Influence of plumage colour on prey response: does habitat alter heron crypsis to prey?

The foraging strategies of wading birds may be influenced by their degree of crypsis to aquatic prey. White plumage has been hypothesized to be adaptive for herons hunting in open water habitats. We tested this hypothesis with laboratory and field experiments with multiple prey species. We investigated the response of crayfish, Procambarus spp., and mosquitofish, Gambusia affinis, to white- and dark-plumaged birds in an experimental chamber. We compared the time spent by a prey in front of a snowy egret, Egretta thula, mount, little blue heron, E. caerulea, mount, and a control (dowel) with and without backdrop vegetation. Mosquitofish tended to spend less time under the little blue heron mount with no backdrop present but made no observable response to either plumage colour against a vegetative backdrop. We assessed prey response in the field using three drop traps. Each trap had either a little blue heron mount, a snowy egret mount or a control (dowel) mounted underneath a trap. We compared the amount of biomass captured between treatments. More prey biomass (mosquitofish, crayfish and anurans) was captured under the control and snowy egret treatments than under the little blue heron treatment. Our results suggest that dark plumage may be a disadvantage to herons foraging in open water. In vegetation, structural complexity of the habitat appears to nullify differences in plumage colour between white and dark foraging herons.