Penguins from the largest colony on mainland South America are being forced to swim the equivalent of two marathons farther to find food because of the effects of climate change.
The survival of the Magellanic penguin colony at Punta Tombo, on the Atlantic coast of Argentina, is being threatened by the increasing distances the birds must travel to feed themselves and their chicks, research has shown.
Dee Boersma, of the University of Washington in Seattle, said that Punta Tombo penguins were now routinely swimming 25 miles farther on their foraging expeditions than they did 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.
The longer foraging trips have contributed to the colony's decline: penguin numbers have fallen by more than 20 per cent in the past 22 years, leaving only 200,000 breeding pairs today.
One of the main reasons for the penguins' marathon swim is global warming, which has led to great variation in the region's climate. This variation means that penguins are nesting in areas that are close to food one year but much farther away in others. It also alters ocean currents, which move fish stocks farther away from the colony in some years.
Some penguins that Professor Boersma originally tagged in Punta Tombo are also turning up in colonies as far as 250 miles farther north, because they have migrated in search of food. Although these birds regularly find new colonies, they are generally outside protected reserves such as Punta Tombo, and so are at greater risk.
Oil pollution and overfishing are also having a significant effect on penguin feeding patterns. Details of the research were presented yesterday at the American Association for the Advancement of Science conference in Chicago.
During the breeding season, each member of a pair will take turns to incubate the eggs or guard the chicks, while the other goes foraging for days or even weeks at a time. On its return, a parent will regurgitate food for its partner and its young.
Longer foraging swims reduce the chances of a penguin pair successfully hatching and raising their chicks.
Breeding success is also being compromised by increasingly frequent floods caused by heavy rain. The Punta Tomba reserve has recorded 2in (6.4cm) of rain five times in the past 25 years between mid-October and mid-December, a key period for the survival of eggs and chicks.
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Professor Boersma said: "That turns their little nests into swimming pools." She said that the success of Argentine anchovy fishing fleets was often a good marker for whether Magellanic penguins would be able to survive the winter and breed afterwards. "They do well when the fishermen are catching anchovies. If the fishermen are not successful, the penguins start to falter. 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. 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."
The Magellanic penguin, Spheniscus magellanicus, is named after the 16th-century explorer who led the first circumnavigation of the world. It is classed as near-threatened on the Red List of endangered species.
Many other penguin species were also under threat, Professor Boersma said. "Of the 17 species of penguins 12 are rapidly declining and their distribution and abundance is shifting as well. Increasing human perturbations from climate change, petroleum pollution, fisheries, and tourism are political problems not easy to manage."
Going the distance
- European eels swim 3,000 miles (4,830km) across the Atlantic Ocean to reproduce in the Sargasso Sea, living off reserves of fat. After spawning they die, and ocean currents carry their offspring back towards the coasts of Europe
- The shrinking Arctic ice shelf means that polar bears have had to swim 60 miles to find food
- Alaskan salmon swim upstream in their thousands from July to September to spawn, turning rivers into a mass of seething fish on the longest salmon run in the world. Some chum salmon swim more than 2,000 miles of the Yukon River
- Susie Maroney, below, a record-breaking Australian distance swimmer, swam from Mexico to Cuba in 1998 across 122 miles of open sea in 38 hours, 33 minutes
Sources: University of Texas Marine Science Institute; Alaska, by Jim DuFresne and Aaron Spitzer; Times archives