Ecological and environmental correlates of territory occupancy and breeding performance of migratory Golden Eagles Aquila chrysaetos in interior Alaska CAROL L. MCINTYRE* & JOSHUA H. SCHMIDT U.S. National Park Service, 4175 Geist Road, Fairbanks, AK 99709, USA Understanding relationships between environmental conditions and reproductive param- eters is important when interpreting variation in animal population size. The northwest- ern North American population of Golden Eagles Aquila chrysaetos canadensis initiates courtship and nesting in early spring when prey diversity is low and weather conditions are severe. Snowshoe Hare Lepus americanus and Willow Ptarmigan Lagopus lagopus , the primary prey of Golden Eagles early in their nesting season in interior Alaska, both exhi- bit cyclical fluctuations in abundance, providing the opportunity to investigate such rela- tionships. We used Bayesian hierarchical models to explore variation in territory occupancy, nesting rates, nesting success and productivity of Golden Eagles from 1988 to 2010 in Denali National Park and Preserve, Alaska, in relation to annual and site- specific parameters including prey abundance, weather conditions, elevation and human activity. We also investigated the long-term fluctuations of breeding performance over the course of the study. The abundance of Hares influenced both the number of Eagles that laid eggs and the number of Eagles that produced fledglings. The conditions on the breeding ground did not explain observed declines in nesting rates and fledgling produc- tion, suggesting that other factors such as change in the age structure of the population, increased intraspecific competition or deterioration of migration and wintering habitat are driving the long-term trends of these parameters. Keywords: breeding biology, long-term study, population monitoring, prey abundance, weather. Prey abundance is one of the primary factors driv- ing the reproductive success of raptors (Newton 1979, Krebs et al. 2001), but weather and human activities can also affect reproduction (Steenhof et al. 1997, Steidl & Anthony 2000). Variation in breeding performance related to prey cycles, weather and human disturbance may obscure trends in the reproduction of long-lived species, and long-term studies are necessary to assess ade- quately their population parameters. The data required for assessments of long-lived predator and prey species of interest must be collected over dec- ades (Arthur & Prugh 2010), and such datasets are rare. However, when collected and analysed in a continuous and rigorous manner, they provide unique opportunities to investigate complex preda- tor–prey relationships, identify patterns, and increase knowledge of species and their environ- mental associations (Newton 1998, Sundell et al. 2004, Anthony et al. 2008). Raptors exhibiting specialized diets show strong responses to changes in the abundance of their primary prey (Newton 1998) and have few alternative food sources when their primary prey decline in abundance. Raptors that prey heavily on species that exhibit cyclical patterns in abundance also show strong responses to changes in prey abundance, with reproduction increasing when prey abundance is high and decreasing when it is low (Doyle & Smith 1994, Steenhof et al. 1997, McIntyre & Adams 1999, Whitfield et al. 2009). Snowshoe Hare Lepus americanus and Willow Ptarmigan Lagopus lagopus exhibit large-amplitude population cycles across North America (Boutin et al. 1995, Hodges et al. 2001, Krebs et al. 2001, Martin et al. 2001). Changes in the abundance of *Corresponding author. Email: carol_mcintyre@nps.gov No claim to original US Government works Ibis ª 2011 British Ornithologists’ Union Ibis (2012), 154, 124–135