Scale-Dependent Habitat Selection of Nesting Great Egrets and Snowy Egrets
2007
Stolen, Eric D. | Collazo, Jaime A. | Percival, H. Franklin
Foraging habitat selection of nesting Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) wasinvestigated within an estuary with extensive impounded salt marsh habitat. Using a geographic information system,available habitat was partitioned into concentric bands at five, ten, and 15 km radius from nesting colonies to assessthe relative effects of habitat composition and distance on habitat selection. Snowy Egrets were more likely thanGreat Egrets to depart colonies and travel to foraging sites in groups, but both species usually arrived at sites thatwere occupied by other wading birds. Mean flight distances were 6.2 km (SE = 0.4, N = 28, range 1.8-10.7 km) forGreat Egrets and 4.7 km (SE = 0.48, N = 31, range 0.7-12.5 km) for Snowy Egrets. At the broadest spatial scale bothspecies used impounded (mostly salt marsh) and estuarine edge habitat more than expected based on availabilitywhile avoiding unimpounded (mostly fresh water wetland) habitat. At more local scales habitat use matched availability.Interpretation of habitat preference differed with the types of habitat that were included and the maximumdistance that habitat was considered available. These results illustrate that caution is needed when interpreting theresults of habitat preference studies when individuals are constrained in their choice of habitats, such as for centralplace foragers.
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