Barbosa and his colleagues tallied chinstrap penguins (Pygoscelis antarctica) in the Vapour Col colony of Deception Island, in the Antarctic's South Shetland Islands in 1991-92 and 2008-09. They photographed nests in 19 subcolonies, mainly in December when chicks were hatching. [See Photos of Chinstrap Penguins on Deception]
Results, which ended up including just 12 of the subcolonies due to availability of data, showed the occupied nests had declined by 36 percent between 1991 and 2008.
Barbosa and colleagues ruled out research activity as the cause for the loss since both studied populations and those used as controls showed similar patterns of decline.
Tourism is also not a likely culprit. Deception Island, built on a volcano, is one of the most visited places in Antarctica; the 2007-08 year saw some 25,000 visitors, according to the International Association of Antarctica Tour Operators (IAATO). Meanwhile, the nearby chinstrap penguin colony of Bailey Head, which is usually visited by 2,000 to 3,500 people every season, showed a decline of about 50 percent.
Rather, a dip in the krill population may be to blame, an idea supported by the fact that Adélie penguin population (P. adeliae) in the region is also declining, while the gentoo penguin population (P. papua), which has a more variable diet, is not.
(The chinstrap, gentoo and Adélie penguins are the three pygoscelid species (in the Pygoscelis genus) that inhabit the Antarctic Peninsula, the region of the Antarctic continent where the effects of climate change are more evident, the researchers noted.)