Predation as a Selective Force on Foraging Herons: Effects of Plumage Color and Flocking

Abstract

Abstract Experiments using model herons in natural mangrove habitats demonstrated that more hawks are attracted to white than to blue herons. Both Common Black-Hawks (Buteogallus anthracinus) and crocodiles (Crocodylus acutus) were observed preying on adult herons in Panama. Solitary herons were at greater risk than flocked foragers. White (immature) Little Blue Herons (Egretta caerulea) were attacked more frequently by hawks than were the blue adults of their species. Dark herons gave more alarms than white herons. Although flock size decreased in years of heavy predation and after attacks, mixed-flock composition remained the same. When flocks re-formed after hawk attacks, their members showed decreased foraging rates and increased interindividual distances. After repeated attacks, herons foraged in poorer habitats, under unfavorable climatic conditions, and under thermoregulatory stress. These results suggest that predation could be a potent force in maintaining color dimorphism in ardeids.