(2007) reported a roughly 700% increase in the nesting population from 1981 to 2005, a population growth rate of 9% annually. In Washington State, resident bald eagle numbers have increased dramatically. 2011), and possibly other prey resources. 2010), terrestrial mammals ( Newsome et al. Bald eagles are top predators capable of depleting populations of seabirds ( Parrish et al. Though this recovery is clearly a conservation success story, growing numbers of bald eagles present challenges to natural resource management because bald eagles are large, mobile, endothermic animals with high metabolic demands ( Stalmaster and Gessaman 1984) and diverse, opportunistic dietary habits (e.g., Stinson et al. This recovery follows a broad range of protective actions, and led to bald eagles being removed from the U.S. Future climate-driven declines in winter food availability, coupled with a growing bald eagle population, may force eagles to seek alternate prey in the Puget Sound area or in more remote ecosystems.īald eagle ( Haliaeetus leucocephalus) populations, once decimated by stressors such as hunting, prey declines, predator control, habitat loss, and chemicals such as DDT, have largely recovered in the continental United States ( USFWS 2007). That estimate is likely conservative, as it does not account for decreased availability of carcasses due to anticipated increases in winter stream flow. However, the warming climate caused salmon carcasses to decompose more rapidly, resulting in 11% to 14% less annual carcass biomass available to eagles in the 2050s. Bald eagle bioenergetics were insensitive to climate change: despite warmer winters in the 2050s, particularly near the Nisqually River, bald eagle food requirements declined only slightly (<1%). Climate data were used to drive bald eagle bioenergetics models from December to February for each river, year, and decade. We applied a regional downscaling method to two global climate change models to obtain hourly temperature, precipitation, wind, and longwave radiation estimates at the mouths of three Puget Sound tributaries (the Skagit, Hamma Hamma, and Nisqually rivers) in two decades, the 1970s and the 2050s. We used modeling techniques to examine how anticipated climate changes will affect energetic demands of overwintering bald eagles. Thousands of bald eagles overwinter near Puget Sound, primarily to feed on chum salmon ( Oncorhynchus keta) carcasses. Bald eagles ( Haliaeetus leucocephalus) are recovering from severe population declines, and are exerting pressure on food resources in some areas.
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