Abstract. The relationship between size, dominance and copulatory success was
investigated in male northern elephant seals to determine the importance of size in male
intra-sexual competition for mates. The study was conducted over four breeding seasons at
the Año Nuevo rookery in central California. Mass was estimated using a photogrammetrical
technique in three seasons and measured directly in one. Copulatory success was positively
correlated with size (mass and length). This correlation was mediated through the positive …

The study was conducted over four breeding seasons at the Ano Nuevo rookery in central
California. Results support the hypothesis that male reproductive success in this species is
principally determined by dominance rank, which, in turn, is affected by male size. However,
they also suggest that large size is just one of a number of important factors that affect the
outcome of male intra-sexual competition and hence, reproductive success.