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Land types of segments with and without recorded bald eagle use on northern Chesapeake Bay, Maryland, 1990- 92.
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We studied the influence of shoreline perch trees and human development on bald eagle (Haliaeetus leucocephalus) distribution on the northern Chesapeake Bay. Bald eagle distributions may be determined by available suitable shoreline perch areas. Models based on human development and shoreline habitat variables may alleviate problems associated with...
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Citations
... Human disturbance and alterations of habitat, such as tree cutting, can influence nest distribution, since Bald Eagles tend to prefer nest sites in undeveloped areas (Fraser et al. 1985;Anthony and Isaacs 1989;Buehler et al. 1991;Gende et al. 1998) containing suitable perch trees for foraging and other activities (Chandler et al. 1995). Furthermore, nest productivity is also affected, hence higher nesting success in places where there is less human intrusion (Anthony and Isaacs 1989;Gende et al. 1998). ...
... The disturbance of eagles within foraging areas has received much attention by researchers over the past 30 years (Stalmaster and Newman 1978, Knight and Knight 1984, McGarigal et al. 1991, Brown and Stevens 1997. Frequent human activity associated with land development has led to the avoidance of hunting areas by foraging birds or presumptive habitat loss (Buehler et al. 1991a, Clark 1992, Chandler et al. 1995. Episodic human activities from the water (Knight and Knight 1984, McGarigal et al. 1991, Brown and Stevens 1997, air (Stalmaster and Kaiser 1997), or land Kaiser 1988, Grubb andKing 1991) flush eagles and disrupt hunting behavior. ...
We assessed diurnal activity patterns associated with communal roosts (n = 26) by tracking nonbreeding bald eagles (Haliaeetus leucocephalus; n = 58) within the upper Chesapeake Bay, USA, 2008–2013. We used daytime locations (n = 54,165) to map activity shadows (using home range analytics, 90% kernel) around communal roosts, to evaluate the spatial structure and to delineate diurnal activity centers. We overlaid a range (100–3,200 m) of buffers around the perimeter of each roost to estimate the benefits of management scenarios in extending protection to daytime activities. Activity shadows around roosts varied from 1.5 km2 to 116 km2 ( = 30.3 ± 5.48 [SE]), reflecting landscape context. Roosts with small (<10 km2) activity shadows tended to have simple shapes with roosts centrally located and positioned along primary shorelines. Roosts supporting large (>50 km2) activity shadows tended to have complex shapes with roosts not centrally located and set back from primary shorelines. Daytime locations were highly concentrated in areas near communal roosts (76% of locations within 2 km of roost perimeters). Diurnal activity centers (n = 38) included areas surrounding roosts and secondary activity centers that were primarily located along prominent shorelines. Communal roosts play a more significant and multi-faceted role in the eagle life cycle than we previously understood. Many of the roosts positioned along the shoreline provided resting places during the night and day, served as social gathering places during the day, and functioned as feeding locations. Evaluation of management buffers supports current management guidelines that recommend the establishment of 800-m buffers. Establishment of 800-m buffers within the study area would enclose 54% of all daytime locations, 66.7% of the area enclosed within activity centers associated with roosts, and 12.1% of the area enclosed in secondary activity centers.
... Examinations of step lengths and net square displacement plots further highlights that the species is mostly sedentary making use of short movements interspersed by longer movements, therefore likely relying on good perch spots. The importance of large trees for nesting and perching are also highlighted in the literature for Martial Eagles [25], and many other large birds of prey [84][85][86]. Datasets on actual tree composition in specific height classes (e.g. detailing the locations of very tall trees) may also provide better information on the species habitat preference rather than a single layer describing the density of trees over 5 m. ...
