Responding to Climate Change: Adelie Penguins Confront Astronomical and Ocean Boundaries

Long-distance migration enables many organisms to take advantage of lucrative breeding and feeding opportunities during summer at high latitudes and then to move to lower, more temperate latitudes for the remainder of the year. The latitudinal range of the Ad lie penguin spans ~ 22 deg. Penguins from northern colonies may not migrate, but due to the high latitude of Ross Island colonies, these penguins almost certainly undertake the longest migrations for the species. Previous work has suggested that Adelies require both pack ice and some ambient light at all times of year. Over a 3-yr period, which included winters of both extensive and reduced sea ice, we investigated migratory routes and characteristics and wintering locations of Adelie Penguins from two colonies of very different size on Ross Island, Ross Sea, the southernmost colonies for any penguin. We acquired data from 3-16 Geolocation Sensors affixed to penguins each year at both Cape Royds and Cape Crozier in 2003-2005. Migrations averaged 12,760 km, with the longest being 17,600 km, and were in part facilitated by pack ice movement. Trip distances varied annually, but not by colony. Penguins rarely traveled north of the main sea ice pack, and used areas with high sea-ice concentration, ranging from 75-85%, about 500 km inward from the ice edge. They also used locations where there was some twilight (2-7 hr with sun greater than 6 below horizon). We review how Adelie Penguin migration has likely changed since withdrawal of the West Antarctic Ice 35 Sheet across the Ross Sea beginning 12,000 yBP. If sea ice extent in the Ross Sea sector decreases, as predicted by climate models, we can expect change in wintering areas, the location of which ultimately may be limited more by the availability of adequate light for visual foraging than by the availability of suitable pack-ice.