Aggression in the Black Swan

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SUMMARY Tingay, A. 1974. Aggression in the Black Swan. Emu 74: 35–38. This paper gives initial results of a field Study on the Black Swan to investigate the hypothesis that aggression functions to space out individuals over a resource. Spacing-out is defined 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 space 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 factors 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.

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