Understanding the ranging behaviours of species can be helpful in effective conservation planning. However, for many species that are rare, occur at low densities, or occupy challenging environments, this information is often lacking. The Martial Eagle (Polemaetus bellicosus) is a low density apex predator declining in both non-protected and protected areas in southern Africa, and little is known about its ranging behaviour. We use GPS tags fitted to Martial Eagles (n = 8) in Kruger National Park (KNP), South Africa to describe their ranging behaviour and habitat preference. This represents the first time that such movements have been quantified in adult Martial Eagles. Territorial eagles (n = 6) held home ranges averaging ca. 108 km². Home range estimates were similar to expectations based on inter-nest distances, and these large home range sizes could constrain the carrying capacity of even the largest conservation areas. Two tagged individuals classed as adults on plumage apparently did not hold a territory, and accordingly ranged more widely (ca. 44,000 km²), and beyond KNP boundaries as floaters. Another two territorial individuals abandoned their territories and joined the ‘floater’ population, and so ranged widely after leaving their territories. These unexpected movements after territory abandonment could indicate underlying environmental degradation. Relatively high mortality of these wide-ranging ‘floaters’ due to anthropogenic causes (three of four) raises further concerns for the species’ persistence. Habitat preference models suggested Martial Eagles used areas preferentially that were closer to rivers, had higher tree cover, and were classed as dense bush rather than open bush or grassland. These results can be used by conservation managers to help guide actions to preserve breeding Martial Eagles at an appropriate spatial scale.
... Hence, most African fish eagles are more likely to be distributed in areas offering the highest density of prey. African fish eagles are a species of aquatic ecotone habitat, with live fish accounting for the bulk of its diet (Chandler et al., 1995). However, non-fish prey has also been reported as forming a considerable proportion of African fish eagle diet probably representing both opportunistic hunting, especially when conditions for fishing are poor, and also the killing of other predators robbing African fish eagle nests (Stewart et al., 1997). ...
... Hence, most African fish eagles are more likely to be distributed in areas offering the highest density of prey. African fish eagles are a species of aquatic ecotone habitat, with live fish accounting for the bulk of its diet (Chandler et al., 1995). However, non-fish prey has also been reported as forming a considerable proportion of African fish eagle diet probably representing both opportunistic hunting, especially when conditions for fishing are poor, and also the killing of other predators robbing African fish eagle nests (Stewart et al., 1997). ...
African fish eagles (Haliaeetus vocifer) are important birds of prey and indicator of ecosystem integrity in aquatic environments. We assessed the population abundance and spatial distribution of African fish eagles along three major rivers in Gonarezhou National Park, Zimbabwe. Data were collected using walked transect surveys along Mwenezi, Runde and Save rivers in Gonarezhou between March and April 2011. A total of 54 African fish eagles were recorded with an average density of 0.62 individuals per km. African fish eagles were mostly distributed in areas with large water pools along Gonarezhou’s three major rivers. The results suggest that large pools along perennial rivers are important in the distribution and density of African fish eagles in Gonarezhou. Future studies should aim at establishing the long-term population trends of birds of prey in Gonarezhou.
... 'detection effect'; Lima 1994). Vigilance and the general capacity to respond rapidly to stimuli are important for visually oriented predators such as diurnal raptors (Andersson 1981, Bohall & Collopy 1984, Chandler et al. 1995 ). Tree height can be a predictor of perch use by raptors, particularly in level terrain (Stalmaster & Newman 1979 ). ...
As part of a program to recover the peregrine falcon Falco peregrinus in the southeastern U.S. we recorded perching behaviour with the objective of characterizing perches used in the reintroduction area. We used a site-attribute design and logistic regression to compare characteristics between used and non-used perches. Peregrines used pines Pinus spp. exclusively, while pines comprised 78% of available trees. Perches were larger than non-used trees (diameter at breast height in cm (in x¯ ± SD); 29.2 ± 15.7 and 23.9 ± 10.3), in more advanced stages of decay (2.5 ± 1.5 and 1.5 ± 1.1 (index)), and usually dominant in crown class (1.5 ± 0.6 and 1.7 ± 0.5 (index)). Perches were always on cliff plateaus and tended to be situated in sites with a less even canopy (0.5 ± 0.3 and 0.7 ± 0.2 (index)) and fewer deciduous stems (1.8 ± 3.4 and 2.3 ± 2.3 (stem density)) than non-used trees. These attributes depict selection of perches that provide unobstructed flight paths, good visibility, and a capacity to detect and respond rapidly to stimuli.
