February 19, 2009
Changing ocean conditions turning penguins into long-distance commuters
Imagine you live in the suburbs of Chicago and you must commute hundreds of miles to a job in Iowa just to put food on the table. Magellanic penguins living on the Atlantic coast of Argentina face a similar scenario, and it is taking a toll.
The penguins’ survival is being challenged by wide variability in conditions and food availability, said Dee Boersma, a UW biology professor and a leading authority on Magellanic penguins.
For example, while one parent incubates eggs on the nest the other must go off to find food. But these days, Boersma said, penguins often must swim 25 miles farther to find food than they did just a decade ago.
“That distance might not sound like much, but they also have to swim another 25 miles back, and they are swimming that extra 50 miles while their mates are back at the breeding grounds, sitting on a nest and starving,” she said.
Boersma has recently published research documenting some of the serious challenges faced by Magellanic penguins in a colony at Punta Tombo, Argentina, that she has studied for more than 25 years. She discussed her research last week during a symposium at the American Association for the Advancement of Science meeting in Chicago.
The Punta Tombo colony has declined more than 20 percent in the last 22 years, leaving just 200,000 breeding pairs, Boersma said.
There are several reasons for the decline, including oil pollution and overharvesting of fish by humans. Climate variation also is a major problem, she found.
Longer trips for food during a given breeding season lessen the chances that a given penguin pair will successfully reproduce. Some younger penguins move to colonies that are closer to food one year but might be farther away from food the following year. Increased ocean variability means penguins often return to their breeding grounds later and are in poorer condition to breed.
They also are increasingly subject to having their desert nests flooded by rain. Five times in the last 25 years, Boersma said, the Punta Tombo reserve has recorded about 2.5 inches of rain between Oct. 15 and Dec. 16, which threatens the survival of eggs and small chicks.
“That turns their little nests into swimming pools,” she said.
In addition, there have been increasing instances of El Nino-like events that alter ocean currents, forcing penguins to travel farther for the fish on which they feed. Increasingly, Boersma has found that penguins she tagged at Punta Tombo years ago are turning up in colonies as much as 250 miles farther north. Birds migrating in search of food are forming the new colonies, but often they end up on land that is not part of a government preserve like Punta Tombo is.
The problems don’t just confront Magellanic penguins, said Boersma, director of the Wildlife Conservation Society’s Penguin Project. Of 17 penguin species, 12 are experiencing rapid population declines. The least concern is for the emperor, king, Adelie, little blue and chinstrap penguins, she said. All the rest are nearly threatened, threatened or endangered.
She noted that the success of Argentine fishing fleets is a good signal for how the Magellanic penguins will fare in a given winter as they store nutrition to prepare for the breeding season. There is a small anchovy fishery in the winter, and penguins also favor anchovies. But when the boats don’t do well catching anchovies in the winter, that is bad news for penguins in the following breeding season.
“They do well when the fishermen are catching anchovies. If the fishermen are not successful, the penguins start to falter,” Boersma said. “If the fishery expands and then collapses, as most do, the penguins will be in trouble.
“Penguins are having trouble with food on their wintering grounds and if that happens they’re not going to come back to their breeding grounds,” she said. “If we continue to fish down the food chain and take smaller and smaller fish like anchovies, there won’t be anything left for penguins and other wildlife that depend on these small fish for food.”