HOMING BEHAVIOR OF JUVENILE NORTHERN ELEPHANT SEALS

The aim of this study was to determine if juvenile northern elephant s eals, Mirounga angustirostris, translocated from their rookery would r eturn to it quickly and reliably. During the spring and fall of 1990 a nd 1991 we captured 75 seals at Ano Nuevo State Reserve, CA, U.S.A, an d translocated them to release sites up to 100 km away. Eighty-eight p ercent of the seals returned to the capture site within 4.7 +/- 4.3 d. Homing rate increased with age, but even the youngest seals (8-10 mo) homed at a 73% rate. Homing rate did not vary significantly with sex, season, or year. Data from diving instruments suggested that the seal s often followed direct routes home, arrived on the rookery significan tly more often at night than during the day, and when released togethe r, returned separately. Mean homing speed of 18 seals with complete di ving records was 39 km/d (range 3-70 km/d). Instruments on seals had n o detectable effect on homing rate or homing speed. The translocation paradigm provides a powerful tool for conducting intensive shortterm s tudies on free-ranging seals.