... Addition of perches, even if only a few metres high (Fig. 2), can therefore substantially improve habitat suitability for some predator species in areas where perches are rare or lacking (e.g. Widén 1994;Chandler et al. 1995;Malan & Crowe 1997;Sonerud 1997;Sheffield et al. 2001). ...
Summary • Predators hunting by sight often search for prey from elevated perches or hovering positions above the prey habitat. Theory suggests that prey visibility depends strongly on predator perch height and distance, but their quantitative effects have not been experimentally tested in natural habitats. • We estimate for the first time how prey visibility depends on predator perch height, distance and vegetation height in an open natural habitat, based on visibility measurements of two targets: a mounted bird and a graduated plate, from five perch heights (0·2–8 m) and six distances (5–120 m). • For both targets, their proportion visible increases strongly with observer perch height and proximity. From the lowest perch, visibility of the target bird declines to • Models of predator search suggest that hunting success and predation rate depend strongly on the prey detection rate, which is expected to decline with distance r approximately as r−d. However, d, the distance decay parameter, has not previously been empirically estimated in natural predator habitats. For distance – prey visibility relationships similar to those observed here, we find a realistic estimate of d to be 2·1–2·4. • The results demonstrate the crucial role of relative perch and vegetation height for prey visibility, which is of relevance for habitat management. The strong increase of prey visibility with predator search height suggests that removal of predator perches can improve the survival of endangered prey populations in open habitats. Conversely, perch preservation or addition can improve habitat suitability for some predator species where perches are rare or lacking.
... The distribution of perch trees and human disturbance had a greater influence on the distribution of wintering eagles on the mid-Columbia than did food abundance (Eisner 1991). An examination of perch tree use and human development around Chesapeake Bay found eagles used perches in shoreline segments that had a larger percentage of forest cover, more large trees with stout horizontal limbs, and trees that were closer to the water, than segments of unused shoreline (Chandler et al. 1995). ...
... The authors concluded that shoreline development causes an irretrievable loss of eagle habitat. Chandler et al. (1995) found the best predictors of eagle use on Chesapeake Bay shorelines were development density and distance from water to the nearest tree. ...
... Most recent work in urban areas has focused on birds and mammals. The technique has been used to study bald eagle (Haliaeetus leucocephalus) use of open space in the Chesapeake Bay watershed (Chandler et al. 1995), and movements and home range of Cooper's hawks (Accipiter cooperii) during the breeding season in Tucson, Arizona (Mannan and Boal 2000). Raccoon population density and survival in relation to rabies were studied in Rock Creek Park, in the Washington, D.C. metropolitan area (Riley et al. 1998) as was survival and movements of translocated raccoons in north central Illinois (Mosillo et al. 1999). ...
Wildlife biologists working in the urban environment, and students planning to become urban biologists, should be knowledgeable of techniques in wildlife field research and monitoring, habitat restoration and management, habitat conservation planning, human dimensions research and management, and management of nuisance situations and problem animals, relative to the metropolitan environment. Civilization has become increasingly urban, and the process of urbanization continues worldwide. Urban wildlife biologists must work with the cumulative effect of human population growth, urbanization, and land use changes on the natural landscape and with the human dimensions impacts of societal priorities and programs.
Plant and animal communities are modified by urbanization. A pattern of change in such communities is emerging. Urbanization results in a loss of native and increase of exotic species with lower overall species richness compared with predevelopment conditions. Many animal communities in urban areas, however, show higher biomass and density because of mass occurrence of a few highly successful species that tend to be generalists with broad ecological tolerance as opposed to specialists with more narrow tolerance. For effective management, biologists must understand the factors that shape urban plant and animal communities.
Urban biologists generally use field research and monitoring techniques that nonurban biologists use. For birds, belt transects, point counts, and territorial mapping of breeding pairs are used to study diversity, distribution, density, and abundance. Live trapping is frequently used for studying these factors in urban mammals. Radiotelemetry is used for examining habitat use, home range size, survival, and movement patterns of a wide variety of species. Habitat gradients can be used to study impact of urbanization and artificial nests to study nest predation in the urban environment. Other techniques include use of playback recordings of owl calls to study habitat use and mail questionnaire surveys to ascertain presence of coyotes and bobcats in metropolitan areas.
