SOCIAL EFFECTS OF SPACE AVAILABILITY ON THE BREEDING-BEHAVIOR OF ELEPHANT SEALS IN PATAGONIA

The Patagonian breeding colony of southern elephant seals, Mirounga le onina, of Peninsula Valdes, Argentina is characterized by long, contin uous, homogeneous and spacious beaches. Reproduction in this colony oc curs at the lowest group densities reported for the species. The avail ability of ample space resulted in the dispersion of reproductive fema les along 160 km of coastline, with a range of 0-300 reproductive indi viduals per km. Females grouped together in small harems (median=11 fe males, range 2-122, N=432), and individual distance between females wa s one to two female body lengths. Body contact within the harem was ra re. Consequently, agonistic interactions (AIs) between females and fem ale aggression (Ag) towards alien pups occurred infrequently (median r ate=4 AIs/female per 100 h and 1 Ag/pup per 100 h, respectively). Pup mortality rate was low for an elephant seal rookery (3.5% for 3487 pup s). Most dead pups were stillborn, and only three of 38 pups whose cau se of mortality could be determined died from trauma or starvation fol lowing mother-pup separation. Female dispersal allowed many males to h ave access to females. About 45% of all males of reproductive size in the colony (about 1000 individuals) had a harem. Most adult males mate d with receptive females. Low-density breeding conditions benefited fe male reproductive success through an increase in pup survival. Female dispersal resulted in small harem size, however, and limited the poten tial for polygyny. (C) 1996 The Association for the Study of Animal Be haviour