Maternal aggression in northern elephant seals: the effect of the pup

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Abstract
Female northern elephant seals (Mirounga angustirostris) were observed for three breeding seasons on Southeast Farallon Island to determine the effect of the pup on maternal aggression. For females that lost their pups before weaning them, the mean percentage of aggressive encounters started and won decreased after the death of the pup. A higher percentage of females moved away at the end of an aggressive encounter from females that ultimately weaned their pups than from females that ultimately lost their pups. There was, however, no difference between the two categories in mean percentage of aggressive encounters started and won. Among females that weaned pups in all three seasons, individuals did not win more encounters but differed in percentage of females that moved away and in mean percentage of aggressive encounters started as they aged. A number of variables were associated with an increased probability that a female would successfully wean her pup: early arrival date, having a high percentage of females that moved away, and a high mean percentage of aggressive encounters won. Raising a pup in an area of high female density or where animals had access to the beach were associated with a decreased probability of weaning a pup.