Feeding Ecology and Prey Selection in the White Ibis

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Abstract
The American white ibis [E. albus] is a tactile-foraging, flocking predator that occupies a seasonally fluctuating environment in southern Florida, [USA]. The population makes extensive seasonal movements correlated with fluctuating water levels and changes in the availability of foraging habitat. Outside the nesting season, the ibis'' diet and habitat selection are highly variable. During nesting, food selection differs between inland and coastal colonies, especially in the relative importance of crustaceans. Nesting ibis consume neither the most abundant nor the most energetically valuable prey. They forage in locations where relatively high energy is available but, unlike wood storks [Mycteria americana], not when or where most prey species reach maximum seasonal concentrations. Some prey species are taken selectively in most habitats whereas other prey are underrepresented in the diet, as demonstrated by the ibis'' 2 most important prey, highly selected crayfish and under-selected fish. Ibis select prey passively before capture. Selectivity depends primarily on ability to catch specific prey types. The relation between abundance and consumption differed among prey. Consumption and abundance of crayfish were unrelated except when prey switching occurred in the presence of an extraordinarily high abundance of alternate prey, which may have competitively inhibited capture of crayfish. Prey taken in any situation depended on the types available and on a synergistic relation among them. Ibis increased efficiency of predation primarily by selection of foraging habitat. Colonial nesting, flocking, aggregative foraging, regional movement, variable colony site selection, dynamic nest timing and variation in size of the nesting population adapt this species to fluctuating environment.