MATERNAL-BEHAVIOR AND ENERGY INVESTMENT BY GREY SEALS (HALICHOERUS-GRYPUS) BREEDING ON LAND-FAST ICE

The grey seal (Halichoerus grypus) is a sexually dimorphic polygynous phocid that breeds in a synchronous fashion, within populations, on bo th sides of the North Atlantic Ocean. This study was designed to exami ne factors that may influence maternal behaviour and energy investment of females breeding on land-fast ice. The study was conducted on the ice around Amet Island, Nova Scotia, during the breeding seasons of 19 92, 1993, and 1994. Scan sampling and ad libitum observation technique s were used to record behaviour. Mass transfer from mothers to pups wa s determined using serial mass records for pairs. Rate of pup mass gai n was 2.5 +/- 0.6 kg/day and pup mass at weaning 50.0 +/- 7.3 kg. The duration of lactation was 15.2 +/- 1.6 days. Maternal mass at parturit ion was 210.6 +/- 23.8 kg and female mass loss during the lactation pe riod was 75.0 +/- 16.0 kg. This mass loss represented 35.7 +/- 6.1% of their parturition mass. Efficiency of mass transfer was 0.52 +/- 0.12 . Breeding habitat influenced maternal behaviour. Compared with land-b reeding grey seals, ice-breeding females had an intensified nursing pe riod, during which females transferred a similar amount of energy to t heir pups over a shorter time frame. Additionally, females on land-fas t ice gave birth more synchronously than is the case in land-breeding colonies. Date of parturition within the breeding season had some infl uence on female behaviour; females giving birth late in the season wer e more active than females breeding earlier. The behaviour of males ma y play a role in determining the optimum time for birthing. Adult male s spent more time engaged in agonistic behaviours late in the breeding season and the resultant disruption of adjacent females may serve as a selective force maintaining birthing synchrony. These influences als o apply in land-breeding situations and are not likely to contribute t o the contraction of the nursing period and the more synchronous breed ing observed among females on ice. The more condensed lactation and bi rthing periods are likely a response to the higher risk of premature s eparation on the ice.