Evolving views of food-limitation in wading birds: differing implications of prey and foraging habitat

Several wading bird populations are reportedly food-limited. However, this limitation is best viewed as dynamic because wading birds are adapting to different degrees to the rapid anthropogenic changes occurring to many wetlands. We quantified the influence of one anthropogenic change, the introduction of non-native aquatic fauna, on the prey selection of the Wood Stork (Mycteria americana), Tricolored Heron (Egretta tricolor), Snowy Egret (Egretta thula), and Little Blue Heron (Egretta caerulea), in the Florida Everglades, USA, 2012-2014. Tricolored Heron and Snowy Egret prey composition was statistically similar across years, with the majority of prey biomass coming from large native marsh fish. Little Blue Herons also consumed native marsh fish, but they differed from the other two herons in that they consumed more invertebrates and non-native fish species. Wood Stork prey composition differed from the small heron diets, composed of sunfish and non-native fish species. Whereas small herons are restricted in foraging because of their specialization on marsh fishes, their short nesting cycles allows for the phenological flexibility to delay nesting within a dry season until foraging conditions are optimal. Conversely, Wood Storks with longer nesting cycles are more temporally constrained, but appear to have greater flexibility in prey species, foraging range, and foraging habitat. An increase in the proportion of non-native species in the diets of storks suggests that storks, more so than small herons, are exploiting and may be affected by the changing species composition of aquatic fauna in South Florida.