COMMUNAL ROOSTING OF THE CATTLE EGRET

Abstract

Roosting birds generally have two main requirements: protection from predators and shelter from adverse weather. The paper summarizes the results of some preliminary investigation into the significance of these conventions as they apply to Ardeola ibis. Communal roosting in birds has been little studied, and the function of this phenomenon is not yet understood. In A. ibis the whole advantage of social roosting cannot be explained only in terms of protection from predators, shelter for adverse weather and/or conservation of energy at night. Data are presented in support of the claim that in A. ibis an important, if not the main, function of communal roosting is in assisting individuals to maintain contact with each other. The value of this behaviour rests in more efficient finding and exploitation of localized food resources. It is suggested that the gregarious roosting of A. ibis has been evolved primarily in relation to the food situation, and that communal roosting can be viewed as an extension of the principle of feeding by enhancement.