Aggression and sexual activity of male Southern elephant seals, Mirounga leonina

The agonistic and sexual activity of individual male Southern elephant seals (Mirounga leonina) was studied during the breeding season at South Georgia. Harem bulls were older and larger than non-harem bulls and, although size and age are related, harem bulls were also larger than non-harem bulls of the same age. Large body size conferred advantages in fighting and the agonistic relationships of the bulls gave rise to a dominance hierarchy with access to harems and activity within harems, being determined by rank. Vocalizations were the most highly rank-related aggressive behaviours. The most common vocalization, the roar, probably functioned in both individual recognition and size assessment. Over 90% of encounters of high-ranked bulls were "walkovers" and only 4% of 4003 agonistic interactions nvolved physical contact.