Bald Eagle home range size and core-use areas in an urbanizing landscape

Urbanization has contributed to the decline of many wildlife species through habitat loss. To examine how Bald Eagles (Haliaeetus leucocephalus) respond to urbanization we used dynamic Brownian bridge movement models to estimate home range size and core-use areas of 24 territorial Bald Eagles affixed with GPS/GSM transmitters during five different stages of the annual cycle. We then used a mixed-effects linear regression model to identify the land cover characteristics associated with home range size and core-use areas. We found that Bald Eagle home ranges and core-use areas varied in size and were often discontinuous. Home ranges and core-use areas tended to be larger during the pre-nesting and non-nesting stages and smaller during the nestling and post-fledge stages, with these differences being more pronounced in females. Home ranges and core-use areas were smaller in areas containing more water and lower canopy cover. Home ranges, but not core-use areas, were also smaller in areas containing higher amounts of herbaceous wetlands. Home range size was not strongly associated with impervious cover, a metric of human development intensity, but core-use area size increased with impervious cover. Eagle core-use areas did not contain more than an average of 39 % impervious cover, defined as low development intensity by the U.S. Geological Survey. In our study, home ranges covered areas with higher levels of impervious surface compared to core-use areas, demonstrating that while eagles will inhabit areas with moderate levels of development, they concentrate their use in areas with lower levels of development. These findings suggest that Bald Eagles can use urbanizing landscapes, but care should be taken to protect key nesting and foraging sites from high density development.