The influence of social experience on the development and fixation of the form of displays in the black-headed gull

Abstract

Previous studies have shown that the form of the species-specific displays in young black-headed gulls, Larus ridibundus, gradually emerges, via incomplete patterns, to the final complete adult form. These incomplete patterns were almost exclusively performed during social interactions with conspecifics. This study investigated the role of experience, especially social experience, gained during the performance of incomplete display, and of imitation in the development of the complete form. The possible influence of these factors on the frequency and (stability of) form of display was manipulated by rearing chicks in different social contexts, after which the birds were re-housed in large groups of at least 10 birds. Stereotyped deviations in postures and calls were found in birds reared in groups of a few birds and their possible cause is discussed. No evidence for an influence of imitation was found. Although some birds reared in social deprivation developed the normal complete displays, the majority of the birds in this group showed a retardation in display development; after the birds were re-housed in large groups they made up for this by frequently performing incomplete display. This suggests that (social) experience, gained by the performance of these incomplete forms, fulfils a function in the development of complete display. However, display retardation is associated with a retardation in testosterone production, probably caused by lack of social stimulation. This suggests that incomplete forms of display may be epiphenomena of low levels of testosterone. Such levels are probably normally present in young gulls, and may gradually rise in ontogeny as the consequence of the many aggressive interactions these birds have on the territory. This may lead to the gradual emergence of complete display, after which these motor patterns become fixed in form.