SEASONAL AND SEX-RELATED VARIATION IN THE ACTIVITY PATTERNS OF COMMON SEALS (PHOCA-VITULINA)

Radio-telemetry was used to study common seal activity patterns around Orkney, and to assess the degree of individual, seasonal and sex-related variation in haul-out behaviour in 1984-86. (2) During the summer, both males and females hauled-out regularly, in a marked diurnal pattern, but there were differences in other aspects of their haul-out behaviour. (3) Males showed a marked change in their haul-out behaviour at the beginning of moult. At this time, they hauled-out every day and, consequently, male behaviour became more synchronous. The change in behaviour of the male followed in 1985 was closely related to changes in abundance at the haul-out site that he used over this period. (4) In contrast, females showed no sign of a similar change in behaviour at the beginning of moult, but appeared to spend more of their time at sea after lactation. (5) During the winter, seals appeared to spend more time in offshore waters, although they regularly returned to the inshore study area to haul-out. At this time of year there was no marked diurnal haul-out pattern. (6) There was a high degree of individual variation in the effect of the tidal cycle on activity patterns, which appeared to be related to tide-related changes in food and habitat availability. Overall, however, the tidal cycle had less effect on haul-out behaviour in summer, when strong circadian patterns were more important. (7) The variations in activity patterns found in this study are discussed in relation to seasonal changes in feeding activity and the demands of breeding and moult.