The process of obtaining breeding territories and mating success in male northern fur seals was studied through a longitudinal survey in St. Paul Island, Alaska in 1993–1999. Resighting of metal tags that had been deployed to pups in their natal areas generally showed site fidelity of males to natal breeding areas, but also indicated movements within the breeding area. Males started to reside in the periphery of central breeding areas (CBAs) at age 7, and some males established breeding territories in the CBAs at age 7–9. Males bleach-marked in the peripheral areas showed a tendency to reappear in the same locations over successive breeding seasons. Some of them entered nearby CBAs in the late breeding season and held territories. Once adult males acquired breeding territories, they exhibited a strong tendency to return to the same locations in the following breeding season(s). Duration of the effective territory tenure after June 30 and the maximum number of adult females in a male's territory did not differ significantly between the first and second years of his territory tenure (P > 0.05). However, starting date of territory tenure became earlier in the second season (P = 0.04). The index of mating success estimated from the seasonal frequency distribution of copulations also increased significantly in the second years of territory tenure (P = 0.03). These results indicate that territory acquisition is a site-specific multi-year process in which males return to the same breeding area for successive breeding seasons and gradually shift their presence spatially to the center of the breeding aggregation and temporally to the peak season of female estrus. Prior experience formed through site fidelity is likely an important factor for territory acquisition and mating success in male northern fur seals.
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Vol. 30 • No. 1