Article

Scavenging of Ruffed Grouse in the Appalachians: Influences and Implications

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Abstract

Scavenging is often neglected as a source of bias when determining causes of mortality and collecting mortality-related habitat information. The use of mortality-sensing radio-transmitters has greatly increased our understanding of animal survival. However, the potential of lag-time in recovery of carcasses and subsequent determinations of cause of death are seldom addressed. Motion created by feeding predators and scavengers can delay pulse switchover and prolong recovery. We determined the influence of temperature, forest stand type, overhead cover, and carcass condition on scavenging rates, displacement patterns, and habitat sampling biases at perceived kill sites for ruffed grouse (Bonasa umbellus). We documented carcass disturbance, scavenger species, and displacement distances for 64 carcasses. Mammalian scavengers disturbed 42 of 64 grouse carcasses. Scavenger species identified included mice (Peromyscus spp.), flying squirrel (Glaucomys spp.), cottontail rabbit (Sylvilagus floridanus), Virginia opossum (Didelphis virginiana), raccoon (Procyon lotor), long-tailed weasel (Mustela frentata), bobcat (Lynx rufus), eastern coyote (Canis latrans), and common raven (Corvus corax). Air temperature and carcass condition were the dominant factors associated with scavenger disturbance of grouse carcasses. Mammal scavenging activity increased during warmer temperatures, and mock avian kills were scavenged more frequently than whole carcasses. Potential overestimation of mammalian-caused mortality may result from scavenging, especially when ambient air temperature is warmer and carcasses have been previously fed upon.

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... Studies of scavenger bias indicate that carcass size, carcass condition (partial vs. intact bodies), and ambient temperature explain variation in persistence (Bumann and Stauffer 2002, DeVault et al. 2004, Smallwood 2007, Flint et al. 2010. Equivocal results have been reported for the effect of local scale factors on carcass survival. ...
... Equivocal results have been reported for the effect of local scale factors on carcass survival. Bumann and Stauffer (2002) found no correlation between local habitat variables and time to removal, yet persistence varied among land-cover attributes in other studies (Pain 1991, DeVault et al. 2004, Santos et al. 2011. Some authors have speculated that correlations between local habitat factors and survival are explained by the activity and habitat preferences of local scavenger populations (Pain 1991, Santos et al. 2011. ...
... Our estimates of carcass survival could have been influenced by carcass condition. Carcasses placed at buildings were whole and intact, which may have increased persistence rates (Bumann andStauffer 2002, Smallwood 2007). In addition, carcasses were frozen prior to use in scavenger trials, and freezing may decrease carcass detection and attractiveness by altering olfactory signals and extending survival rates (Bumann and Stauffer 2002, Smallwood 2007, Smallwood et al. 2010. ...
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Collisions with windows remain an important human-related threat to bird survival in urban landscapes. Accurately estimating the magnitude of avian mortality at windows is difficult and may be influenced by many sources of error, such as scavenging of carcasses. Failure to account for removal of carcasses by scavengers can bias estimates of window mortality. We tested the hypothesis that carcass survival depends on local habitat factors known to influence scavenger behavior. Scavenger activity on bird carcasses was documented at 20 buildings in an urban landscape in northwestern Illinois for 1 week during each season of a year. Known-fate models were used to relate carcass survival to local habitat composition and to evaluate temporal variation in survival. We also documented species of scavengers and the timing of scavenging using motion-triggered cameras. Daily carcass survival was greater in winter than during spring, summer, and fall. Survival was related negatively to canopy cover (trees and shrubs within a 50-m buffer) and window area, and positively to pavement cover. Using an exponential model of survival time, estimated mean time of survival of carcasses (t± SE) was 82.9 ± 11.7 d for winter and 11.8 ± 7.2 d for other seasons. Raccoons (Procyon lotor) scavenged more carcasses than other species. Our results suggest that (1) carcass survival times may be short at locations with preferred habitats of known scavengers and predictable sources of food, and (2) knowledge of scavenger distribution and activity can inform predictive models of persistence. In studies of bird-window collisions, the influence of scavenger bias can be minimized by maintaining short time intervals between carcass searches. Search intervals can be inferred by estimating the number of days that a carcass should persist at a site, which can be calculated using predicted daily survival probabilities of carcasses at study buildings.
... Death was classified as exposure if no trauma was found on the carcass or transmitter. This category may be underestimated if chicks were scavenged post-death but before we discovered the carcass (Bumann & Stauffer 2002). Chicks presumed to experience heightened mortality risk due to handling were not included in estimates of survival, nor probable causes of natural mortality. ...
... We speculate that heavy losses in a single year presumably could occur if a prolonged period of wet and cold weather persisted (2-3 days) through the early stages of chick growth before chicks are able to thermoregulate (Bousquet & Rotella 1998). Assigning the cause of mortality for marked chicks or hens has subjective bias that is difficult to eliminate (Bumann & Stauffer 2002). Chicks dead from exposure were presumably available for scavenging before recovery and, therefore, we may have underestimated exposure kills. ...
... Chicks dead from exposure were presumably available for scavenging before recovery and, therefore, we may have underestimated exposure kills. Moreover, secondary predation events can obscure evidence between predator types (Bumann & Stauffer 2002). We attempted to guard against bias in predator identification by recording kills as 'unknown predator' if evidence was contradictory or insufficient. ...
Article
We studied survival and probable causes of mortality for plains sharp-tailed grouse Tympanuchus phasianellus jamesi chicks up to 30 days of age, and for hens during the reproductive period in Alberta, Canada, during 1999-2001. We used the Kaplan-Meier function for estimating survival for >1 radio-marked chick in the same brood and a bootstrapping technique to calculate standard errors while accounting for censored data. Chick survival was 47% over two years (95% CI: 29-64%) with 81% of mortalities occurring during the first 15 days. Predation accounted for 72% of chick mortalities with mammals taking the largest portion. Chick survival was similar when compared between landscapes with <35% vs ≥35% crop and sparsely covered grassland (8 km2). Hen survival was 53% (95% CI: 44-63%) during the reproductive period over three years. Most hen mortalities were from predation (96%), with mammals accounting for the largest portion followed by raptors. Hen survival was similar in landscapes (8 km2) with <35% crop and sparsely covered grasslands compared with those in areas with ≥35%. Our study helps clarify values of two critical vital rates, i.e. early chick survival and hen survival over the reproductive period.
... The scavenging guild of BPF was relatively efficient at locating ungulate carcasses irrespective of the season, habitat or carcass type. Carcass visibility, in relation to habitat types, had no influence on how fast scavengers located carcasses in North American forests (Bumann & Stauffer 2002, DeVault & Rhodes 2002, but did affect it in Camargue marshes (Pain 1991). In other studies, the survival times of different types of carcasses were highly variable. ...
... In other studies, the survival times of different types of carcasses were highly variable. Carcasses of rodents (Simonetti et al. 1984, DeVault & Rhodes 2002, small birds (Tobin & Dolbeer 1990, Linz et al. 1991, Kostecke et al. 2001) and grouse (Bumann & Stauffer 2002) had a relatively long survival time, whereas wildfowl carcasses at wintering concentration places were quickly discovered (78-100% within 24 h) , Peterson et al. 2001. It thus seems that the carcass survival time is related to the predictability of the carcass supply which, when high, may favour the acquisition of evolutionary adaptations by the scavenger species to locate the food resource. ...
... Skagen et al. (1991) observed that avian scavengers, particularly bald eagles, showed a strong preference for feeding stations far away from shoreline vegetation. By contrast, medium-sized carnivores seemed to seek dense shrub cover when consuming carrion (Bumann & Stauffer 2002) and whenever possible they removed parts of the carcass inside thickets to consume them there. The raccoon dog, a slow clumsy animal often killed by larger predators, attended bison carcasses placed in the forest significantly more ...
... Although most studies estimating carcass retention only considered carcass survival as a function of time, several studies have evaluated the influence of other factors. Bumann and Stauffer (2002) suggested that birds with exposed viscera likely provided stronger olfactory stimulus to scavengers. One study using songbird carcasses reported differences in carcass retention among different habitat types (Kostecke et al. 2001). ...
... We banded all carcasses for individual identification prior to field placement to aide in monitoring. To prevent scavenging bias associated with unrealistic carcass presentation (Bumann and Stauffer 2002), we removed feathers from the front of the breast of each carcass and made 2 perpendicular 4-cm incisions, centered where the feathers were removed from the breast, to simulate collision with a barbed-wire fence. We placed carcasses in coolers on ice until field placement. ...
... accessed 12 Jan 2009) to generate random fence points >200 m apart in each habitat type. Bumann and Stauffer (2002) placed ruffed grouse carcasses >100 m apart in their Appalachian study, however, sagebrush-steppe habitats are more open than deciduous forest, so larger inter-carcass distances are likely necessary. Therefore, we ensured that carcass locations were !200 m apart. ...
Article
We used female ring-necked pheasant (Phasianus colchicus) carcasses as surrogates for greater sage-grouse (Centrocercus urophasianus) to study factors influencing survival and detection bias associated with avian fence collision surveys in southern Idaho, USA, during spring 2009. We randomly placed 50 pheasant carcasses on each of 2 study areas, estimated detection probability during fence-line surveys, and monitored survival and retention of carcasses and their associated sign over a 31-day period. Survival modeling suggested site and habitat features had little impact on carcass survival, and constant survival models were most supported by the data. Model averaged carcass daily survival probability was low on both study areas and ranged from 0.776 to 0.812. Survival of all carcass sign varied strongly by location, and the top sign survival model included a site effect parameter. Model averaged daily survival probability for collision sign on the 2 study sites ranged from 0.863 to 0.988 and varied between sites. Logistic regression modeling indicated detection probability of carcasses during fence-line surveys for avian collision victims was influenced by habitat type and microsite shrub height at the carcass location. Carcasses located in big sagebrush (Artemisia tridentata) habitats were detected at a lower rate (0.36) than carcasses in little (A. arbuscula) and black sagebrush (A. nova) habitats (0.71). Increasing shrub height at the carcass location from the little sagebrush mean of 16.5 cm to the big sagebrush mean of 36.0 cm reduced detection probability by approximately 30%. Avian fence collision surveys in sagebrush-steppe habitats should be conducted at ≤2-week sampling intervals to reduce the impact of survival bias on collision rate estimates. Two-week sampling intervals may be too long in areas with low carcass and sign survival, therefore survival rates should be estimated on all study areas to determine the appropriate sampling interval duration. Researchers should be aware of the effects of local vegetation on detection probabilities, and methods to correct detection probabilities based on collision site attributes should be applied to ensure more accurate collision rate estimates. Additionally, caution should be used when aggregating or comparing uncorrected collision data from areas with differing vegetation, as detection probabilities are likely different between sites. © 2011 The Wildlife Society.
