Aggression in the Black Swan

Abstract

This paper gives initial results of a field study of the Black Swan to investigate the hypothesis that aggression functions to space out individuals over a resource. Spacing-out is designed as one bird increasing or maintaining the distance between itself and another. Probably aggression is usually connected directly or indirectly with a resource such as food or water. Among feeding swans aggression is common and increases as the flock increases but probably does not space out individuals over the food. Rather, there appears to be direct competition for food either for short-term individual gain or for long-term adaptive gain. At high densities the situation changes and the resource only indirectly influences the occurrence of aggression in so far as it causes crowding. A scarce resource leads to crowding and the reduction of individual space to a minimum. Aggression maintains that individual spare and thereby spaces out individuals over the resource. In such situations aggression is motivated primarily by factors internal to the individual and not by external actors connected to the resource. Internal factors also influence the occurrence of aggression in feeding flocks and cause highest occurrences when the birds are most hungry.