Climate change seen as likely factor
By Bob Berwyn
SUMMIT COUNTY — British scientists in Antarctica have documented the disappearance of an emperor penguin colony from an island near the west coast of the Antarctic Peninsula. The area has warmed significantly in recent decades and the researchers said a decrease in seasonal sea ice duration may be a key factor in the loss of the colony on Emperor Island.
The changes in sea ice duration are driven by regional climate change around the Antarctic Peninsula, where air and sea temperatures have warmed significantly in recent decades. Taken all together, the signs are compelling that the disappearance of the emperor penguin colony can be traced to climate change impacts, said Dr. Phillip Trathan, head of the British Antarctic Survey’s conservation biology program.
“We looked at alternative hypotheses of why the colony may have disappeared but found little evidence to support these other suggestions,” Trathan said.
In the bigger picture, researchers have also been documenting shifts and losses in populations of other ice-dependent penguin species like Adelies, while other species — like Gentoos — that don’t need ice have expanded their range, Trathan said.
The small colony of about 150 breeding emperor pairs on Emperor Island — one of the Dion Islands — was discovered in 1948. The population remained stable until 1970, when the numbers started to decline. By 1999, fewer than 20 pairs remained. In 2009, high-resolution aerial photography showed no remaining trace of the colony.
The loss of the colony offers empirical evidence for previous studies showing the vulnerability of emperor penguins to changes in sea ice duration and distribution and may serve as an early warning for other penguin emperor populations, Trathan said.
Efforts are under way to conduct a continent-wide population survey, he added. Emperor penguins are found all around Antarctica, with nearly all colonies assembling on stable, fixed ice. Since the penguins depend on that fixed ice for about eight months of the year, late formation of the ice, or early break-up in the spring can reduce the chances of breeding success for vulnerable colonies.
The life cycle of the emperor penguins takes place in an exquisite balance with the rhythms of ice formation. Courtship, egg laying and incubation occur during winter, followed by hatching, brooding and crèche formation during spring and early summer. Both parents tend the chicks until they fledge, generally in late spring and early summer (November and December), when the ice breaks up into floes that drift with the wind and currents.
The recent rate of warming around the Antarctic Peninsula is much higher than in many other parts of Antarctica and elsewhere in the world, which could affect the food web both above and below the emperor penguins, Trathan said.
The rapid changes could result in mis-matches of ecological cycles, he said, adding that there is now compelling evidence to link the disappearance of the Emperor Island colony with climate change.
Trathan said the evidence for why the Emperor Island colony declined is compelling, but that we need other similar studies elsewhere if we are to reduce the uncertainty about the future of Emperor penguins.