... We use camera traps to identify the scavenger guild, as they have been successfully used to monitor carcass removal experiments elsewhere (e.g. Bumann & Stauffer, 2002;Smallwood, Bell, Snyder & Didonato, 2010). ...
... Scavenging was intermediate in the second trial, which started in cool, wet weather. Air temperature has previously been reported to affect scavenging, with cold weather reducing scent dispersal and scavenger activity (Bumann & Stauffer, 2002). This declining interest among scavengers could also be evidence of scavenger swamping, but we suggest the temperature is more likely to have affected scavenging behaviour because all carcasses were eaten in the latter days of the later trials. ...
... Scavenging studies have traditionally focused on the role of competitive or social factors on carcass exploitation by scavengers (e.g., Wallace and Temple 1987;Heinrich 1988;Travaini et al. 1998). Recently, however, a few studies have investigated the proportion of carcasses consumed by a guild of scavengers or a certain species, as well as the environmental factors affecting the use of carrion (Bumann and Stauffer 2002;DeVault and Rhodes 2002;Selva et al. 2003;DeVault et al. 2004). Those studies have emphasized the role of habitat in segregating scavengers, or of ambient temperature as the main factor mediating competition among vertebrate scavengers and decomposers. ...
... In conclusion, carcass use by facultative scavengers in a natural temperate forest was not random. It was a prevalent and complex process determined by both extrinsic factors, as also shown by other studies (Bumann and Stauffer 2002;DeVault et al. 2004), and behavioural adaptations of the scavengers. The traditional concept of facultative scavenging as sheer opportunism may be misleading. ...
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Although facultative scavenging is very common, little is known about the factors governing carrion acquisition by vertebrates. We examined the influence of carcass characteristics, carcass state, and weather conditions on carrion use by main scavengers. Carcasses (N = 214, mainly ungulates) of various origins (predation, natural deaths, harvest) were monitored by systematic inspections (N = 1784) in Białowieża Forest (Poland). Common raven (Corvus corax L., 1758), red fox (Vulpes vulpes (L., 1758)), and European pine marten (Martes martes (L., 1758)) mainly used the prey remains of gray wolves (Canis lupus L., 1758). The kills of predators were the preferred carrion, rather than dead ungulates. Common ravens, common buzzards (Buteo buteo (L., 1758)), white-tailed eagles (Haliaeetus albicilla (L., 1758)), and domestic dogs scavenged more frequently on carcasses in open habitats. Carcasses located in the forest were the most available to European pine martens, jays (Garrulus glandarius (L., 1758)), and wild boar (Sus scrofa L., 1758). The common tendency was to increase scavenging when temperature decreased, except for raccoon dogs (Nyctereutes procyonoides (Gray 1834)). As snow depth increased, jays and great tits (Parus major L., 1758) increased scavenging. We suggest that carrion use by scavengers is not random, but a complex process mediated by extrinsic factors and by behavioural adaptations of scavengers.
... Although most studies estimating carcass retention only considered carcass survival as a function of time, several studies have evaluated the influence of other factors. Bumann and Stauffer (2002) suggested that birds with exposed viscera likely provided stronger olfactory stimulus to scavengers. One study using songbird carcasses reported differences in carcass retention among different habitat types (Kostecke et al. 2001). ...
... Pain (1991) reported mallard (Anas platyrhynchos) carcass longevity was significantly lower for exposed carcasses than those concealed by vegetation. In contrast, Bumann and Stauffer (2002) found no relationships between scavenging of ruffed grouse (Bonasa umbellus) carcasses and habitat characteristics. ...
... Scavenging by small or medium-sized herbivores may appear unlike- ly, owing to the increased mortality risk and encounter rates with predators expected near carcasses (Cortés-Avizanda and others 2009). However, carrion use, even by herbivores such as Eastern Cottontail (Sylvilagus floridanus) and Beaver (Castor canadensis) ( Bumann and Stauffer 2002;Gleason et al. 2005), has been increasingly documented. These foraging strategies may represent limitations in preferred food sources (Needham and others 2014), strategic acquisition of limiting nutrients (e.g. ...
... Although it is difficult to relate estimates of scavenging frequency to any measure of ecolog- ical importance or mechanism, these observa- tions at least demonstrate that the behaviour is a regular occurrence for hares, and individuals will consume carrion from a variety of different species. This is especially true relative to other lagomorph species, as despite numerous field studies on scavenger community dynamics in the eastern United States (DeVault and Rhodes 2002;DeVault and others 2004;others 2012, 2016;Smith and others 2017;Turner and others 2017), cottontail rabbits (Sylvilagus spp.) have only been observed scavenging on 1 occasion ( Bumann and Stauffer 2002). We recommend further research be conducted on scavenging in Snowshoe Hares in order to understand the factors that lead to its occur- rence. ...
... Cause-specific mortality was primarily mammalian, although, using marks on the transmitter as a diagnostic tool, I may have over-estimated this cause of mortality. Bumann and Stauffer (2002) argued that survival studies reporting cause-specific mortality typically overestimated mammalian-caused mortality due to scavenging of the carcass. By analyzing remote cameras at ruffed grouse carcasses in Virginia, they estimated 100% of carcasses were scavenged in > 5 days. ...
... Ĩ . 117 remote cameras (Bumann and Stauffer 2002). Because nest success appeared high, chick survival (Chapter 3) and juvenile survival needs to be examined as mechanisms limiting this population Braun 1997, Connelly et al. 2000b). ...
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Thesis (M.S.)--University of Idaho, 2003. Ch. 1. Nest site selection and success of greater sage-grouse in northwest Colorado -- ch. 2. An evaluation of the timing of greater sage-grouse nest vegetation sampling -- ch. 3. Nocturnal and diurnal habitat selection of greater sage-grouse during brood-rearing in northwest Colorado. Includes bibliographical references.
... Incorrect predator classification can introduce bias into telemetry studies when scavengers obscure evidence from the original predator, and inflate estimates of mortality due to predation if animals that die due to factors other than predation, such as disease, are misclassified as a result of scavenging activity (Larsen and others 2008). Similar to previous studies, we observed high levels of scavenging activity on gamebird carcasses in eastern Montana that would result in incorrect classification of cause-specific mortality (Dumke and Pils 1973;Bumann and Stauffer 2002;Larsen and others 2008), with rates of scavenging that were significantly greater in summer than spring. ...
... Avian scavengers in our study area, such as the Northern Harrier, typically pluck and consume prey on the ground, whereas it could be easier for larger-bodied mammals to move or cache a carcass (Harrington 1982; Thogmartin and Schaeffer 2000; Smith and others 2011). Misclassification of cause-specific mortality may be higher in areas where mammals are the primary scavengers (Bumann and Stauffer 2002). Therefore, both the scavenger assemblage and the timing of the study should be considered when applying our results to other locations. ...
Article
Survival estimation is critical to studies of wildlife population biology and recent model developments allow for temporal covariates on mortality risk. To test model assumptions that scavengers do not influence either perceived mortality cause or location, we placed 24 radio-marked Chukar (Alectoris chukar) carcasses randomly over gradients of grassland habitat conditions in eastern Montana in both April 2017 and July 2018, and monitored scavenging activity at intervals relevant to gamebird telemetry studies. High rates of scavenging (12.5–78%, depending on season and relocation interval) suggest that scavenging activity could confound determination of cause-specific mortality but that its influence varies with season. Scavenging activity did not significantly influence perceived mortality locations regardless of season or local habitat conditions with a relocation interval of 3 d (8% of carcasses moved), but mortality locations may be biased over longer periods (50% of carcasses moved in 7-d period), particularly in warm seasons or regions.
... In studies assessing the fate of smaller carcasses, removal has typically been higher (e.g. Bickart, 1984; Balcomb, 1986; Bumann & Stauffer, 2002; DeVault et al., 2004). In experiments conducted near the experimental site in August 2000 (involving 38 bird carcasses weighing between 9 and 420 g), higher scavenger removal of smaller birds than of larger birds was observed (Brown, 2000). ...
... The increased scavenger-effect in summer 2001 may have been related to higher temperatures as well as the drought-related dietary stress of facultative scavengers. Temperature has been noted elsewhere as having an effect on scavenging by: (1) affecting the discovery rate of carcasses due to the accelerated onset and increased intensity of olfactory cues; (2) altering the amount of invertebrate activity in competition with vertebrate scavenging and the time until bacterial generation of toxicity; and (3) influencing the activity of scavenging reptiles (Guarino, 2001; Bumann & Stauffer, 2002; DeVault & Rhodes, 2002; Selva et al., 2003; DeVault et al., 2003). The overall effect of higher temperatures is generally towards both earlier onset, and earlier cessation, of scavenging by vertebrates. ...
Article
Scavenging is one of the primary taphonomic processes shaping the final composition of fossil faunal assemblages. The taphonomic effect of scavengers is variable and must be understood in the context of the causes of that variation. In this study, we investigated relationships between the El Niño Southern Oscillation (ENSO), variable rainfall and scavenging on 20–40 kg mammal carcasses in semi-arid New South Wales over four years. Following periods of above-average rainfall (coincident with the La Niña phase of the ENSO), there was an increased availability of non-carrion food and scavenging activity was moderate. Following below-average rainfall (coincident with the El Niño phase of the ENSO), foraging options diminished, leading to a greater importance of carrion in the diet of scavengers and a resultant increase in carcass disturbance, transport and destruction by scavengers. Feral pigs (Sus scrofa) and red foxes (Vulpes vulpes) were the most taphonomically significant scavengers in the study. Australian ravens (Corvus coronoides) and wedge-tailed eagles (Aquila audax) were active scavengers throughout the period of the study, but had little impact on bone survival. Lace monitors (Varanus varius) also fed mostly on soft tissue and were only present seasonally. We found that climate variability in the form of short-term oscillation can result in significant variation in the impact of scavengers on carcasses and may be an important consideration when evaluating site formation scenarios and biases in fossil faunal assemblages. Copyright © 2006 John Wiley & Sons, Ltd.
