Why are penguins dying on the beaches of Brazil?

NITERÓI, Brazil — The discovery of hundreds of young penguins washing up along the Brazilian shoreline over the past month has sparked a scientific mystery over what may have led the birds thousands of miles astray.

The so-called Magellanic penguins began appearing in late June. Many of them dead or barely alive, they arrived on beaches all over southeastern Brazil, about 2,500 miles from their native southern Patagonia. Some of the penguins have since been spotted as far north as the warm-water beaches of the Brazilian state of Bahia, another 600 miles up the Atlantic coast.

Although the penguins regularly migrate up to southern Brazil in search of food, the sheer quantity of penguins washing up farther away than normal has prompted worries that human activity may be throwing off the animals' migratory cycle.

"The penguin population is intimately linked to their supplies of food, so this suggests something is happening to the population of fish they eat," said biologist Marcelo Bertellotti at the National Patagonic Center in Puerto Madryn, Argentina.

"It appears the penguins are not finding fish where they normally do, and one reason could be that warming waters and climate change have impacted the fish population."

No one has yet conducted a formal study of the phenomenon, but Brazilian scientists also blamed human activity for throwing off the penguins' migration.

Some said a recent oil spill off the coast of Uruguay might have wiped out fish populations there, forcing the penguins to search farther north for food. Others suggested that melting ice in Antarctica had strengthened the northbound Malvinas ocean current this year, trapping younger, more vulnerable penguins.

Whatever the reason, dozens of young penguins continued washing up along the Rio de Janeiro state coast this week, sending wildlife officials on a race to rescue the birds.

They found some covered in petroleum, which had exposed them to hypothermia because the contamination eats away the natural body oils that keep penguins waterproof and warm.

About half of the rescued penguins died by the time firefighters transported them to the state's main rehabilitation center, the zoo in the southeastern Brazilian city of Niterói, which has handled about 170 penguins over the past month.

"We find lots of penguins here with catfish bones in them, which they normally don't eat," said Niterói zoo's veterinarian Thiago Muniz. "That suggests they're not finding their normal fish."

Saltwater catfish have a lower fat content than the cold-water fish penguins normally consume, meaning the penguins were getting less thermal protection.

Scientists say human development and global warming have already dramatically altered the frozen Patagonian landscape. Nonetheless, hundreds of thousands of Magellanic penguins have survived and flourish in the region.

That's under threat, however, as oil production and other economic activity invade the penguins' habitat.

"The penguins are dealing with fishing nets and oil spills and all kinds of problems," said Lauro Barcellos, director of an oceanography museum in Porto Alegre, southern Brazil.

Bertellotti of the National Patagonic Center said, however, that the fishing industry in Patagonia has yet to seriously affect penguins because the birds normally eat anchovies, other small fish and squid near the ocean surface, as opposed to the deep-water fish sought by commercial fisheries.