Distribution of emperor penguins' dive directions under the fast sea ice

Abstract

Emperor penguins Aptenodytes forsteri feed mainly on Pleurogramma antarcticum and Pagothenia borchgrevinki in the sea of Antarctica. Because these prey are not distributed uniformly, prey encounter rates during a dive change depending on where emperor penguins dive. In limited time and space, they should select areas in which prey are expected to be abundant. We hypothesized that the distribution of emperor penguins' dive directions was not uniform due to their selective dives. In order to test this hypothesis, dive paths were calculated with the data recorded by data loggers. Dive direction was obtained for each dive path, and the distribution of the dive directions was investigated. In five experiments of the total of six experiments, the dive directions were not distributed uniformly. This suggested that the emperor penguins had a preference about their dive directions. The dive directions were not related with ocean current direction, which was considered to be one of the factors affecting penguins' diving behavior. The emperor penguins may have decided where they dived according to their knowledge about prey distribution and/or the behavior of conspecific individuals.