... When we located a carcass or kill site, we classified the probable cause of mortality as mammal, avian, snake, hunter, accident, or unknown based on evidence at recovery sites. It is difficult to make unambiguous statements about causes of mortality (Bumann and Stauffer 2002), and we refer to ''probable causes of mortality'' in this article. We attempted to minimize confounding effects of scavenging by recovering of transmitters emitting a mortality pulse in 24 hours. ...
... The possibility of mammalian scavenging makes predator classification from evidence at kill sites problematic (Bumann and Stauffer 2002). However, if a bias occurred in this study it was likely consistent across age classes and study sites. ...
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ABSTRACT Long-term population declines and habitat reductions have increased concern over the status of the lesser prairie-chicken (Tympanuchus pallidicinctus). Robust estimates of demographic parameters are essential for identifying population declines and planning effective management. We evaluated the effects of age and season on the survival of female lesser prairie-chickens at 2 sites in southwestern Kansas, USA. Using telemetry data from a 7-year field study (from 1997 to 2003), we estimated seasonal (Apr—Sep) and annual (Apr—Mar) survival. We also examined daily survival rates of females attending nests during the 26-day incubation period and young during the 14-day early brood-rearing period. We evaluated the probable mortality causes of radiomarked birds by examining evidence at recovery sites. We captured 227 female lesser prairie-chickens (87 yearlings, 117 ad, and 23 age undetermined) and fitted them with radiotransmitters. Estimates of 12-month survival were lower among yearlings (Ŝ12 = 0.429, SE = 0.117) and adults at site I (Ŝ12 > = 0.302, SE = 0.080) than among yearlings (Ŝ12 = 0.588, SE = 0.100) and adults at site II (Ŝ12 > = 0.438, SE = 0.083). The patterns in timing of mortality and age-specific 6-month survival were consistent with those of 12-month estimates at site I from 1998 to 2002, with a peak in mortality during May and June. Females tending to nests or to prefledged chicks had lower daily survival (DŜRtend = 0.993, SE = 0.001) than females not involved in these activities (DŜRfailedbreeder = 0.997, SE = 0.002). We recorded 92 mortalities from April 1997 to March 2003, and 59% and 11% were attributed to predation by mammals and raptors, respectively. Our research suggests that predation during the nesting season can have a major impact on lesser prairie-chicken demography, and conservation efforts should focus on enhancing female survival during the nesting and brood-rearing seasons.
... We classified sparrows as dead when the carcass was found or when the transmitter or harness demonstrated evidence that the sparrow had been killed (e.g., bite marks). Bumann and Stauffer (2002) concluded that assigning a source of mortality based on physical evidence at the site of the recovered radiotransmitter might be problematic. We recognize this potential source of error and took the following precautions in assigning source of mortality. ...
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Wintering Henslow's sparrow (Ammodramus henslowii) populations rely on lands managed with prescribed burning, but the effects of various burn regimes on their overwinter survival are unknown. We studied wintering Henslow's sparrows in coastal pine savannas at the Mississippi Sandhill Crane National Wildlife Refuge, Jackson County, Mississippi, USA, during January and February 2001 and 2002. We used the known-fate modeling procedure in program MARK to evaluate the effects of burn age (1 or 2 growing seasons elapsed), burn season (growing, dormant), and calendar year on the survival rates of 83 radiomarked Henslow's sparrows. We found strong evidence that Henslow's sparrow survival rates differed by burn age (with higher survival in recently burned sites) and by year (with lower survival rates in 2001 likely because of drought conditions). We found some evidence that survival rates also differed by burn season (with higher survival in growing-season sites), although the effects of burn season were only apparent in recently burned sites. Avian predation was the suspected major cause of mortality (causing 6 of 14 deaths) with 1 confirmed loggerhead shrike (Lanius ludovicianus) depredation. Our results indicated that recently burned savannas provide high-quality wintering habitats and suggested that managers can improve conditions for wintering Henslow's sparrows by burning a large percentage of savannas each year.
... Cause of death was ascribed to raptor predation if the carcass was cleaned of soft tissue with the skeleton remaining intact or to mammal predation if bones were crushed, tooth marks appeared on the transmitters, or tracks identified a mammal as the possible author of a death (Curtis et al. 1988). It was impossible to separate scavenging by mammals from killing by mammals; scavenging may result in overestimates of mortality due to mammals (Bumann and Stauffer 2002). Other causes of death included natural mortality (carcass intact), entanglement of the neck loop of the radio, hunting, and prescribed fire. ...
Article
We assessed supplemental feeding in a crossover design to determine its value in managing the dispersion and mortality of northern bobwhites (Colinus virginianus) in Roberts County, Texas Panhandle, during October–March 2000–2001, 2001–2002, and 2002–2003. Nontarget species made up 98% of feeder visits (n=152 visits in 480 hours of surveillance). The average home range (ha) on the fed site was 34% of that on the control site (95% CL=21–48%) in 2001–2002 and 63% (39–103%) in 2002–2003, suggesting that feeders localized coveys. Fall-spring survival estimates were 0.57 (0.40–0.73) on the fed site versus 0.72 (0.53–0.91) on the control site in 2001–2002; estimates were 0.24 (0.16–0.33) on the fed site versus 0.28 (0.22–0.34) on the control site in 2002–2003, indicating null effects of feeding on fall-spring survival. Apparent vulnerability of bobwhites to loss sources (avian or mammalian predators, other losses) was not affected by feeding. Based on our results, managers who wish to localize coveys could accomplish that objective using feeders; otherwise, food supplementation was a neutral management practice.
... Avian predators were the leading cause of predation, followed by mammalian predators and unidentified predators. We assigned mortality agents based on inspection of carcass remains and signs surrounding the relocated carcass or radiotransmitter, but Bumann and Stauffer (2002) concluded scavenging by mammalian predators altered field evidence of avian predation. Consequently, our results represent a minimum estimate of avian predation and a maximum estimate of mammalian predation. ...
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The Appalachian Cooperative Grouse Research Project (ACGRP) was a multistate cooperative effort initiated in 1996 to investigate the apparent decline of ruffed grouse (Bonasa umbellus) and improve management throughout the central and southern Appalachian region (i.e., parts of Ohio, Pennsylvania, Rhode Island, Kentucky, West Virginia, Virginia, and North Carolina, USA). Researchers have offered several hypotheses to explain the low abundance of ruffed grouse in the region, including low availability of early-successional forests due to changes in land use, additive harvest mortality, low productivity and recruitment, and nutritional stress. As part of the ACGRP, we investigated ruffed grouse population ecology. Our objectives were to estimate reproductive rates, estimate survival and cause-specific mortality rates, examine if ruffed grouse harvest in the Appalachian region is compensatory, and estimate ruffed grouse finite population growth. We trapped >3,000 ruffed grouse in autumn (Sep-Nov) and spring (Feb-Mar) from 1996 to September 2002 on 12 study areas. We determined the age and gender of each bird and fitted them with necklace-style radiotransmitters and released them at the trap site. We tracked ruffed grouse ≥2 times per week using handheld radiotelemetry equipment and gathered data on reproduction, recruitment, survival, and mortality.
... Our findings also suggest that collisions with man-made structures may be additive to other mortality factors, and recruitment in years of poor reproduction may not be adequate to offset low survivorship. Since scavenging, especially by mammals, can occur at over 50% of carcasses within days (Bumann and Stauffer 2002), it is likely that collisions with fences or powerlines are occurring at a rate even higher than we are reporting. Elsewhere, collisions with fences and powerlines have been estimated to be one the greatest mortality factors for grouse in Scotland and Norway (Baines and Andrew 2003, Baines and Summers 1997, Bevanger 1995). ...
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Project Objectives: The objectives of this study are to address potential causes of declines in the Lesser Prairie-Chicken (Tympanuchus pallidicinctus) through examination of habitat use, nesting success, and mortality rates via capture and radio-tracking of marked wild birds in western Oklahoma. Included is a comparison of these factors among dry-land cultivated, irrigated cultivated, native rangeland, introduced grass non-CRP pasture, native-mix CRP pasture, and Old World Bluestem CRP pasture, and across seasons for three years beginning July 2000.
... In investigations where carcases need to be collected for examination, scavenging and disturbance by wild, feral and domesticated animals can hamper collection of bodies and make counting difficult (Bumann & Stauffer 2002). In ecological studies the use of dogs has been advocated in order to increase the rate of recovery of carcases (Homan et al. 2001). ...
Article
Wildlife crime, defined here as the illegal taking, disturbance, possession, trade or movement of animals and or their derivatives, is a growing international problem that threatens the survival of many species. In the investigation of such incidents the 'crime scene' may range from the carcass (or parts) of an animal to terrain that encompasses topography as varied as forest or desert and which may include diverse natural and man-made structures. Often, the location of the wildlife crime scene is isolated, with few facilities for proper investigation and collection of evidence. In poorer parts of the world and in countries experiencing social unrest, these features may present particular challenges. Wildlife crime scene work is such that equipment, investigative techniques and scientific technology all need to be appropriate to, and the best available in, the circumstances. Effective investigation under field conditions is likely to require a combination of portable and easy-to-use laboratory equipment coupled with modern methods of data collection and information transmission. An interdisciplinary approach is essential. Biologists/naturalists and those experienced in health studies, especially epidemiology, can often usefully complement the role of the police, enforcement officials and crime scene specialists.
... awks (Buteo jamaicensis), red-shouldered hawks (Buteo lineatus) broad-winged hawks (Buteo platypterus), Cooper's hawks (Accipiter cooperii), and great horned owls (Bubo virginianus) are important grouse mortality causes (Bumann and Stauffer 2004). However, evidence at our mortality sites showed mammalian predation accounted for the greatest losses. Bumann and Stauffer (2002) found mammals scavenged >65% of placed grouse carcasses and warned of overestimating mammalian predation based on mortality site evidence. The narrow margin between mammalian and avian predation on WSC may have resulted from such bias. Survival estimates did not differ between juveniles and adults, indicated by lack of age effect in sur ...
