Sexual Behavior in the Northern Elephant Seal Mirounga Angustirostris

AbstractThe mating behavior of Northern elephant seals, Mirounga angustirostris, was studied during the I968, I969 and I970 breeding seasons at Año Nuevo Island, I9 miles north of Santa Cruz, California. Copulation takes place primarily on land, from January to March; it is initiated and terminated by the male and lasts approximately 5 minutes. A few males do most of the breeding and the higher a male's rank in the social hierarchy, the more frequently he copulates. Some bulls may maintain high rank and participate in mating for 3 breeding seasons. Low ranking males are kept out of the harem so they attempt to copulate with females on the periphery or in the water with departing females. Males prevent subordinates from mounting females and disrupt copulations in progress. The higher a male's rank, the more freedom he has to copulate without interference, and the more frequently he interferes with the copulation of others. The highest ranking males interrupt their own copulations prematurely to attack other males and prevent them from copulating. Males mount weaned pups, yearlings, and non-estrous females in addition to estrous females; the latter are mounted most frequently. Females come into estrus 24 days after parturition. They are receptive for about 3 days (range I-I3 days), during which they may copulate several different times with one or more males. Females are usually in estrus when they leave the rookery and return to sea. The greatest difference in the copulatory pattern of the elephant seal, a true seal, and members of the sea lion family, is that the former interfere with the copulations of other males while the latter do not. This may he due to differing social systems, a social hierarchy in elephant seals and a territorial system in sea lions. In elephant seals, where copulations are interrupted, mating may be incomplete. This is not as likely with sea lions where copulations are never interrupted because males honor the boundaries of their neighbors. The differences in female behavior and sexual physiology - a long promiscuous estrous period in elephant seals as opposed to a brief estrus with only one copulation in sea lions - may have evolved as a compensation for the consequences of the social behavior of males.