Are environmental factors responsible for changed breeding behaviour in emperor penguins?

Abstract

Emperor penguins (Aptenodytes forsteri Gray) are the only vertebrate species that breed during the Antarctic winter. From the beginning of the breeding season in April until fledging of the chicks in January, emperor penguins rely on the stability of sea (fast) ice. The International Union for Conservation of Nature (IUCN) has recently listed the species as ‘near threatened’ because the habitat of emperor penguins may deteriorate significantly over the coming years with the anticipated changes in sea ice conditions due to climate change. Since 2009, four emperor penguin colonies have been observed on ice shelves, as opposed to sea ice, during the breeding season (Fretwell et al. 2014). This striking change in their breeding behaviour was interpreted as an adaptation of emperor penguins to poor sea ice conditions. Here we report that a large part of the emperor penguin colony at Atka Bay (Dronning Maud Land, Antarctica) moved onto the ice shelf during the 2013 breeding season. This colony has been regularly observed since 1981 but has never before been seen breeding, incubating their eggs, brooding or creching on the ice shelf. Our observations concur with a recent report, which documented that altered breeding behaviour in emperor penguins has occurred almost simultaneously across Antarctica (Fretwell et al. 2014). Interestingly, the sea ice at Atka Bay has been stable for three consecutive seasons and thus cannot have triggered this change in behaviour. Rather, we present evidence of increased snow accumulation that has greatly improved the accessibility of the ice shelves around Atka Bay, and we discuss additional meteorological factors and local topographical conditions that may have contributed to the shift in breeding location from sea ice onto an ice shelf.