Long-Term Study of Reproductive Performance in Golden Eagles in Relation to Food Supply in Boreal Sweden

The reproductive performance of the Golden Eagle (Aquila chrysaetos) was studied across 10-55 territories from 1980-2009, in relation to indices of their primary prey (grouse [Tetraonidae] species and mountain hare [Lepus timidus]) and cyclic vole (Myodes and Microtus) populations in northern Sweden's boreal forest. Reproductive performance was measured as the number of live nestlings >= 4 wk old (hereafter termed nestlings) per breeding attempt, the percentage of territories with nestlings, and as an annual population production index. Despite the large interannual variation in the reproductive performance of the Golden Eagle, autocorrelations did not reveal any short-term periodicity as had been predicted in the literature. Using multiple regression, we found that the index of annual population production and the percentage of territories with nestlings were significantly related to the concurrent indices of their primary prey populations. Further, the index of annual population production was also significantly related to the pooled abundance of voles (bank voles [Myodes glareolus] and field voles [Microtus agrestis]) in the previous autumn. In all, 28% of the total variation in the index of annual population production was explained by the prey population variables.