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Social behaviour in a non-pupping colony of steller sea-lion (Eumetopias jubata) Harestad, Alton Sidney

Abstract

Eumetopias jubata is polygyncus. The sea-lions segregate during the breeding season into pupping colonies consisting of adult males and females, and non-pupping colonies consisting mainly of sub-adult males. All previous studies of the social behaviour E. jubata have been concerned only with pupping colonies. This study describes the social behaviour and organization of a non-pupping colony. The colony is located at Mclnnes Island, British Columbia (Lat. 52°16’ N., Long. 128°43’ W.). It consists of 100-150 animals. They are mainly sub-adult males though several adult sea-lions of both sexes were present. Data concerning six age-sex classes were taken using two methods. One method involved the development of an ethogram consisting of 34 behaviour patterns and the observation of social interactions. The other method involved spacial organization and activity. Qualitative notes on territorial and reproductive behaviour as well as population structure were also recorded. A peck-dominance hierarchy exists between the classes and is related to many of the behaviours measured. Males are more socially involved than females. This is more voluntary for males than it is for females. As males mature their behaviour becomes more complex than that of females. Females are not aggressive. This is reflected by their lack of Body Contact behaviour. Males are aggressive towards other males and use more Body Contact behaviour than females. Body Contact behaviour is mainly physical aggressive interaction. As males mature it is replaced with Non-body Contact behaviour which is largely threats and displays. The intense social conditioning of sub-adult males results in more socially adept adults that are better able to cope with the complex society at pupping colonies. Sub-adult males are not territorial. However, some adult males are. This is related to the presence of females. Territories act as refuges for females who avoid areas of activity and harassment by sexually mature sub-adult males. This contributes to the grouping of females around territorial adult males. Non-pupping colonies are spatially organized similar to pupping colonies except for the relative proportion of age-sex classes. Socially, non-pupping colonies are less organized than pupping colonies. Social organization in E. jubata is promoted by the tranquil behaviour of adults and inhibited by the disruptive behaviour of sub-adult males.

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