Emperor penguin colonies characteristically use Antarctic sea ice for both breeding and foraging. In recent years, emperor penguins have moved onto ice shelves, which are composed of glacial ice and characterized by tall cliffs that are often thought too steep for this less-agile penguin species. Ice shelves are much more weather resistant and structurally reliable than sea ice, which is more weather dependent, seasonal and much thinner as it comprises the top layer of sea water during winter months. Fretwell et al. (2014) observed four colonies found breeding on ice shelves, and they recorded movement and foraging habits using satellite imagery during typical winter months over five seasons from 2008–2012. The penguins were generally loyal to breeding locations and when relocating, they relocated as a colony. Of the ice-shelf locations, those on which emperor penguins permanently resided over the course of the study were warmer in temperature, and the surrounding sea ice formed later into the breeding season after the colonies had already begun to use ice shelves. Submitted by Hilary Bruegl
Fretwell, P. T., Trathan, P. N., Wienecke, B., Kooyman, G. L., 2014. Emperor Penguins Breeding on Iceshelves. PloS one, doi:10.1371/journal.pone/0085285.
Peter T. Fretwell and colleagues collected data from known emperor penguin colonies located on ice shelves, a behavior not previously studied and only recently observed in this species. The colonies analyzed in depth were the Barrier Bay colony, located on the West Ice Shelf 5 km north of an ice gully used for ascending the cliff, the Shackleton Ice Shelf colony, located a secure distance from the ice edge of Shackleton Ice Shelf and characterized by a distinct, cyclical foraging route, the Jason Peninsula colony, located at the northernmost edge of the Larsen C Ice Shelf on the Antarctic Peninsula, and the Ruppert Coast colony, which only moved to the Nickerson Ice Shelf in 2012 after being observed on sea ice since 2008. The Barrier Bay and Shackleton Ice Shelf colonies have used ice shelves as breeding grounds consistently throughout observation since 2009 and 2008, respectively. The main group of the Jason Peninsula colony has been seen at their location on the ice shelf in satellite imagery since at least 2008, and it is accompanied by a smaller group that retains their breeding territory on sea ice just below the cliff of the ice shelf. To investigate a relationship between climate change and migration to ice shelves, Fretwell et al. used autumn sea ice concentration, mean temperature of each colony, and latitude of the colony locations.
Compared to all of the emperor penguin colonies in Antarctica, the Shackleton Ice Shelf and the West Ice Shelf were found to have the lowest sea ice concentration at the beginning of the breeding season, which is a viable reason that a colony would use more prominent ice shelves as a breeding location. The Larsen Ice shelf, while having only slightly below-average sea ice coverage, was exposed to higher than average temperatures and is located on the Antarctic Peninsula, the northernmost area of the continent. Many king penguins, which are known to be more agile than emperor penguins, climb dry continental shelves to stay cool when temperatures increase. A similar behavior in emperor penguins may be related to their transition to the ice shelf. Fretwell et al. found that the conditions of the Ruppert Coast colony location were neither warmer than average, nor was there less sea ice than average, and the colony is located farther south than average, indicating that the environmental factors recorded cannot explain the Ruppert Coast colony’s relocation in 2012.
The phenotypic plasticity exhibited by Antarctic emperor penguins will be to their advantage as climate temperatures continue to rise. Colonies that have not yet moved onto ice shelves may migrate in the future as sea ice becomes less reliable in autumn or chicks are unable to develop before ice shelves melt in spring. Other factors that accompany life on ice shelves, such as access to resources and shelter, may become a problem for emperor penguins in the future.