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Sound management of ruffed grouse ( Bonasa umbellus) populations requires an understanding of survival and cause-specific mortality; how - ever, these parameters have not been investigated at the southern extent of the species' range. Ruffed grouse were studied in the mountains of western North Carolina. Grouse (n = 276) were radiotagged and monitored >3 times/week. Mean annual survival was greater than reports from the northern core of the species' range. Seasonal survival was greatest in summer, followed by fall, winter, and spring. Of 155 mortalities, the greatest proportion was attrib- uted to mammalian, followed by avian, and unknown predation, hunter harvest, and other. Scavenging prior to transmitter recovery may have positively biased mammalian predation rates. Despite long hunting seasons that extended into winter, hunter harvest rates were among the lowest reported in the literature. Population densities, estimated annually in spring, were 5.9-11.4 grouse/100 ha and showed no association with hunter harvest. Survival rates showed an inverse relation with population density. Lower survival when population density was greatest may be related to habitat availability.
... The majority of carcasses placed on roadsides by Antworth et al. (2005) were removed within 36 hr while Bumann and Stauffer (2002) reported a mean removal time of 68 hr with a minimum of 1 hr 46 min for dead grouse in Virginia. Removal of carcasses can be influenced by time of day, weather, temperature, species and condition of carcass, traffic density, topography, season, and species of predators (Bumann and Stauffer 2002; Slater 2002). Although our results did not indicate differences in removal time for different species of snakes, we did notice a significant difference in removal time by habitat type. ...
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Annually, millions of snakes are killed on roads in the United States. Because of their potential abundance and ease of collection, many researchers have used road-killed snakes to examine community composition, movement patterns, and population dynamics. However, few previous studies have accounted for snake carcasses that are removed from roads by scavengers. Snake carcasses were placed at randomly selected locations along 2 km of road, one traversing maritime forest and the other surrounded by dune habitat. Carcasses in forested habitat were removed more often (100% vs 40%) and more quickly (8 hr vs 11 hr) than those placed in dune habitat. Half of the carcasses (50%) were removed within eight hours of placement and all carcasses were removed at night. Species and size of carcasses did not affect removal time. Removal time and scavenging intensity of snake carcasses most likely varies across regions and habitats. Furthermore, because scavenging appears to occur quickly and to such a significant extent, it may confound results of studies examining patterns of road-mortality. Thus, investigators that use data from road-killed snakes would benefit from a concurrent investigation of scavenging and application of appropriate correction factors to avoid underestimation of snake mortality.
... We observed no change in the proportion of total mortalities attributed to mammalian predators, avian predators or collisions during the pre-and post-construction periods. However, our analyses of mortality are a relatively weak test for changes in cause-specific mortality rates because scavenging precludes unambiguous determination of cause of death (Bumann & Stauffer 2002;Larsen, Bentley & Flinders 2008). We are unable to discount the possibility that some prairie-chickens were killed by raptors, but scavenged by mammals before we located and inspected the carcasses. ...
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The potential effects of wind energy development on wildlife have received increased attention over the past decade. In Kansas, optimal sites for wind energy development often overlap with preferred habitats of greater prairie-chickens Tympanuchus cupido. Our goal was to determine whether wind energy development affected survival of female prairie-chickens in a grassland ecosystem, assessing one potential impact of wind on an upland gamebird of conservation concern. We focused primarily on the response of female prairie-chickens to wind energy development because population dynamics of prairie-chickens are primarily determined by female demography.We monitored prairie-chickens at a wind facility in Kansas during a 2-year pre-construction (2007–2008) and a 3-year post-construction period (2009–2011). We used data from 220 radio-marked females to calculate weekly survival and hazard rates. We used cause of death for 81 mortality events to test for changes in the proportion of mortalities attributed to mammalian predators, avian predators and collisions.We observed an unexpected increase in annual survival during the post-construction period (0·57) compared with the pre-construction period (0·32). Distance from home range centroid to the nearest wind turbine site had no effect on weekly survival of females. Collision mortality events were rare, and most were associated with fences or transmission lines and not turbine blades.Most female mortality was due to predation (c. 90%). Differences in annual survival were driven by a higher risk of mortality during lekking activity in March and April during the pre-construction period (weekly hazard rate = 0·050–0·062) compared with the post-construction period (hazard rate = 0·012–0·021). We observed no change in the proportion of mortalities attributed to different causes between the two treatment periods.Synthesis and applications. Development of a wind energy facility had no negative effect on survival of female prairie-chickens. The results of our field study indicate that greater prairie-chickens are less sensitive to wind energy development than lesser prairie-chickens Tympanuchus pallidicinctus and greater sage-grouse Centrocercus urophasianus are to oil and gas development. We have strong evidence that survival increased after wind energy development, and hypothesize that energy development affected the local predator community, resulting in an indirect effect of decreased predation risk during the post-construction period.
... Harvest mortality included radios recovered from birds shot by hunters, and occasional crippling mortalities where a bird was recovered dead during the hunting season with evidence of pellet damage to the transmitter or the body. In cases of natural mortality, we tried to determine cause of death from the carcass and associated sign at the kill site, recognizing that activity of scavengers can make it difficult to make unambiguous statements about causes of mortality (Hudson et al. 1997;Bumann & Stauffer 2002). Natural mortality events were classified as raptor predation if bird faeces were present, if the head or breast muscles were removed, or if feathers were plucked without evidence of chewing. ...
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1. The effects of harvest on the annual and seasonal survival of willow ptarmigan Lagopus lagopus L. were tested in a large-scale harvest experiment. Management units were randomly assigned to one of three experimental treatments: 0%, 15% or 30% harvest. Seasonal quotas were based on the experimental treatment and estimates of bird density before the hunting season. Survival rates and hazard functions for radio-marked ptarmigan were then estimated under the competing risks of harvest and natural mortality.
... Unlike Middle Bed I (Prassack, 2010), rodent gnawing is rare (0.002%). Some tooth scores are much smaller than expected for even small carnivores (Prassack, 2012) and may reflect predation or scavenging by rodents, as many are known to consume birds (Bumann and Stauffer, 2002;Jones et al., 2008). ...
Article
Plio-Pleistocene avifaunal communities are used to reconstruct Lowermost Bed II landscapes at the early hominin site of Olduvai Gorge, Tanzania. These deposits are laterally extensive, have strong chronostratigraphic control, and were excavated using a landscape archaeological approach. Such factors allow for horizontal spatial-correlation of avian communities across the paleolandscape over a geologically short time frame (approximately 65,000 years). Lowermost Bed II avifaunal communities point to an extensive freshwater wetland system across the extent of paleo-Lake Olduvai's eastern margin.
... A summary of studies using experimental carrion baits to measure scavenging efficiency showed that across all climates and localities, vertebrates consumed 75% of available carcasses (DeVault et al. 2003). Further, recent empirical studies using remote photography have demonstrated that many vertebrate species readily use carrion resources (Kostecke et al. 2001;Peterson et al. 2001;Bumann and Stauffer 2002;DeVault and Rhodes 2002). However, the competitive balance among scavengers and decomposers varies tremendously across ecosystem types and climate regimes (DeVault et al. 2003). ...
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Vertebrate scavengers and decomposers compete for animal carcasses in all temperate and tropical ecosystems. We examined the influence of carcass size, forest type, and air temperature on the fate of rodent carcasses at the Savannah River Site, South Carolina, USA. Three hundred rodent carcasses were placed at random locations in forested habitats and scavengers were identified using remote photography. Seventeen species of vertebrates removed 104 of 300 (35%) rodent carcasses over a year. Raccoons (Procyon lotor (Linnaeus, 1758)) and Virginia opossums (Didelphis virginiana Kerr, 1792) scavenged most frequently. For scavenged carcasses, the mean time to carcass removal was 2.58 days after placement. Carcass acquisition by scavengers and decomposers was influenced moderately by forest type and carcass size, although ambient air temperature considerably influenced the fate of carcasses. Vertebrates removed fewer carcasses as temperatures increased: only 28 of 144 (19%) carcasses were scavenged when temperatures exceeded 17°C. The temporal pattern of carcass removal by vertebrates, however, did not vary with temperature. Consistent rates of carcass removal by vertebrates across the year and increased activity by insects during warm weather led to elevated levels of decomposition during summer months. This study confirms the complexity and dynamic nature of competitive relationships among scavengers and decomposers.
... When a transmitter's signal indicated mortality, we located and recovered the transmitter from the ground. When we found the bird or transmitter, we attempted to determine the cause of death based upon the condition of the carcass and other relevant signs, although we recognize that the activity of scavengers and other factors make assigning a source of mortality with certainty difficult (Bumann and Stauffer 2002). We classified mortality events as mammalian predation when woodcock carcasses were cached, typically with the heads missing or detached and sometimes with tooth marks on the transmitters. ...
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We estimated fall (10 Sep–8 Nov) survival rates, cause-specific mortality rates, and determined the magnitude and sources of mortality of 1,035 radio-marked American woodcock (Scolopax minor) in Michigan, Minnesota, and Wisconsin during 2001–2004. In all 3 states, we radio-marked woodcock on paired study areas; 1 of which was open to hunting and expected to receive moderate to high hunter use and the other of which was either closed to hunting (Michigan and Minnesota) or was relatively inaccessible to hunters (Wisconsin). We used Program MARK to estimate fall survival rates, to evaluate a set of candidate models to examine the effects of hunting and several covariates (sex, age, year, state) on survival, and to examine the relationship between survival rates and kill rates due to hunting. Hunting accounted for 70% of the 86 woodcock deaths in the hunted areas, followed by predation (20%) and various other sources of mortality (10%). Woodcock deaths that occurred in the non-hunted and lightly hunted areas (n = 50) were caused by predators (46%), hunting (32%), and various other sources (22%). Based on small-sample corrected Akaike's Information Criterion values, variation in fall survival of woodcock was best explained by treatment (i.e., hunted vs. non-hunted), year, and period (pre-hunting season intervals vs. hunting season intervals). The average fall survival estimate from our best model for woodcock in the non-hunted areas (0.893, 95% CI = 0.864–0.923) was greater than the average for the hunted areas (0.820, 95% CI = 0.786–0.854 [this estimate includes data from the lightly hunted area in Wisconsin]), and the average treatment effect (i.e., greater survival rates in non-hunted areas) was 0.074 (95% CI = 0.018–0.129). The kill rate due to hunting was 0.120 (95% CI = 0.090–0.151) when data were pooled among states and years. We detected a negative relationship between hunting kill rates and survival in our hunted areas, which suggests that hunting mortality was at least partially additive during fall. Our results illustrate the influence of hunting relative to other sources of mortality in Michigan, Minnesota, and Wisconsin, and indicate that managers may be able to influence fall survival rates by manipulating hunting regulations or access on public land. © 2013 The Wildlife Society.
