Migratory movements and winter diving activity of Adelie penguins in East Antarctica

Seabirds breeding on the Antarctic continent must cope with extreme changes in sea ice cover and day length throughout the year. Adélie penguins are expected to adjust their migratory movements and diving activity to seasonal changes in foraging conditions, but their winter diving activities have not been examined previously. Here, we tracked 18 and 5 Adélie penguins by using geolocators with and without depth sensors, from a colony in East Antarctica over 2 winter seasons. After breeding, all but one penguin migrated westward from March to April, then moved northward from May to August as the sea ice edge extended to the north, then moved southeastward, returning towards the breeding colony. Migratory movements followed sea ice movements and the seasonal extension in this region, which is influenced by the west-flowing Antarctic Slope Current and wind. Penguins dived deeper during winter, reaching a maximum depth of 129 m. The birds dived mostly between civil dawn and dusk, and tended to stay on ice overnight. Diving effort (total time spent underwater per day) did not decline with sea ice concentrations, suggesting that penguins found open water to dive even with >90% sea ice cover. Diving effort was lowest around the winter solstice, but was relatively high before and after the annual moult, and also before the start of breeding when birds presumably needed to accumulate body reserves. Our results highlight how the migratory movement and winter diving activity of Adelie penguins are closely associated with the seasonal polar environment.