SEXUAL-BEHAVIOR OF MALE NORTHERN ELEPHANT SEALS .1. LETHAL INJURIES TO ADULT FEMALES

Adult female mortality of northern elephant seals, Mirounga angustirostris, was monitored daily throughout the breeding season and weekly during the non-breeding season at Ano Nuevo, California, during the period 1968 to 1987. Behavioral observation and necropsy findings were collected and circumstantial evidence was compiled to determine the cause of death. Female deaths on the rookery were rare; only 17 female deaths were recorded over the 20 year period. Cause of death could not be estimated in three cases because of advanced decomposition, one female died from an accident, and two others had no apparent trauma. The majority of deaths (11) were caused by traumatic injuries inflicted by males during mating attempts as the females departed harems for the sea at the end of lactation. Mortalities caused by males were distributed across a broad age range. Based on the observed incidence of female mortality in relation to females present on the rookery, the probability of a female being killed by a male during the breeding season is about one in a thousand. Females are expected to evolve adaptations to reduce injurious encounters with males. Females are injured and killed by males during mating attempts in a variety of species. A hypothesis concerning the conditions under which female animals sustain potentially lethal injuries during mating is advanced.