... Mortality was assessed via evidence collected at the death site, field necropsy, or laboratory examination. Because of the lag-time in recovery of carcasses and the potential for scavengers to move carcasses or mask true mortality cause (Bumann and Stauffer 2002), I refer to "probable causes of mortality." I classified the probable cause of mortality as predation if evidence at the kill site contained dorsal guard hairs, feces, tracks, and pulled tendons, bite or puncture marks on carcass or radio-transmitter. ...
... Legal harvest removed 1 bird and the majority of mortalities were attributed to predation (n ¼ 34). Carcasses may have been subsequently scavenged after mortality, making it difficult to differentiate kills from scavenging events (e.g., Bumann and Stauffer 2002) and we found diagnostic sign at kill sites was unreliable for identifying predators of female sage-grouse and did not distinguish between avian or mammalian predation. We evaluated 18 candidate models to assess factors affecting bi-weekly survival rates ðŜÞ of female sage-grouse over an 8-month period (i.e., breeding season through autumn migration; Table 6). ...
Article
We examined demographic parameters and factors influencing nest survival of female greater sage-grouse (Centrocercus urophasianus) in northeastern California. Additionally, we used known-fate models in program MARK to examine bi-weekly survival rates of females over an 8-month period (Mar–Oct, 2007–2009). Nest survival rate, assuming a 38-day exposure period, was 41% and was positively associated with grass height ( = 0.03, SE = 0.02), but the 95% confidence interval overlapped 0 (95% CI = −0.007–0.767) and the effect of grass height on nest success was likely to be small. Grass height and visual obstruction was greater at nest sites than at random locations, suggesting females selected sites with structurally more closed habitat for nesting. Females that nested under vegetation other than sagebrush (Artemisia spp.) had increased nest survival probabilities, suggesting sage-grouse selection of nest sites is based on vegetation structure more than plant species. Sagebrush canopy cover was considerably lower in our study area (approx. 10% on random plots) compared with sagebrush cover described across the geographic range of sage-grouse (>15%) and sage-grouse use of non-sagebrush plants in our study suggests sagebrush nesting habitat is limited. The overall 8-month survival (breeding season through autumn migration) for female sage-grouse was 49% (SE = 0.06) with most deaths occurring in spring and autumn. Mortalities during spring coincided with nest initiation, incubation, and following hatch when successfully nesting females were tending to chicks. Mortalities in September coincided with dispersal and autumn migration. The survival estimate during the breeding season was greater among known failed nesters ( = 0.69) than females that nested successfully ( = 0.53), indicating female greater sage-grouse were exposed to greater mortality risk during incubation and brood-rearing periods. Greater mortality risk during the breeding season (i.e., nesting and brood-rearing) can have a major impact on greater sage-grouse demography. Conservation and management efforts should focus on enhancing female greater sage-grouse survival during the breeding and brood-rearing season. © 2014 The Wildlife Society.
... Unlike some transmitters, ours did not have mortality sensors and thus, we were not able to quickly determine if a transmitter was immobile. By only tracking 3 days per week, the likelihood of a scavenger tampering with a deceased bird or transmitter was increased in the interim, which could have biased our estimate in favor of mammalian scavenging (Bumann and Stauffer 2002). In areas where transmittered birds had dispersed into standing crops, we were unable to access the field until the crop was harvested and then, only briefly. ...
... Any time a mortality signal was detected, we recovered the radio-collar and determined the probable cause of death. We classified cause of death as predation, harvest, or unknown, and further classified predation as avian, mammal, or unknown based on field evidence (Bumann andStauffer 2002, Blomberg et al. 2013). Because we were unable to monitor ruffed grouse with high frequency (e.g. ...
Article
Understanding population dynamics and how species interact with their environment are important components for conservation and management. Ruffed grouse (Bonasa umbellus) are a widely distributed and common game bird in North America and are a considered an important economic and cultural icon in Maine. Although they are a well-studied species, there has been little research focused on ruffed grouse population dynamics and habitat relationships in Maine. My thesis aims to improve this knowledge gap by focusing on research related to survival and harvest of ruffed grouse, as well as male ruffed grouse resource selection at breeding display sites. Ruffed grouse are generally considered abundant in Maine, but there is a lack of states specific knowledge of their survival and harvest rates to inform harvest management. To address this component we estimated seasonal and annual survival rates, harvest rates, and documented cause-specific mortality of 248 radio-marked ruffed grouse at two study areas in central Maine from 2014 –2016. We used nest survival models implemented in Program MARK to evaluate sources of spatial, temporal, and individual variation that may affect survival and harvest. Our results showed survival was lowest during the month of October and during winter, and adult ruffed grouse had a higher survival probability than juveniles throughout the year (β -0.49 ± 0.15 SE). Harvest rates were greater in a state owned Wildlife Management Area, and were lower at our study area comprised of commercially-managed private forest (β=0.72 ± 0.38 SE). Pooled across all years and study areas, the ruffed grouse harvest rate was 0.16 (95% CI = 0.14-0.18). Our results are comparable to other range-wide studies, and suggest that ruffed grouse hunting regulations in Maine produce rates of harvest that are consistent with sustainable population management. Resource selection reflects behavioral choices that species make at different levels within their environment, but the fitness consequence of these choices are not always well understood. We evaluated habitat selection at breeding display sites, and the effects on breeding behavior, of male ruffed grouse in central Maine during April and May 2015–2016. We used resource selection functions (RSFs) that took the form of generalized linear models to compare habitat characteristics at used display locations (n=72) with those at available locations (n=144), and we further assessed how selected habitat features from the RSFs were associated with three drumming display characteristics; drumming rate, and wing beat rate. We used Akaike’s Information Criterion to assess model support and selection. We found that male ruffed grouse selected drumming locations with high total stem density (β=0.52, 95% CI= 0.22-0.82), as well as high conifer stem density within 5m from the display stage (β= 0.46, 95% CI= 0.17-0.75). However we did not find that these same variables were associated with drumming behaviors, suggesting no effect of habitat selection on breeding display behavior. Understanding habitat selection and the possible fitness consequences of those selection choices will allow managers to identify areas of critical habitat needed to further benefit the species.
... In addition to rodents, shrews (Soricidae), moles (Talpidae), and hedgehogs (Erinaceinae), as well as rabbits and hares (Lagomorpha), are also widespread in Europe, including the UK. Lagomorphs are occasional scavenging agents and can be observed, in rare cases, to feed on fresh animal carcasses and bone [91,133,134]. ...
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Animal scavenging by vertebrates can significantly alter human bodies and their deposition site. For instance, vertebrate animals can cause postmortem modification to a body, alter perimortem trauma, influence decomposition rates, disarticulate and scatter body parts or evidence, and affect the identification of the deceased. Animal scavenging is a relatively common occurrence in forensic investigations. Even so, studies on the subject are scattered and rare, with most focussing on geographical areas outside of Europe. For that reason, we intend to collate the literature to provide an account of forensically relevant vertebrate scavengers in Europe, their impacts on human remains, and their implications for forensic investigations. Here, we provide an overview of forensic aspects where the knowledge of animal scavenging is crucial, as well as an account of potential scavengers of human remains in Europe and their typical alterations to soft tissue and, in particular, to bones. In addition, we are the first to provide a guide for forensic practitioners to identify the presence of vertebrate scavenging and subsequently inform outdoor search strategies for affected human remains.
... We attempted to locate carcasses and identify the cause of mortality when VHF transmitters emitted a mortality pulse or PTT locations did not change for >2 days. Minimizing the response time to a mortality can help reduce the confounding effects scavengers may have on the carcass (Hagen et al. 2007) and we recognize that scavenging can complicate classifying causes of mortality (Bumann and Stauffer 2002). When mortalities occurred, we used evidence at the recovery site to classify the probable cause as avian, mammal, snake, collision, or unknown. ...
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Anthropogenic features increasingly affect ecological processes with increasing human demand for natural resources. Such effects also have the potential to vary depending on the sex and age of an individual because of inherent behavioral and life experience differences. For the lesser prairie-chicken (Tympanuchus pallidicinctus), studies on male survival are limited because most previous research has been focused on females. To better understand patterns of lesser prairie-chicken survival in habitat with varying levels of anthropogenic infrastructure associated with oil and natural gas development, we monitored survival of 178 radio-tagged male and female lesser prairie-chickens in eastern New Mexico, USA, from 2013 to 2015. We examined the relationships of shrub cover, proximity to and density of anthropogenic features (i.e., utility poles), displacement of natural vegetation by anthropogenic features (i.e., area of roads and well pads), and individual demographics (i.e., sex, age) with lesser prairie-chicken survival. Furthermore, we categorized the probable cause of mortality and examined its relationship with oil and gas development intensity (indexed by utility pole density) within 1,425 m of an individual's mortality site or final observed location. We predicted that survival would be lower for individuals exposed to greater levels of anthropogenic features, and that males and subadults would be more negatively affected than females and adults because of increased exposure to predators during the lekking season and naiveté. Relationships between survival and utility pole density, sex, and age were supported in our top-ranked models, whereas models including other anthropogenic and natural features (i.e., roads, well pads, shrub cover) received little support. We predicted a substantial decrease in adult and subadult male survival with increasing densities of utility poles. The relationship between survival and utility pole density for females was weaker and not as clearly supported as for males. We did not find a detectable difference in utility pole counts among probable mortality causes. Our findings highlight the importance of including male lesser prairie-chickens in research and conservation planning, and the negative effect that high densities of anthropogenic features can have on lesser prairie-chicken survival.
... range of other predators and scavengers (Bumann and Stauffer, 2002;Gomo et al., 2017). Examples include obligate and facultative avian scavengers worldwide including California condors (Gymnogyps californianus; Finkelstein et al., 2012;Finkelstein et al., 2010), Andean condors (Vultur gryphus; Wiemeyer et al., 2017), white-tailed sea eagles (Haliaeetus albicilla; Helander et al., 2009), golden eagles (Aquila chrysaetos; Ecke et al., 2017), and bald eagles (Haliaeetus leucocephalus; Warner et al., 2014;Cruz-Martinez, Grund and Redig, 2015). ...
