MEPS 593:155-171 (2018)  -  DOI: https://doi.org/10.3354/meps12486

ABSTRACT: Emperor penguins Aptenodytes forsteri are important predators in the Ross Sea ecosystem, yet little is known about their movement and foraging behavior outside the breeding season or within different demographic groups. In early March 2013, we instrumented 20 non-breeding emperor penguins in the eastern Ross Sea with satellite-linked recorders and analyzed their habitat preference and dive behavior. Track length ranged from 273 km to nearly 9000 km and dive data were obtained for over 96000 dives (mean maximum depth: 90.2 ± 77.8 (SD) m, mean dive duration: 4.6 ± 2.3 min), 17 of which exceeded the previous duration record of 27.6 min. Overall, emperor penguins preferred areas north of Cape Colbeck that were beyond the shelf break and received more sunlight. In these areas, penguins performed dives that were deeper, longer, faster, and more pelagic than dives located near the colony. Birds exhibited various movement and foraging strategies (‘shelf’ and ‘gyre’; benthic and pelagic). The occurrence of deeper and longer dives during the day (n = 28318) and at twilight (n = 60171) than at night (n = 7582), especially at high latitudes, is consistent with emperor penguins being visual predators. Observed differences in both movement and dive behavior as a function of light may indicate a change in prey preference across space and time. Our study offers novel insight into the habitat preferences and dive behavior for a previously unstudied demographic group, at a time when emperor penguins experience the most severe environmental conditions of their annual life cycle.

KEY WORDS: Emperor penguin · Tracking · Molt · Habitat suitability · Diving · Light · Foraging · Ross Sea