CORVALLIS, Ore. - Adélie penguins live a long time, have a high survival rate, and as adults breed in the same location where they were raised as young, but when a change in their environment becomes severe enough, they aren't afraid to get out of Dodge and raise their own offspring elsewhere.
In a new study published in Proceedings of the National Academy, scientists document how the grounding of two enormous icebergs caused sufficient disruption to the lives of penguin colonies living on islands in the Ross Sea to force them to move to different locations to breed.
While this doesn't sound like a startling response, such behavioral adaptation among Adélie penguins, which are notoriously philopatric - or bound to their own birthplace when it comes to breeding - had only rarely been documented. It provides evidence about how these birds coped with past environmental change - and may cope with changes in the future.
"The study shows that the Adélie penguins have the capacity to radically alter their patterns - and that is welcome news," said Katie Dugger, an Oregon State University wildlife biologist and lead author on the study. "Obviously, they dealt with the advance of ice sheets in the past and thus have the ability to adjust to climate change in the future. Now we have some idea about how they do this."
Dugger and her colleagues had been studying Adélie penguins in the southwestern Ross Sea for several years as part of a long-term research project funded by the National Science Foundation when two large icebergs sheared off the Ross Ice Shelf in March of 2000 and lodged against Ross Island. In addition to forming a physical barrier, it also kept sea ice from breaking up in the southwest Ross Sea during some years.
This effectively cut off the population of penguins living at one of four study colonies (Cape Royds) from having easy access to the open ocean.
"Some of these birds had to walk up to 70 kilometers in some years just to get to the open water," Dugger pointed out. "Under normal conditions, Adélie penguins return to the nest every two to four days to feed their young. The addition of a long walk increased the time it took adults to get food, which didn't bode well for the survivability of the nests."
Though moving to a new colony for breeding has rarely been documented among Adélie penguins, scientists have suspected such behavior takes place because genetic tests on individuals from different colonies show more homogeneity than if distinct colonies had no intermixing.
Still, such behavior is rare and perhaps episodic, and the scientists plan to evaluate the breeding success of the penguins that have relocated, said Dugger, an assistant professor in OSU's Department of Fisheries and Wildlife. They also have many birds banded as chicks and are in the process of trying to understand how the iceberg affected movements of birds before their first breeding season, which happens between three and seven years of age.
"There are definite long-term benefits to staying in one place," Dugger said. "You learn the food resources, you know the nesting resources, you interact with the same neighbors - even in sub-colonies within the larger colony. To abandon all that requires a significant stressor, such as a change to the environment. But if the change is big enough, the penguins will move."
Other authors on the study include David Ainley, H.T. Harvey and Associates of Los Gatos, Calif; Phil Lyver and Kerry Barton, Landcare Research of New Zealand; and Grant Ballard, of PRBO Conservation Science in Petaluma, Calif., and the University of Auckland in New Zealand.
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Katie Dugger, 541-737-2473