Article
Wildlife and human health are at risk of lead exposure from spent hunting ammunition. Lead exposure persists for bald eagles due to bullet fragments in game animal gut piles and unretrieved carcasses, and is also a human health risk when wild game is procured using lead ammunition. Programs encouraging the voluntary use of nonlead ammunition have become a popular approach mitigating these effects. This study explored attitudes and experiences of United States Fish and Wildlife Service (USFWS) staff implementing an outreach program encouraging deer hunters to voluntary use nonlead ammunition on 54 National Wildlife Refuges (NWRs) in the Upper Midwest, U.S. to understand factors affecting program implementation. We conducted 29 semi-structured interviews of USFWS staff along with 60 responses from an open-ended survey question. Twelve themes emerged from the data and were grouped into three broad categories: (1) challenges of dealing with complex issues, (2) importance of messengers and messages, and (3) resistance from staff. Challenges of dealing with complex issues included administrative restraint and uncertainty, scope and scale of program, human health not an agency responsibility, contextual political influences, and public-private collaborations. Importance of messengers and messages included the importance of experience, and salience of human health risk. Finally, resistance from staff included skepticism of the science and motives behind the program, competing priorities for refuge staff, differing perceptions of regulatory and voluntary approaches, cost and availability of nonlead ammunition, and disregard by some about lead ammunition and human health risks. Staff identified numerous challenges implementing the program, many of which were external factors beyond the control of the participants. Understanding the factors affecting program implementation may help guide future efforts encouraging the voluntary use of nonlead ammunition.
... In terrestrial systems, novel resource availability can also lead to opportunistic trophic expansion. Snowshoe hares (Lepus americanus) have been observed scavenging on mammalian and avian prey [11] while eastern cottontail rabbits (Sylvilagus floridanus) have been recorded scavenging avian prey [12]. Functional groups may also blur during periods of resource hyperabundance. ...
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Tourism represents an important opportunity to provide sustainable funding for many ecosystems, including marine systems. Tourism that is reliant on aggregating predator species in a specific area using food provisioning raises questions about the long-term ecological impacts to the ecosystem at large? Here, using opportunistically collected video footage, we document that 61 different species of fish across 16 families are consuming tuna flesh at two separate shark dive tourism operations in the Republic of Fiji. Of these fish, we have resolved 55 to species level. Notably, 35 (63%) of the identified species we observed consuming tuna flesh were from ostensibly non-piscivorous fishes, including four Acanthuridae species, a group primarily recognized as browsers or grazers of algae and epibenthic detritus. Our results indicate that shark diving is having a direct impact on species other than sharks and that many species are facultatively expanding their trophic niches to accommodate the hyperabundance of resources provided by ecotourism.
... Many of the remains were degraded because of scavenging and decomposition; hence, cause of death could not be determined. The carcasses for which cause of death was determined may present a biased picture of mortality overall (Bumann and Stauffer, 2002;Faanes, 1987;Flint et al., 2010). Our experience underscores the difficult task of determining cause-specific mortality for a wide-ranging migratory species or whenever circumstances prevent prompt collections of fresh carcasses. ...
Article
The Aransas-Wood Buffalo Population (AWBP) of Whooping Cranes (Grus americana) has experienced a population growth rate of approximately 4% for multiple decades (Butler et al., 2014a; Miller et al., 1974). Population growth for long-lived species of birds is generally highly sensitive to variation in adult mortality rates (Sæther and Bakke, 2000). A population model for endangered Red-crowned Cranes (Grus japonensis) in Japan conforms to this pattern, where growth rate is most sensitive to adult mortality (Masatomi et al., 2007). Earlier analyses observed that the AWBP growth rate increased in the mid-1950s and that this increase was likely caused by reduced annual mortality rates, even while the population experienced slightly decreasing natality (Binkley and Miller, 1988; Miller et al., 1974). A more contemporary analysis of the AWBP determined that approximately 50% of variation in annual population growth could be explained by variation in annual mortality (Butler et al., 2014a). Therefore, as a vital rate, mortality is critical to the maintained growth of the AWBP.
... Many of the remains were degraded because of scavenging and decomposition; hence, cause of death could not be determined. The carcasses for which cause of death was determined may present a biased picture of mortality overall (Bumann and Stauffer, 2002;Faanes, 1987;Flint et al., 2010). Our experience underscores the difficult task of determining cause-specific mortality for a wide-ranging migratory species or whenever circumstances prevent prompt collections of fresh carcasses. ...
... If prairie-chickens were being killed at random locations across the landscape, ,12% of the carcasses should be found , 50 m from a fence in the most densely fenced areas (J-section pastures or 65 ha), and only ,6% would be found within that distance if fences were moderately dense (full-section pastures; i.e. 1 mile 2 or 259 ha). Even so, scavengers can move carcasses in excess of 50 m (Bumann & Stauffer 2002), and livestock trails along fence lines complicate the situation because we suspect that coyotes Canis latrans and other mammals make regular use of such trails, thereby encountering fence kills more often than they would in a homogenous landscape. For example, Bradley & Fagre (1988) reported that both coyotes and bobcats Felis rufa used fence lines and roads as travel lanes more often than expected by chance. ...
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Life-history studies of prairie grouse have focused on reproductive ecology, habitat use, movement patterns and survivorship, with only cursory or anecdotal references to mortality causes, or they have been of insufficient duration or scale to infer mortality patterns. Because mortality causes and patterns affect other life-history traits, their determination adds to our over- all understanding of grouse demographics. As part of a long-term study on lesser prairie-chicken Tympanuchus pallidicinctus natural history in Okla- homa and New Mexico, we recovered 322 carcasses of radio-tagged birds captured on leks. We were able to determine the cause of death for 260 of these birds. Predation by raptors accounted for the largest number of mor- talities (91), followed by collisions with fences (86), predation by mammals (76), collisions with power lines (4), and collisions with automobiles (3). Mortality causes differed considerably between study sites and between sexes, with all collisions more frequent in Oklahoma than in New Mexico, in females than in males, and in older than in young females. Although predation is a major cause of mortality, we argue that predator control may not be effective for grouse conservation. Moreover, in cases where top predators reduce mesopredator population densities, for example those of red foxes Vulpes vulpes, indiscriminate removal of predators may hasten the decline of grouse populations. Land managers striving to conserve prairie- chickens and other grouse species should attempt to reduce or eliminate collision mortality risks in addition to efforts to improve nesting or brood- rearing habitat. Collision risks should also be evaluated for potential re- lease sites of translocated or captive-reared grouse.
... E-mail: elena.bassi2812@gmail.com few decades, studies on scavenging and related topics aimed at identifying the main scavenger species (Travaini et al. 1998;Bumann and Stauffer 2002;Selva et al. 2003Selva et al. , 2005DeVault et al. 2011;Huijbers et al. 2013); assessing the rate of carrion consumption (Selva et al. 2003(Selva et al. , 2005; understanding the influence of weather on the ability to locate carcasses (Ruzicka and Conover 2011); assessing the effects of environmental variables on carcass use (Selva et al. 2005;Jennelle et al. 2009); and, finally, determining carcass persistence in the environment (Jennelle et al. 2009). ...
Article
We investigated the scavenging behavior of some vertebrate species inhabiting a mountainous area of Eastern Tuscany (Italy). Fieldwork was conducted by using camera traps from July 2010 to June 2013. The red fox (Vulpes vulpes) resulted to be the main scavenger species, followed by the wolf (Canis lupus), while the wild boar (Sus scrofa) resulted to be one of the less efficient scavengers, exploiting, in groups, only two carcasses. The wolf seemed to use carcasses mostly during the summer season, while no differences in red fox seasonal use of and visit to carcasses were detected. All the wild scavenger species showed a peak of activity between dusk and dawn, during both summer and winter, likely to minimize human disturbance. The red fox used carcasses whenever available, and in most cases it also was the first species arriving on a new carcass, with a very limited searching time. This paper represents the first Italian study on carrion use by Mediterranean vertebrate communities.
... Tourism to be harvest mortality. We recovered most carcasses within 1-2 days of death, but causes of mortality are tentative because we cannot discount the possible effects of scavenging of dead birds (Bumann andStauffer 2002, Larsen et al. 2008). If we were unable to determine cause of mortality because carcasses were too degraded when recovered, or if multiple signs of evidence were present, we considered the mortality event to be of unknown cause. ...
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Identifying relationships between habitat selection and population processes is important for habitat management and wildlife conservation. For prairie-obligate species, space use and demography in extant grasslands are influenced by habitat conditions caused by rangeland management practices associated with livestock production. Greater prairie-chickens (Tympanuchus cupido) are an indicator species for native tallgrass prairie ecosystems, but populations have declined in the Flint Hills ecoregion of eastern Kansas, USA because of intensification of rangeland management practices, including annual prescribed fire and high stocking densities. Patch-burn grazing is a rotational system that provides heterogeneous habitats and can improve productivity of grassland birds, but the effects of grazing systems on habitat use or survival of greater prairie-chickens are unknown. We used 3 types of survival analyses to investigate impacts of rangeland management on female greater prairie-chickens in the central Flint Hills during 2011–2013: Kaplan–Meier models and Cox proportional hazards to examine factors affecting annual survival rates, hazard functions to assess seasonal patterns of mortality, and Andersen–Gill models to explore the links between habitat selection and cause-specific mortality risk. Females captured at properties managed with patch-burn grazing had annual survival rates (0.61 ± 0.07 SE) that were 35% higher than females on properties managed with annual burning and intensive early cattle stocking (0.45 ± 0.06). Moreover, females that selected habitats associated with intensive management had increased mortality risk and were particularly vulnerable to avian predators, whereas females that selected habitats created by patch-burn grazing experienced lower overall mortality risk but were more vulnerable to mammalian predators. Overall mortality risk was significantly reduced under patch-burn grazing management, and widespread implementation of annual spring burning and intensive early stocking is likely depressing survival of greater prairie-chickens in the Flint Hills ecoregion. Our results join a growing body of evidence that patch-burn grazing can provide higher quality grassland habitats for native wildlife species than current rangeland management associated with intensive cattle production.
