Aggressive display and territoriality of the bateleur <i>Terathopius ecaudatus</i>

Abstract

Bateleurs exhibit an aggressive display to conspecifies that incorporates an ‘attack’ pattern; the display has a territorial function because it drives intruders away from the nest, usually by a gain in altitude by the intruder. Resident breeding adults typically displayed at adults of the same sex or any of the non-adult age-classes, and each sex displayed equally often. The intensity of adult aggression was highest during the incubation period and decreased thereafter. Territories were maintained throughout the year, even after breeding failure and in non-breeding years. Bateleurs seem to maintain territories mainly for feeding, but other causes of territory formation, such as mate, progeny or nest-site protection, are not discounted. The intensity of adult aggression towards non-adults may influence non-adult movements, local distribution, and abundance. Aggression by non-adults was infrequent and was considered to be ‘play’ behaviour.