The Adélie Penguin (Pygoscelis adeliae), a close relative of the Chinstrap Penguin (P. antarctica), nests on ice-free rocky coasts around Antarctica. It tends to occupy higher ground than does the less colonial Gentoo Penguin (Pygoscelis papua). Adélie Penguin colonies are typicaly large and are thus often located in extensive open areas, sometimes far from the open sea. Adélie Penguins feed mainly on krill (Euphausia superba, E. crystallorophias), along with smaller quantities of fish, amphipod crustaceans, and cephalopods (squid and relatives). Although these penguins generally hunt at depths less than 20 m, they have been recorded as deep as 175 m. Adélies typically arrive at their breeding colony in September or October and most eggs are laid in November. Colonies may be enormous, with densely packed nests, and may include Gentoos and Chinstraps, but the Adélies tend to cluster together in the colony. Two eggs are deposited in the simple nest (a small depression lined with pebbles). Eggs are incubated by both sexes for 30 to 43 days, broken into stints of 7-23 days. The young gather together in creches starting around 16 to 19 days and fledge at 50 to 56 days. They are sexually mature by 8 years (rarely at 5 and exceptionally at 3). After breeding, birds move north toward rich feeding grounds. Adults do not molt at the colony, but rather on ice floes. (Martínez 1992) Dunn et al. (2011) used ARGOS satellite telemetry and Global Location Sensors (geolocators) to identify the molt locations and winter foraging dispersal of Adélie penguins after they left their breeding colonies on Signy Island in the South Orkney Islands. They found that the birds remained away from colonies (at distances up to 2235 km) for around 9 months (Ballard et al.  report that Ross Island Adélies make the longest migration known for this species, traveling as far as 17,600 km round trip between autumn and spring). Dunn et al. found that molt took place within the pack ice during February and March within a narrow latitudinal range (65 to 71 degrees S), at a mean distance of 126 km from the ice edge; the mean duration of individual molt was around 18.6 days. After molting, the birds spent the subsequent winter months moving north or northeastward within the expanding winter pack ice, at a mean distance of 216 km from the ice edge, and in areas with ice cover > 80%. Dunn et al. note that the dependence of Adélie Penguins on sea ice habitat suggests that any further reductions in sea ice extent in the Weddell Sea region would potentially have important impacts on Adélie Penguin population dynamics. Ballard et al. (2010) studied changes in annual migration patterns of Adélie Penguins through time. They suggest that although these penguins have had to modify their life history characteristics and movements through the millenia as ice ages have come and gone (with coincident changes in breeding and sea ice habitat), the current rate of habitat change may be unprecedented for this species.
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