Foraging flights and habitat use of nesting wading birds (Ciconiiformes) at Lake Okeechobee, Florida

I monitored the foraging flights of four species of nesting adult wading birds at Lake Okeechobee, Florida, from 1989-1992 during chick-rearing periods. Median flight distances were: Great Egret (Casmerodius albus, N = 356) 3.7 km, range 0.1-33.3; Snowy Egret (Egretta thula, N = 236) 2.8 km, range 0.1-29.8; Tricolored Heron (E. tricolor, N = 82) 2.4 km, 0.1-22.3; and White Ibis (Eudocimus albus, N = 286) 2.7 km, range 0.1-33.3. Flights at the lake averaged moderate to short in comparison to those monitored in other areas of the southeastern United States. I found little evidence that increasing foraging flight distances influenced levels of nesting success and nestling production. Tricolored Herons were the possible exception; linear regressions of annual median flight distances versus colony-specific estimates of nest success and productivity revealed significant negative relationships. The association arose primarily because flights during two seasons averaged longer and success lower at one colony. Instead of foraging nearby in agricultural field ditches along with Snowy Egrets and Great Egrets, Tricolored Herons at this colony frequently traveled relatively long distances to forage in natural habitats within the diked boundaries of the lake. The dike that surrounds the lake produces an abrupt transition between natural habitats on the lake and diverse natural and artificial habitats off the lake. Tricolored Herons that nested on the lake generally foraged within the diked boundaries of the lake, but the dike's presence may help ensure that the other species nesting on the lake have access to diverse foraging opportunities under a wide range of hydrologic conditions. For all species, patterns of habitat use shifted significantly in response to fluctuations of the lake stage. There was evidence that high lake stages and rising water increased the flight distances of Snowy Egrets and perhaps Great Egrets, and that interruptions in otherwise steady surface-water trends (rising or falling levels) increased the flight distances of White Ibises. However, the variety of accessible habitats was such that nesting birds usually could adjust their patterns of habitat use in response to changing hydrologic conditions without having to extend their foraging distances to a degree sufficient to reduce levels of nesting success and productivity. Instead, variation in the quality of habitats accessible under different hydrologic conditions probably did contribute to observed variation in nest productivity.