http://worldcat.org/entity/work/id/430780222

Temporal and social aspects of the foraging ecology of a piscivore, the osprey (Pandion haliaetus)

I conducted a year-around field study on foraging behavior of a resident population of ospreys (Pandion haliaetus) at Newnan's Lake, Alachua County, Florida, from 1985-1986. I examined (i) foraging behavior of adult ospreys in relation to temporal variation in available prey, and (ii) temporal and social aspects of the ontogeny of foraging. I also monitored dynamics of the fish resource base at the study site. Adult foraging behavior varied considerably over the 18-month study period. Ospreys preferred sunfish (Lepomis spp.) from March-July each year, but preferred shad (Dorosoma spp.) from September -March. Bass (Micropterus salmoides ; Morone saxtilis) were captured in proportion to their abundance. Seasonal shifts from shad to sunfish were strongly associated with increases in sunfish relative and absolute abundances. Once sunfish abundance declined, ospreys switched back to shad. Relative to sunfish, measures of shad abundance and variability were more constant, suggesting that shad represent a more stable resource base. Time lags between change in prey abundance and shifts between prey types may be due to the inability of ospreys to respond immediately to changes in the prey resource base. Adults preferentially hunted in the littoral zone of the lake from May-July each year. From August-April, ospreys hunted in pelagic habitat, although preference for pelagic habitat was not statistically significant. Use of littoral habitat was strongly associated with an increase in the abundance and availability of sunfish. Young ospreys initially captured fish in proportion to their availability by species and size class, ignoring only the larger size class of all fish species. Individual differences in preference patterns existed between unrelated young. Siblings, however, hunted together and had statistically similar prey preference patterns throughout post-fledging. Use of fish resources and foraging mechanics of birds with siblings also approached that of adults at a faster rate than lone birds. Similar resource use and faster rates of learning between siblings suggests post-fledging interactions may facilitate the development of foraging skills.

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