Penguins Breeding Later Due to Warming, Study Says

James Owen
for National Geographic News
Updated April 4, 2006
Antarctic seabirds are breeding later, because shrinking sea ice is
causing their food supplies to dwindle, a new study says.

Adélie penguins, Cape petrels, southern fulmars, and six other species were observed for the study.

The birds, which nest in East Antarctica, have delayed their spring arrival by an average of nine days and egg-laying by an average of two days over the past 50 years, according to polar researchers from the French National Center for Scientific Research in Villiers en Bois, France.

(Explore our interactive map of Antarctica.)

Study authors Christophe Barbraud and Henri Weimerskirch attribute this later breeding activity to decreases in sea ice caused by climate change.

The researchers say the disappearing sea ice, combined with a longer sea-ice season, has interfered with the birds' breeding cycle by reducing the amount of krill and other prey available in early spring in Antarctica. Because Antarctica's seasons are opposite those in the Northern Hemisphere, spring on the icy continent begins in October.

The study is based on data collected at seabird colonies between 1950 and 2004 in Adélie Land, on the eastern edge of the frozen continent.

The findings are published today in the journal Proceedings of the National Academy of Sciences.

Of the nine species studied, some arrived up to 30 days later than they had in previous years.

Despite much later arrivals, the birds are laying their eggs at pretty much the same time as they had in the past. In teh most extreme cases, birds were laying their eggs an average of 3.7 days later in the season than they had been 50 years ago.

(Watch video: Can Penguins Survive Warming?)

Lost Time

The relatively shorter delay for egg-laying suggests that the birds may now have a shorter window for raising their young and are having to make up for lost time, the scientists say.

One species bucked the general trend: the south polar skua, which hunts mainly penguin chicks and eggs. The other birds forage at sea for fish, squid, and krill (small, shrimplike crustaceans).

The researchers note that a 12 to 20 percent decrease in sea ice has been recorded in eastern Antarctica.

Previous studies have linked reduced ice cover to declines in krill and other marine organisms that Antarctic seabirds eat.

"All petrel and penguin species feed on crustaceans—krill, notably—and fish species whose abundance is linked to sea ice extent," said ornithologist Barbraud.

"Krill abundance increases with sea ice," he added.

Ice provides krill a refuge from predators. And algae—an important food source for krill—grows on the ice's underside.

Generally there may be less sea ice off East Antarctica. But the ice season here is actually growing longer, and that could also be delaying the arrival of seabirds at their colonies.

Barbraud said the sea ice season has lengthened since the 1970s "but only in East Antarctica. This is probably due to a change in atmospheric circulation."

Upside Down

The trend in East Antarctica is the opposite of that in the Northern Hemisphere. There, European and North American birds have been migrating and breeding earlier in the spring—a change that some scientists have also linked to global warming.

Keith Reid of the British Antarctic Survey (BAS) said, "That this breeding trend in Antarctica appears to be opposite to what we see in the Northern Hemisphere is intriguing but perhaps not entirely surprising."

Reid says that animals and plants in Europe and North America tend to synchronize their spring activity with warmer weather—once temperatures go up high enough, they're off.

Birds that breed in Antarctica, though, are dependent on what's happening to the sea ice.

"We know sea ice in various parts of the Antarctic behaves differently, and that the distribution and abundance of sea ice has changed differently," he said.

For this reason, Reid says, later-breeding seabirds in eastern Antarctica may be responding to local conditions. Colonies on other parts of the continent probably wouldn't be affected in the same way, he adds.

But the BAS researcher says reduced food availability is known to reduce the breeding success of Antarctic seabirds generally.

"If the birds get squeezed during the window when the food's available, that could have big implications for where and when the birds are able to nest in the Antarctic," he added.

Study co-author Barbraud says data from Adélie Land suggest "that a chronic decrease in sea ice will lead to a decrease in the population sizes of most of these species of seabird endemic to Antarctica."

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