Seasonal Variation in Space Use by Nonbreeding Bald Eagles Within the Upper Chesapeake Bay

Watts, Bryan D.; Mojica, Elizabeth K.; Paxton, B J

doi:10.3356/jrr-13-61.1

Cited by 9 publications

(6 citation statements)

References 24 publications

(27 reference statements)

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“…The heightened winter-time dependency on AFSs is further supported by studies in Greenland [49], the Austrian and Bavarian Alps [23,83], Alaska [32], North Finland [84] and North Wales [76], that have all noted increases in the number of ravens present at AFSs in winter. Similar observations exist for other species that exploit anthropogenic resources to a larger extent during the harsher winter months such as Kea Nestor notabilis [85], Bald Eagles Haliaeetus leucocephalus [86,87] and White storks Ciconia ciconia [88]. Given the seasonality in AFS dependency exhibited by ravens, targeted wintertime food closures could provide an effective non-lethal management strategy to control population growth.…”

Section: Seasonal Differencessupporting

confidence: 66%

The spatial and temporal exploitation of anthropogenic food sources by common ravens (Corvus corax) in the Alps

Jain

Bugnyar

Cunningham³

et al. 2022

Mov Ecol

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Background Anthropogenic food sources (AFSs) are widespread in human-transformed landscapes and the current scale at which they occur drives ecological change at the individual, population, and community levels. AFSs are exploited extensively by common ravens, Corvus corax. Understanding how raven populations use AFSs can provide insight into their ecological responses to AFSs. Methods We equipped 81 ravens in the Austrian Alps with GPS-transmitters over a period of 2.75 years. Using these tracking data, we investigated how cohort differences (i.e., age, sex, and origin) and seasonal changes influence raven movement patterns (i.e., occurrence distribution and maximum daily displacement) and AFS-use (i.e., number of AFSs visited and probability of being present at any AFS) at 45 extensively exploited sites. Results We found that proxies for experience and dominance, inferred by age (i.e., juvenile versus adult) and origin (i.e., wild-caught versus captive-bred-released) cohorts, influenced movement patterns and the number of AFSs visited. However, all individuals were equally likely to be present at AFSs, highlighting the importance of AFSs for non-breeders in the study population. Seasonal changes in environmental conditions that affect energetic demands, the availability of natural and anthropogenic food, and foraging competition, influenced individuals’ occurrence distributions and AFS-use. We found that under harsher conditions in autumn and winter, individuals ranged wider and depended on AFSs to a larger degree. However, contrary to expectation, they were less likely to be present at AFSs in these seasons compared to spring and summer, suggesting a trade-off between time spent moving and exploiting resources. We attribute the small ranging movements exhibited by non-breeders in spring and summer to the presence of highly territorial and socially dominant breeders. As breeders mostly stay and forage within their territories during these seasons, competition at AFSs decrease, thereby increasing the likelihood of individuals being present at any AFS. Conclusions We emphasize that movement and AFS-use differ according to cohort differences and the seasonality of the environment. Our results highlight that predictable AFSs affect foraging strategies among non-breeding ravens. The extent of AFS-exploitation among non-breeding ravens in our study emphasize the potential of AFSs in shaping raven movement and resource-use.

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Section: Seasonal Differencessupporting

confidence: 66%

The spatial and temporal exploitation of anthropogenic food sources by common ravens (Corvus corax) in the Alps

Jain

Bugnyar

Cunningham³

et al. 2022

Mov Ecol

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“…Utilization distributions allow for the mapping of the intensity of use within a defined area [ 32 ]. Following Watts et al [ 33 , 34 ] we used Brownian bridge movement modeling to develop utilization distributions for each individual eagle using locations ( n = 245,865) collected between May 2010 and January 2016. We used the R package ‘move’ [ 31 ] to produce UD surfaces using the dynamic Brownian bridge movement model (dBBMM) [ 35 ].…”

Section: Methodsmentioning

confidence: 99%

“…The first category represents the minimum area to achieve 10% of the total utilization, the second category reflects the minimum area to achieve the next 10% of the total utilization, etc. This presentation thus allows for visualization of the relationship between the intensity of use and area [ 34 ].…”

Section: Methodsmentioning

confidence: 99%

To migrate, stay put, or wander? Varied movement strategies in bald eagles (Haliaeetus leucocephalus)

Wheat

Lewis

Wang³

et al. 2017

Mov Ecol

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BackgroundQuantifying individual variability in movement behavior is critical to understanding population-level patterns in animals. Here, we explore intraspecific variation in movement strategies of bald eagles (Haliaeetus leucocephalus) in the north Pacific, where there is high spatiotemporal resource variability. We tracked 28 bald eagles (five immature, 23 adult) using GPS transmitters between May 2010 and January 2016.ResultsWe found evidence of four movement strategies among bald eagles in southeastern Alaska and western Canada: breeding individuals that were largely sedentary and remained near nest sites year-round, non-breeding migratory individuals that made regular seasonal travel between northern summer and southern winter ranges, non-breeding localized individuals that displayed fidelity to foraging sites, and non-breeding nomadic individuals with irregular movement. On average, males traveled farther per day than females. Most nomadic individuals were immature, and all residential individuals (i.e. breeders and localized birds) were adults.ConclusionsAlternative movement strategies among north Pacific eagles are likely associated with the age and sex class, as well as breeding status, of an individual. Intraspecific variation in movement strategies within the population results in different space use patterns among contingents, which has important implications for conservation and management.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-017-0102-4) contains supplementary material, which is available to authorized users.

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“…Nonbreeding eagles within the upper Chesapeake Bay study area vary their space use according to season (Watts et al ). Within the available network of roost sites, roosts used exclusively during winter or summer are referred to as seasonal and roosts used consistently throughout the year are referred to as year‐round (Buehler et al , Watts and Mojica ).…”

Section: Methodsmentioning

confidence: 99%

“…Remaining portions of the study area are primarily rural, with forest lands interspersed with agriculture. These areas support an extensive network of communal roosts (Buehler et al , Watts and Mojica ) and many significant foraging areas (Watts et al ,).…”

Section: Study Areamentioning

confidence: 99%

Mapping bald eagle activity shadows around communal roosts

Watts

Turrin

2017

J Wildl Manag

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We assessed diurnal activity patterns associated with communal roosts (n ¼ 26) by tracking nonbreeding bald eagles (Haliaeetus leucocephalus; n ¼ 58) within the upper Chesapeake Bay, USA, 2008-2013. We used daytime locations (n ¼ 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 km 2 to 116 km 2 ( x ¼ 30.3 AE 5.48 [SE]), reflecting landscape context. Roosts with small (<10 km 2 ) activity shadows tended to have simple shapes with roosts centrally located and positioned along primary shorelines. Roosts supporting large (>50 km 2 ) 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 ¼ 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. Ó 2017 The Wildlife Society.

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Seasonal Variation in Space Use by Nonbreeding Bald Eagles Within the Upper Chesapeake Bay

Abstract: BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Cited by 9 publications

References 24 publications

The spatial and temporal exploitation of anthropogenic food sources by common ravens (Corvus corax) in the Alps

The spatial and temporal exploitation of anthropogenic food sources by common ravens (Corvus corax) in the Alps

To migrate, stay put, or wander? Varied movement strategies in bald eagles (Haliaeetus leucocephalus)

Mapping bald eagle activity shadows around communal roosts

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