Beginning in the late 1980s, Florida Bay underwent dramatic ecological changes due to altered freshwater inflows from the Everglades. At the same time, the local Bald Eagle population began to decline, a trend that has continued ever since. We documented diet and provisioning rates of eagles to examine the hypothesis that food is a limiting factor to their success. We monitored 4 nests with video cameras in the 2009/2010 and 2010/2011 breeding seasons. We recorded a total of 546 prey deliveries, with 93% determined to class and 46% determined to family. Fish comprised 86% of all deliveries, birds made up 7%, and up 7% were undeterminable items. The mean daily provisioning rates for all nest sites combined were 1.75 deliveries/young/day and 2.64 deliveries/day. These rates significantly declined throughout the breeding season. They are strikingly smaller than those reported for stable Bald Eagle populations and comparable to the rates of another struggling population. The total biomass of prey deliveries/young/day also declined throughout the breeding season. Deliveries were mostly frequently made to the nest during the daily period 3–5 hours after sunrise and then again at a less frequent rate 9–12 hours after sunrise and did not vary between nests or change throughout the breeding season. These results suggest that the Bald Eagle population in Florida Bay is experiencing inadequate prey availability, which may be contributing to their decline.
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1 June 2016
Provisioning Rates Suggest Food Limitation for Breeding Bald Eagles in their Southernmost Range
Matthew R. Hanson,
John D. Baldwin
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Southeastern Naturalist
Vol. 15 • No. 2
June 2016
Vol. 15 • No. 2
June 2016