MOTHER - PUP REUNIONS IN HARP SEALS, PHOCA-GROENLANDICA - CUES FOR THE RELOCATION OF PUPS

This study was designed to examine how female harp seals (Phoca groenl andica) solve the orientation problems they face when returning to the ir pups from the water in a pack-ice environment. Data were collected during the breeding seasons of 1992 and 1993 in the Gulf of St. Lawren ce, Canada. During 31 h of observations, 73 returns of females were do cumented. Most return paths of females from the water originated at th e access point closest to their pup (88%), indicating good underwater orientation capabilities. The mean path length was 1.3 +/- 2.2 times t he length of a direct line between the water access point and the pup, and most females were clearly oriented toward their pup upon leaving the water. Most return paths (84%) terminated in a nursing session wit h the pup. Prior to nursing, naso-naso contact was made by the mother- pup pair. Only 26% of return paths were directed toward a calling pup, the rest were spontaneously performed to a silent, unmoving pup. The mean duration of calling prior to the appearance of the female was 7.3 +/- 7.2 min (N = 18). Mothers returning to a vocalizing pup did not h ave more direct return paths than those returning to a silent pup (Man n-Whitney U test, U = 422, P = 0.19). Although pups were remarkably se dentary in the absence of their mothers, approximately half of females returning to their pup (32/73) were approached by it. Only 7% of path s (5/73) of females involved contact with a foreign pup. Likewise, pup s rarely approached females other than their mother. Females were able to return directly to sleeping, silent (or dead) pups that were not v isible from the origin of the path and were able to return to location s where they had last left the pup without the pup itself acting as a stimulus. Thus, it appears that harp seal mothers use multimodal senso ry cues to return to their pups in the pack-ice environment. At long d istances spatial information appears to be of primary importance and c an be used exclusively by females to return to specific positions on t he ice. Visual and auditory cues emitted by pups may ease the task of relocation, although they must be considered of secondary importance. Pups appear to recognise their mothers at a distance. At close range, olfactory cues provide the definitive means of individual identificati on within mother-pup pairs.