Of penguins' range and climate change.

Variations in the range of Adelie penguins along one section of Antarctica's coast during the past 45,000 years are a keen indicator of climate change there, a new study suggests.

Adelie penguins thrive only at sites with ice-free terrain, an abundant marine-food supply, and access to open water during nesting season, which starts each October, says Steven D. Emslie, a paleontologist at the University of North Carolina in Wilmington. To determine when such conditions occurred along the Ross Sea area of Antarctica, he and his colleagues carbon-dated Adelie bones, feathers, and eggshells from 21 active and abandoned nesting sites in that region,

At a penguin rookery on Cape Hickey, a site near the present-day edge of the Ross ice shelf, the scientists found samples dating back 27,000 to 43,000 years, a hint that during that period, as today, the Ross Sea was open water during the penguin-breeding season, says Emslie.

By contrast, a gap in the Adelie fossil record between 27,000 and 13,000 years ago at all sites along the Ross Sea that have been analyzed chronicles the northward advance of the Ross ice shelf during that period, Emslie and his colleagues argue in the January Geology.

Adelie penguins fully recolonized the Ross Sea coast only 8,000 years ago, after the most recent ice age ended, following the retreat of the ice shelf to near its present location. More-recent gaps in the fossil record at most sites in the area--one between 5,000 and 4,000 years ago, and another between 2,000 and 1,100 years ago--indicate periods when ocean conditions weren't favorable for penguin breeding and the climate was substantially cooler than it is now, the researchers speculate.