Reproductive Success of Three Species of Herons Relative to Habitat in Southern Florida


We compared numbers of nesting pairs, clutch size, nest success, and production of young of Tricolored Herons (Egretta tricolor), Little Blue Herons (E. caerulea) and Snowy Egrets (E. thula) breeding in freshwater, estuarine, and marine habitats of southern Florida between 1986 and 1989. Tricolored Herons were commonest in marine habitats, while Snowy Egrets and Little Blue Herons were most common in estuarine and freshwater habitats, respectively. Among Tricolored Herons, we found no evidence for consistent differences in laying date among the three habitats, and no relationship between clutch size and laying date. Among Tricolored Herons and Snowy Egrets, clutch sizes were larger in freshwater areas than in either of the two saline habitats, with no consistent differences in clutch size between marine and estuarine locations. Survival of nests was consistently higher in freshwater and marine than in estuarine habitat, an effect largely attributable to heavy egg predation by Common Crows (Corvus brachyrhynchos) in estuarine colonies during incubation. Fledging success of Snowy Egrets and Tricolored Herons also was consistently higher in freshwater habitats than in either of the saline habitats. Thus, freshwater habitats showed generally increased nesting success and productivity over saline ones. Potential explanations for these differences among habitats include increased nest predation in estuarine colonies, a degrading estuarine and marine food web in the region, and the energetic constraints of salt excretion.

Colonial Waterbirds