Techniques that have been used historically to restore and manage wildlife generally include: passage of laws and regulations, establishment of refuges, control of predators, reintroduction, feeding, erection of nesting structures, and habitat restoration and management. All have application to the urban environment. With regard to habitat restoration and management, techniques generally include: no active management, advancing succession, setting back succession, managing edges, restoring and managing streams and wetlands, and managing human activity.
Habitat conservation planning techniques should strive to maintain regional species diversity and meet human needs and desires. The overall strategy is to integrate conservation and development planning for long-term maintenance of environmental quality. Based on island biogeography theory, urban biologists identify core areas of high conservation value, surrounded by multiple-use buffer zones, and interconnected with habitat corridors. Biologists must work with planners and landscape architects in implementing a conservation strategy. Cluster-type development often is helpful in this regard as it offers greater flexibility than does traditional-type development for maintaining some natural land features and habitats.
Both qualitative and quantitative techniques are used in human dimensions work to gain understanding of public knowledge and attitudes regarding wildlife. Qualitative methods include in-depth interviews, facilitated small-group processes, direct observation, and analysis of written documents. Quantitative methods make use of face-to-face interviews, telephone interviews, mail surveys, behavioral observations, content analysis (making inferences from text), and secondary data analysis (using pre-existing data). Citizen task forces, which involve stakeholders in the management decision-making process, are used to resolve conflicts in some situations.
Urban biologists must be knowledgeable of techniques for managing nuisance situations and problem animals. One-way doors, which allow animals in a house or other building to leave but not to reenter, may be used for many situations. Scaring tactics are often used to reduce bird use of an area. Tape-recorded alarm and distress calls of birds can be played through loud speakers at roost sites, and “shell crackers” and automatic gas exploders also can be effective. Generally, it is better to integrate a combination of techniques into a scaring program, as no single technique is effective when used alone. Problems with nuisance wildlife usually are because of overabundance of one or more habitat components—food, cover, water, or space. Biologists attempt to manipulate these components to reduce or eliminate the nuisance situation or problem animal.
... Simultaneous with increasing shoreland development has been an increasing awareness of the ecological importance of these areas. Riparian and littoral areas of inland lakes are critical habitat for wildlife (Landin 1979, Odum 1979, Racey and Euler 1982, Fowler and Howe 1987, Chandler et al. 1995, Engel and Pederson 1998, Radomski and Goeman 2001, Woodford and Meyer 2002, Lindsay et al. 2002) and protect water quality (Bannerman et al. 1993, Engel and Pederson 1998, Kent 1998 ). Additionally, naturally vegetated shorelines have a strong aesthetic appeal (Korth 1994, Shifferd 1998). ...
Development of lakeshores has occurred at unprecedented levels in recent decades. Changes in the shoreland ecosystem concomitant
with this development have been little studied. In this study, we compared the structural and floristic characteristics of
vegetation at 97 developed and 85 undeveloped (reference) shoreland sites in northern Wisconsin, USA. Quantitative comparisons
of vegetation structural characteristics (percent cover of canopy, subcanopy, and understory vegetation layers; percent of
shoreline overhung by trees and shrubs; and amount of coarse woody debris) showed significantly greater complexity and cover
at undeveloped versus developed sites. We classified plant communities and described plant species composition along three
belt transects parallel to shore (upland, shoreline, and shallow water) using ordination techniques to describe the differences
between developed and undeveloped sites, as well as among undeveloped sites. The mean number of plant species and the percent
of native species were both greater at undeveloped than at developed sites along all three transects. Undeveloped upland sites
could be grouped by plant species composition into three types: Northern Wet Forest (bog species), Northern Mesic Forest,
and Northern Xeric Forest. Undeveloped shoreline vegetation was also clustered into three categories: bog species, upland
species with an abrupt transition to aquatic species, and wet meadow species. Soil characteristics further distinguished the
upland and shoreline categories. No distinct vegetation categories emerged in the shallow water ordination. We recommend that
appropriate species for shoreland restoration efforts be selected based on the native plant communities present at the undeveloped
sites, their relative location along an upland to shallow water gradient, and, in some cases, soil characteristics.