... Avian predators were the leading cause of predation, followed by mammalian predators and unidentified predators. We assigned mortality agents based on inspection of carcass remains and signs surrounding the relocated carcass or radiotransmitter, but Bumann and Stauffer (2002) concluded scavenging by mammalian predators altered field evidence of avian predation. Consequently, our results represent a minimum estimate of avian predation and a maximum estimate of mammalian predation. ...
... We posit that collisions with fences and other man-made structures are additive to mortality from predation, especially in dry years when recruitment is inadequate to offset low adult survivorship. Scavenging by mammals can occur within days at >50% of carcasses (Bumann and Stauffer 2002), and collisions with fences or powerlines may occur at a higher rate than is evident from necropsy. Bias in cause-specific mortality results can be due to lack of direct observation or misinterpretation of sign during necropsy. ...
... We posit that collisions with fences and other man-made structures are additive to mortality from predation, especially in dry years when recruitment is inadequate to offset low adult survivorship. Scavenging by mammals can occur within days at >50% of carcasses (Bumann and Stauffer 2002), and collisions with fences or powerlines may occur at a higher rate than is evident from necropsy. Bias in cause-specific mortality results can be due to lack of direct observation or misinterpretation of sign during necropsy. ...
... No call playbacks were used during telemetry. We tried to determine cause of death from carcasses and associated sign at a kill site as soon as possible after time of death, recognizing that scavengers can make it difficult to assess cause-specific mortality (Bumann and Stauffer 2002). Mortality events were classified as avian predation if feathers were plucked without evidence of chewing, roosting owls or raptors were found nearby, pellet or whitewash was found at the site, or no bite marks were found on the transmitter. ...
Article
In Canada and in British Columbia, the interior Western Screech-Owl (Megascops kennicottii macfarlanei) has been assessed as a species at risk primarily as a result of loss and degradation of low-elevation riparian habitat. Few data exist on population demographics of this subspecies. We analyzed annual survival of 19 radio-tagged adult owls from 2009 through 2013 using known-fate models. Time and sex dependence in annual survival rates were examined. The best approximating models suggested that female annual survival (28%) was lower than male survival (83%). Owl survival was lowest prior to incubation and during brood rearing, times when owls are most vocal. Mortality was attributed to avian predation and road mortality. Management practices to preserve habitat during the critical breeding period are encouraged in light of this research.
... Hunting removed 1 bird and the majority of mortalities were attributed to predation (n = 34). Because it is possible that carcasses might have been subsequently scavenged after mortality, making it difficult to differentiate kills from scavenging events (e.g., Bumann and Stauffer 2002), I considered the diagnostic sign at kill sites as unreliable for indentifying predators of female sage-grouse. Therefore, I did not distinguish between avian or mammalian predation. ...
... Causes of mortality were grouped into four categories based on the following criteria (Hagen et al. 2007, Wolfe et al. 2007). We discuss 'probable causes of mortality' because it is difficult to make unambiguous statements about causes of mortality if scavenging can occur (Bumann and Stauffer 2002). Cases where feathers, radios, or leg bands were chewed, had obvious tooth marks, and were clumped in a small area (~1 m²) were considered to be probable mammalian predation. ...
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Populations of Greater Prairie-Chickens (Tympanuchus cupido) have been declining because of loss and fragmentation of tallgrass prairie habitats, and management plans require contemporary demographic data. Our objectives were to determine whether maternal nutrition or predation were determinants of nesting success and female survival. We captured and radio-marked 43 females at four leks in natural, unfragmented prairie during a 4-year study. Reproductive potential was high because females laid large clutches (10.9 +/- 0.3 eggs, n = 24), renested following clutch loss (22.2%, n = 27 females), and had high egg viability (88.6 +/- 5.0% of eggs hatched; n = 7 nests), but reproductive traits were not correlated with female morphometrics (mass, or tarsus and keel lengths). Daily survival rate of nests was low (0.928, n = 34 nests) resulting in a predicted nest success rate of 7.4% for a 35-day exposure period. We used known fate models to estimate weekly survival from telemetry data for 40 females. Weekly survival was 0.970 and the extrapolated survival rate for the 6-month breeding season was 45.7%. Using time-sincemarking Cormack-Jolly-Seber models for live encounter data to control for transience, annual apparent survival was 0.277 +/- 0.081 SE for 55 marked females after initial capture, and 0.424 +/- 0.139 during subsequent intervals. Survival of females was 1.6 to 2.0 times higher during the nonbreeding season than the breeding season, presumably because females are susceptible to predation during incubation and broodrearing. Predation of nests and females may be the main demographic factors limiting population viability because predation, and not maternal nutrition, accounted for unexpectedly low nesting success and breeding season survival of Greater Prairie-Chickens in natural habitats. Future research should investigate rangeland practices that increase residual nesting cover or reduce predator impacts.
... Avian predators were the leading cause of predation, followed by mammalian predators, and unidentified predators. Mortality agents were determined by inspection of carcass remains and sign surrounding the relocated carcass or radio-collar, but Bumann and Stauffer (2002b) concluded scavenging by mammalian predators altered field evidence, thus our results represent a minimum estimate of avian predation and a maximum estimate of mammalian predation. In the core of ruffed grouse range northern goshawks (Accipiter gentilis) and great horned owls (Bubo virginianus) are considered the primary predators of ruffed grouse, but goshawks are rare in the Appalachian region (Bumann and Stauffer 2004); the primary predators in the Appalachians are the Cooper's hawk (Accipiter cooperii) and owls (Bumann and Stauffer 2004). ...
Article
Knowledge of the effects of hunting and environmental influences on survival of eastern wild turkeys (Meleagris gallopavo silvestris) is critical to managers setting fall and spring hunting seasons. Research has shown improper season frameworks can result in unsustainably high harvest rates of adult males, affect male age structure, and result in lower hunter satisfaction. Our objectives were to estimate survival rates of males, identify causes of mortality, and relate hunting and environmental influences to male turkey survival. We captured and radio‐tagged male wild turkeys in Virginia (n = 204) and West Virginia (n = 197), USA, during 2004–2007. We used staggered entry Kaplan‐Meier models to estimate survival and Cox Proportional Hazards Models to estimate effects of predictor variables on survival. Survival was estimated for 3 distinct periods of interest: annual, fall hunting (October–January), and spring hunting (April–May). The leading causes of mortalities (209 turkeys) were legal spring harvest (42%), predation (25%), and poaching (17%). Only 8 turkeys (4%) were taken during fall hunting seasons. Confidence intervals for annual survival of 2 year‐old and 3+ year‐old turkeys overlapped; therefore, we combined adult ages into a single category (2+). Adult (2+) annual survival was 0.63 (95% CI = 0.58–0.69) and the harvest rate was 25% (95% CI = 20–29%) for the combined states. Annual survival rates for adults (2+) were greater than in most other published studies, whereas adult (2+) spring harvest rates were lower. For juvenile males, annual survival was 0.74 (95% CI = 0.68–0.79) and spring harvest rate was 7% (95% CI = 3–11%). High juvenile and adult (2+) survival may have been related to low harvest rates. Adult turkeys (2+) had 46% greater risk of dying than one‐year‐old birds and were 3.7 times more likely to be harvested than juveniles. Age, a relative phenology index (RPI; spring green‐up), and white oak (Quercus alba) acorn production were included in the top models for annual survival, spring season survival, and spring harvest risk. Increasing RPI (more foliage) decreased mortality risk and greater white oak (Quercus alba) acorn abundance increased mortality risk. Across 4 regions in the 2 states, fall survival was high (0.90, 95% CI = 0.87–0.93). The impact of fall hunting on males in Virginia was low (5% harvest rate, 95% CI = 0–9%). Overall, spring harvest had the greatest effect on male survival, although those effects were moderated by the previous fall white oak crop and the onset of green‐up in the spring. Knowledge of the effects of hunting and environmental influences on survival of eastern wild turkeys (Meleagris gallopavo silvestris) is critical to managers setting fall and spring hunting seasons. Improper season frameworks can result in unsustainably high harvest rates of adult males, affect male age structure, and result in lower hunter satisfaction. Our objectives were to estimate survival rates of males, identify causes of mortality, and relate hunting and environmental influences to male turkey survival. Over 3 years (2004‐2007), we captured and radio‐tagged male wild turkeys in Virginia (n = 204) and West Virginia (n = 197), USA. Adult birds (2+) had 46% greater risk of dying than 1‐year‐old birds and were 3.7 times more likely to be harvested than juveniles. The impact of fall hunting on male turkey annual survival in Virginia was low.
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Understanding population dynamics is central to population management, particularly for game species that experience human harvest and non‐harvest mortality. Ruffed grouse (Bonasa umbellus) are a widely distributed and common game species in North America that have experienced population declines along their southern range margins, including portions of New England, primarily in response to forest succession and habitat loss. In the state of Maine, ruffed grouse are generally considered abundant, but there is a lack of state‐specific knowledge of ruffed grouse survival and harvest rates to inform harvest management. We estimated seasonal and annual survival rates, harvest rates, and documented cause‐specific mortality of 248 radio‐marked ruffed grouse at 2 study areas in central Maine from 2014 to 2016. We used Program MARK to evaluate sources of spatial, temporal, and individual variation that may affect ruffed grouse survival and harvest. Survival was lowest during October and during winter, and adult ruffed grouse had a higher survival probability than juveniles throughout the year with mean annual survival probabilities of 0.28 ± 0.01 (SE) and 0.13 ± 0.003, respectively. Harvest rates were greater in a state‐owned Wildlife Management Area and were lower within commercially managed private forest that was open to public hunting. Harvest results suggest harvest (H) was greatest at the beginning of the hunting season (Oct; Frye Mountain HOct = 0.14 ± 0.02; Stud Mill HOct = 0.07 ± 0.02), and was lower later in the season (Nov and Dec; Frye Mountain HNov‐Dec = 0.07 ± 0.02; Stud Mill HNov‐Dec = 0.03 ± 0.01). Pooled across all years and study areas, the ruffed grouse harvest rate was 0.16 (95% CI = 0.14–0.18). Our results are comparable to other range‐wide studies and suggest that current hunting regulations for ruffed grouse in Maine are consistent with sustainable population management. © 2018 The Wildlife Society.
