Reproductive success of ospreys was used to evaluate the habitat quality of Florida Bay. We compared subpopulations that breed and forage exclusively in Florida Bay, an ecosystem suspected to have been impacted by human development, with those nesting adjacent to the bay on the mainline
keys and foraging in the Atlantic Ocean, a relatively undisturbed habitat. We also compared osprey reproduction on gulfside islands in the lower keys, which have a structure similar to keys in Florida Bay but are more affected by oceanic influences, with nest success on adjacent mainline keys.
Florida Bay ospreys produced significantly fewer fledglings per occupied, active, and successful nest than those on the upper mainline keys. In the lower keys, however, there was no significant difference between gulfside and mainline key nesting success. Ospreys nesting on the upper mainline
keys departed on foraging trips towards the bay and the ocean in nearly equal proportions. However, 47.2% of food deliveries came from the direction of the ocean while only 19.5% came from the bay. We conclude that access to the ocean plays a significant role in the greater reproductive success
of birds nesting on the mainline keys and suggest that Florida Bay ospreys are experiencing decreased reproductive success due to an inadequate food supply. These results support the contention that the osprey is a sensitive biological indicator.
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