Scubaism

Ancient eggshell fragments show that Adélie penguins living in Antarctica switched from eating fish to krill around the time that humans began hunting seals and whales. The finding suggests that when humans removed krill-eating predators the penguins exploited the resulting shrimp surplus.

Steven Emslie of the University of North Carolina in Wilmington, and William Patterson of the University of Saskatchewan in Saskatoon, analysed more than 220 fossil eggshell pieces ranging from 100 to 38,000 years old, and compared them with samples from modern nests.

By comparing the proportion of certain forms of carbon and nitrogen in the shells with the proportions found in fish and krill, the researchers could tell what the birds had been eating.

Emslie expected to find changes in diet matching climate change. Instead, the penguin menu remained biased towards fish until about 200 years ago, when the birds switched to krill.

The switch might be explained by an increase in fishing, says David Ainley of the California ecological consulting firm H. T. Harvey & Associates. “Not only were whales and seals removed,” he says, “there was a massive removal of fish from the Scotia Sea and western Antarctic Peninsula region at the same time.” Many of these fish ate krill, so their removal would have further boosted krill supplies.

Their dietary flexibility demonstrates the penguins’ ability to adjust to large ecological changes, but that doesn’t mean they’ll survive the changes to come, says Hobson. “I remain a pessimist when it comes to how they may now cope with the onslaught of climate change,” he says.Krill is an attractive food for penguins because it is high in protein and tends to travel in swarms. “The birds can capture lots of high-energy prey in a short time,” says Emslie.