Satellite telemetry suggests significant regional variation in post-fledging survival of Adélie penguins

Abstract Post-fledging periods represent one of the most vulnerable stages for juvenile seabirds. Adélie penguins Pygoscelis adeliae must quickly develop foraging skills while minimizing predation risk immediately after fledging. In the Antarctic Peninsula (AP) region, where populations are declining, previous studies have suggested that an acute post-fledging survival bottleneck exists. To assess the generality of survival bottlenecks, we compared published satellite tracking data from the AP with new data from 15 juveniles tracked for up to 152 days in Lützow-Holm Bay (LHB), east Antarctica, where populations are increasing. A small subset of these juveniles was equipped with dive-recording transmitters to examine the development of diving behaviour. Our results showed that transmitter signal loss progressed gradually, with no sharp decline in survival immediately after fledging in LHB. Cox proportional hazards analysis indicated that the juvenile mortality risk in the AP was four times higher than that in LHB. Dive data from three juveniles showed that maximum dive depth increased progressively, reaching up to 40 m, 10 days after fledging. These results suggest that regional differences in juvenile mortality risk are associated with predator distribution and sea-ice conditions, and that underdeveloped diving ability immediately after fledging may contribute to elevated early mortality.