REPRODUCTIVE SUCCESS OF BALD EAGLES IN INTERIOR ALASKA

We compared productivity and nesting success of 2 adjacent populations of bald eagles (Haliaeetus leucocephalus) near the northern limits of their range in interior Alaska during 1989-94. Productivity ((x) over bar x +/- SE young fledged/occupied territory) and nesting success di ffered between populations; pairs in the Gulkana River basin had highe r productivity (0.86 +/- 0.05, n = 274) and nesting success (59%) than those in the Copper River basin (0.71 +/- 0.04, 48%, n = 471; P < 0.0 2). Productivity varied both annually and spatially within each basin (P < 0.001). However, brood sizes of successful nests were identical f or both basins (1.48 +/- 0.03), suggesting that variability in product ivity resulted largely from differences in nesting success. Patterns o f variability in reproductive success within a territory also were sim ilar for both populations. Pairs that were successful one year hedged more offspring, were more Likely to be successful, were more likely to reoccupy the same territory and were less likely to change nest locat ions the following year compared to pairs that were unsuccessful the p recious year (P < 0.025 for all comparisons). Most nesting failure (92 %) occurred during incubation when weather conditions tend to be most severe. However, reproductive success was not negatively correlated wi th severity of spring weather (temp or rainfall) or strongly correlate d with prey abundance during brood rearing. We hypothesize that annual and spatial variability in reproductive success of these northern bal d eagle populations may be associated with variation in prey availabil ity, especially before and during incubation.