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During 2 years of radiotelemetry research on chukars (Alectoris chukar) in western Utah, USA, we found 28% of retrieved radios (n = 78) in rubbish nests of woodrats (Neotoma spp.). Such movement and disturbance of carcasses and radios by woodrats and other species has implications for radiotelemetry studies. We evaluated spatio-temporal movement of 51 radiocollars attached to chukar carcasses in western Utah. Most (80%) carcasses were scavenged within one week and by the end of 3 weeks 25 (50%) had been retrieved from woodrat middens. Scavenging activity can both obscure important clues needed to identify causes of mortality and bias telemetry studies by delaying onset of mortality signals.
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Vertebrate scavengers are primary mechanisms for scatter and disarticulation of human remains in rural habitats. Because recovery of the body can be hampered by the degree of scatter due to scavengers, the methods used to search for body parts will influence how much is found and the length of time taken to recover the body. We compared the frequency of scavenging by vertebrates in two different habitats, a deciduous forest and a tall grass meadow, and measured the time taken to search for scattered remains within a designated search area using four methods. Freshly killed 23 kg pigs were placed in either a forest or tall grass meadow habitat, and scavenging by vertebrates was observed over a 5–6 day period. Subsequently, the link, line, zone, and spiral methods were used to search for remains within a 21 m2 search area. Three of 5 pigs in the forest and 4 of 5 pigs in the meadow habitat were scavenged by a variety of vertebrates. Mean time to search the designated area around each pig differed between the forest and the meadow, but not by search method. Mobility within each habitat likely explains the difference in search times, and also accounts for some of the variability between search methods.
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Greater Sage-Grouse (Centrocercus urophasianus) is a species of conservation concern and is highly susceptible to mortality from West Nile virus (WNV). Culex tarsalis, a mosquito species, is the suspected primary vector for transmitting WNV to sage-grouse. We captured, radio-tagged, and monitored female sage-grouse to estimate breeding season (April 15 to September 15) survival, 2016–2017. Deceased sage-grouse were tested for active WNV; live-captured and hunter-harvested sage-grouse were tested for WNV antibody titers. Additionally, we trapped mosquitoes with CO2-baited traps 4 nights per week (542 trap nights) to estimate WNV minimum infection rate (MIR). Eight sage-grouse mortalities occurred during the WNV seasons of 2016 and 2017, 5 had recoverable tissue, and 1 of 5 tested positive for WNV infection. Survival varied temporally with sage-grouse biological seasons, not WNV seasonality. Survival was 0.68 (95% CI: 0.56–0.78; n = 74) during the reproductive season (April 1 to September 15). Mammalian predators were the leading suspected cause of mortality (40%), followed by unknown cause (25%), avian predation (15%), unknown predation (15%), and WNV (5%). These results indicate WNV was not a significant driver of adult sage-grouse survival during this study. Three sage-grouse (1.9%; 95% CI: 0.5–5.9%) contained WNV antibodies. We captured 12,472 mosquitoes of which 3,933 (32%) were C. tarsalis. The estimated WNV MIR of C. tarsalis during 2016 and 2017 was 3.3 and 1.6, respectively. Our results suggest sage-grouse in South Dakota have limited exposure to WNV, and WNV was not a significant source of sage-grouse mortality in South Dakota during 2016 and 2017. Based on our finding that a majority of sage-grouse in South Dakota are susceptible to WNV infection, WNV could potentially have an impact on the population during an epizootic event; however, when WNV is at or near-endemic levels, it appears to have little impact on sage-grouse survival.
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The 2011 nuclear accident in Fukushima, Japan caused the evacuation of > 100,000 people and prompted studies on environmental impacts of radiological contamination. However, few researchers have explored how the human evacuation has affected ecosystem processes. Despite contamination, one common scavenger (wild boar, Sus scrofa) is 2–3× more abundant inside the Fukushima Exclusion Zone (FEZ). Shifts in abundance of some scavenger species can have cascading effects on ecosystems, so our objective was to investigate impacts of the evacuation and the resulting increase in wild boar on vertebrate scavenger communities. We deployed cameras at 300 carcasses in the FEZ and a nearby inhabited area, and quantified carcass fate, scavenger species, and detection/persistence times. We also tested effects of carcass size and habitat on scavenger community composition and efficiency by balancing trials across two carcass sizes and habitats in each zone. Overall scavenger richness and carcass removal rates (73%) were similar in the FEZ and inhabited area, but species-specific carcass removal rates and occurrence differed between zones. Wild boar removed substantially more carcasses inside the FEZ, with implications for nutrient and contaminant distribution. Our results suggest carcass size affects scavenging dynamics more than human activity or habitat, and abundance changes of common scavengers can influence carrion resource allocation.
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Declines in abundance of American woodcock (Scolopax minor; hereafter woodcock) have led to more restrictive hunting regulations imposed by the U.S. Fish and Wildlife Service, although there is little evidence to suggest that declines were related to hunting. To estimate winter survival and document hunting mortality rates, I radiotagged 160 female woodcock on a public hunting area in south central Louisiana. Woodcock were captured in fields at night from late November through December during 1994-96 and monitored at least daily. At least 37 woodcock died, primarily from avian predators. Day of capture and condition at date of capture were not predictive of survival. Survival rates were similar across ages and years except for lower survival of juvenile birds during 1993-94. The overall survival rate for the period 1 December to 15 February (77 days) was 72 ± 5%, which was the same or higher than reported elsewhere in winter. Hunting mortality varied from 1.6 to 12.2%, which seemed relatively low given the ample public hunting opportunity and a high winter-long fidelity to the study area.
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With a high carcass density (50 birds in 7.8 ha) scavenging rates were very rapid. Carcasses in exposed positions on land persisted for on average 1.5 days, those concealed by vegetation for 3.3 days and those exposed on water for 7.6 days. These differences are probably related to the identity and abundance of predators and scavengers and their foraging routes. High lead poisoning waterfowl mortality thus may occur unnoticed by hunters. -from Author
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We monitored 381 radio-marked ruffed grouse (Bonasa umbellus) on public and private wood-lands in central Wisconsin during 1982-88 to determine seasonal mortality rates due to predation and hunting. A total of 222 known mortalities were recorded: 159 from predation and 63 from hunting. Adult survival rates gradually decreased from 0.85 in summer to 0.57 in winter, then increased in spring to 0.73. Juvenile survival was also highest in summer (0.61), but remained relatively low through all seasons. Hunting mortality rates on public hunting areas were significantly (P < 0.005) higher than on private lands for both adults (0.73 vs. 0.13) and juveniles (0.56 vs. 0.09). In contrast, mortality (viz., predation) was similar during the nonhunting season on public and private lands for both adults (0.44 vs. 0.44) and juveniles (0.80 vs. 0.77, respectively), suggesting that hunting mortality was at least partially, if not completely, additive to natural mortality. Immigration from private lands sustained grouse numbers on public lands because overall population densities gradually increased from 5.8 to 7.8 drumming males per 100 ha during the 6-year study. We conclude that ruffed grouse numbers will be substantially reduced in areas with high hunting mortality and reduced immigration due to fragmented habitat.
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The use of salmon Salmo salar carrion by otters Lutra lutra and other scavengers along the River Dee in north-east Scotland was studied by radio-tagging and individual marking of fish carcasses. More carcasses were available on the Dee than on tributary streams used for spawning, indicating that salmon returned to the river after spawning and died there. The amount of salmon carrion available to terrestrial and avian scavengers along the Dee varied from 6.7 kg. km-1 on an upstream study area to 36 kg. km-1 downstream. Fish carcasses in the Dee were moved by spates up to 20 km but in streams used for spawning less than 1 km. Of 86 carcasses examined in 1990/91, 64 were available to terrestrial and avian scavengers on the bank or awash and of these 45 had been fed upon by otters and 16 by birds. In 1991/92, 23 of 30 carcasses were available to terrestrial and avian scavengers. All had been fed upon, 19 by otters, four by birds. Other carcasses, in shallow water, were not available to terrestrial and avian scavengers. Subsequent scavenging was mainly by otters and continued for up to three weeks after the carcasses were found. Heron Ardea cinerea, great black-backed gull Larus marinus and crow Corvus corone also scavenged salmon carcasses along the Dee. Great black-backed gulls were the most frequent scavengers, but heron (dominant to black-backed gull) was a major scavenger in 1990/91. Crows, subordinate to other scavengers, waited, often in pairs, upon dominant scavengers. There were more scavenging birds downstream and numbers did not change between years. Of 20 salmon carcasses placed in spawning areas eight were probably, two possibly, removed by otters. Otters continued to scavenge carcasses for up to a month. Scavenging by foxes Vulpes vulpes and birds followed the removal of fish carcasses from the water by otters. Radio transmitters were removed by otters and left lying alongside carcasses.
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This paper presents a review and critique of statistical null hypothesis testing in ecological studies in general, and wildlife studies in particular, and describes an alternative. Our review of Ecology and the journal of Wildlife Management found the use of null hypothesis testing to be pervasive. The estimated number of P-values appearing within articles of Ecology exceeded 8,000 in 1991 and has exceeded 3,000 in each year since 1984, whereas the estimated number of P-values in the Journal of Wildlife Management exceeded 8,000 in 1997 and has exceeded 3,000 in each year since 1991. We estimated that 47% (SE = 3.9%) of the P-values in the Journal of Wildlife;fe Management lacked estimates of means or effect sizes or even the sign of the difference in means or other parameters. We find that null hypothesis testing is uninformative when no estimates of means or effect size and their precision are given. Contrary to common dogma, tests of statistical null hypotheses have relatively little utility in science and are not a fundamental aspect of the scientific method. We recommend their use be reduced in favor of more informative approaches. Towards this objective, we describe a relatively new paradigm of data analysis based on Kullback-Leibler information. This paradigm is an extension of likelihood theory and, when used correctly, avoids many of the fundamental limitations and common misuses of null hypothesis testing. Information-theoretic methods focus on providing a strength of evidence for an a priori set of alternative hypotheses, rather than a statistical test of a null hypothesis. This paradigm allows the following types of evidence for the alternative hypotheses: the rank of each hypothesis, expressed as a model; an estimate of the formal likelihood of each model, given the data; a measure of precision that incorporates model selection uncertainty; and simple methods to allow the use of the set of alternative models in making formal inference. We provide an example of the information-theoretic approach using data on the effect of lead on survival in spectacled elder ducks (Somateria fischeri). Regardless of the analysis paradigm used, we strongly recommend inferences based on a priori considerations be clearly separated from those resulting from some form of data dredging.