Harbour seal vigilance decreases over time since haul out

Abstract

The hypothesis was examined that vigilance of harbour seals, Phoca vitulina, on haul-out sites decreases with time since haul out. The study was conducted in the Bay of Fundy, Canada, where the seals haul out onto newly exposed rocky ledges on falling tides. Initial scanning time of newly hauled-out harbour seals during the first 3 min after haul out decreased as group size increased. The scanning times of individual seals significantly decreased over time since haul out. Alternating observations (similar conditions for each pair of seals) showed that newly hauled-out seals scanned significantly longer than seals that were resident for over 30 min. Seals on the periphery of the group scanned significantly longer than those in the centre. Part of the scanning decrease of seals in larger groups was attributed to time since haul out and fewer animals being on the periphery of the group. The seals were 1.4±0.6 ( sd) body lengths from the water's edge and 1.6±0.5 body lengths apart; 81% were oriented towards the water; this orientation and spacing allowed for ready access to the water. These behaviour patterns, and the high levels of vigilance, support an anti-predator function of harbour seal grouping on haul-out sites. 1996 The Association for the Study of Animal Behaviour