries over a 10-yr period. Long-term reproductive success varied markedly among territories and was correlated primarily with the dispersion and density of perches used as foraging sites and secondarily with the abundance of ground squirrels, Principally the Belding's Ground Squirrel (Spermophilus beldingi). These results imply that prey availability is more important to reproductive success than absolute prey abundance. Pairs in territories with few or poorly dispersed perches did not rely more on energetically expensive aerial foraging. However, poor dispersion of perches resulted in both decreased flight time and in decreased foraging energy expenditure. Thus it is likely that Red-tailed Hawks in territories with few or poorly dispersed foraging perches deplete the prey near the perches that are present. Territory size was not correlated with reproductive success. Red-tailed Hawks coexisted with Swainson's Hawks, and showed strong interspecific territoriality. Some pairs of Red-tailed Hawks lost portions of their territories to the later arriving Swainson's Hawks each year. Yet the contention at territorial boundaries and loss of territory to Swainson's Hawks had no observable effect upon Red-tailed Hawk reproductive success.
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Nest loss in willow ptarmigan (Lagopus lagopus lagopus) was studied during 4 seasons on a small island in northern Norway. Territorial hooded crows (Corvus corone) were the most important nest predator. Nonterritorial crows, common ravens (Corvus corax), nesting black-billed magpies (Pica pica), and gulls (Larus spp.) were not important predators on willow ptarmigan eggs or on cryptically colored experimental eggs. Territorial crows located a larger proportion of willow ptarmigan nests within 350 m of their own nests than at 351-700 m. A similar predation pattern occurred for cryptically colored experimental eggs. One year, when the only nesting pair of crows was removed, nest loss decreased significantly. There was no relationship between nesting cover and nest loss. Territorial crows apparently located ptarmigan nests by watching hens' movements to and from their nests.
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Sparrowhawks Accipiter nisus, Peregrines Falco peregrinus and Merlins Falco columbarius were studied hunting Redshanks Tringa totanus, Dunlins Calidris alpina and Skylarks Alauda arvensis over three winters on a small Scottish estuary. Most Sparrowhawk and Merlin hunts consisted of a single attack (mean = 1.0 and 1.1, respectively), whereas Peregrine hunts often consisted of several attacks (mean = 1.8), Most hunts were short (<1 min), but Peregrine and Merlin hunts occasionally lasted over 5 min, In general, all three raptor species attacked by surprise, although Peregrines were more likely to make nonsurprise attacks. Prey attacked were usually initially very close to the raptor (<100 m); Peregrines attacked prey most often at long distances (>500 m). Chase lengths were mostly <5 second in length, although Peregrines, and particularly Merlins hunting Skylarks, often chased for several minutes. Peregrines attacked most prey in flight from night, while Merlins and Sparrowhawks attacked birds on the ground with a flight from a perch, All three raptor species preferentially attacked larger Dunlin necks, but Peregrines also favoured single birds, Capture rates of Redshanks and Dunlins were similar for the three raptor species (C, 10%), but for Skylarks, capture rate by Merlins was much higher (12%) than by Sparrowhawks (3%) or Peregrines (0%), Capture rates were highest when raptors attacked by surprise, particularly for a Peregrine hunting in the first minute of arrival on the study site if no Peregrines had been hunting there for the previous hour (16% success for the first minute compared with 2% in subsequent minutes), Sparrowhawks were more successful when attacking small rather than large Dunlin necks. The use of short surprise attacks interspersed with long periods of inactivity was common to the three raptor species and was interpreted as a strategy to minimize the amount of energy and risk involved in hunting during the nonbreeding season.