The 49 freed penguins were among the sole survivors of the unexplained spill in May in the straits of Magellan, which separates Tierra del Fuego from the rest of Argentina.

Wildlife and marine officials had no idea a spill had taken place until dead oil-covered penguins started turning up on the rocky beaches of Cape Virgenes, site of the second largest penguin colony in the world.

When a rescue mission was launched, more than 220 were found alive and coated in sticky, black oil.

Several died before they could be rescued but the survivors were airlifted to a marine facility in San Clemente del Tuyu, southeast of Buenos Aires, so workers could begin the painstaking task of restoring their feathers to their former black-and-white, waterproofed glory.

Dozens of tourists turned out to watch as the workers carried the caged penguins down to the wind-swept beach close to the mouth of the River Plate.

As their cages were opened, the birds made a dash for the water, racing past the crowd and into the ocean, disappearing under the waves. Moments later, they could be seen swimming away from the coast before vanishing into the distance.

"This makes it all worthwhile," said Valeria Ruoppolo, a veterinarian with the International Fund for Animal Welfare who helped in the penguin rescue. She was one of the first rescuers to reach the remote area after the initial discovery of nearly 100 dead penguins at Cape Virgenes, where up to 400,000 penguins nest in the warmer months.

Ms Ruoppolo said they had initially tried to rehabilitate the surviving penguins at the site but that their efforts were hampered by freezing temperatures. A decision was then taken to airlift the birds to warmer climes to speed up the cleaning and recovery process.

Covered in oil, penguins cannot tolerate the cold waters of the southern Atlantic and will not dive for food in the still-colder deep waters, putting them at risk of starvation. The process of cleaning their feathers is a lengthy one, requiring repeated washing and drying to restore the waterproofing.

"They need to get wet and dry off many times," Ms. Ruoppolo said."This is how they align their feathers to the normal position, so the feathers interlock together and form a barrier against the cold water."

How the penguins came to be covered in oil remains a mystery. Coast guards sent surveillance flights over the area but were never able to trace the source of the spill.

Rescuers believe it was most likely to be a ship dumping engine oil at sea."Having all these ships throwing their oil in the water causes a big problem," Ms Ruoppolo said. Penguins are particularly vulnerable to such spills because of their wide-ranging migratory routes.

Hundreds were found dead from this spill but officials said they would never know the real toll. Thousands, however, probably survived because they had already migrated from the area to warmer climes as the southern hemisphere winter set in.

Further north, in Brazil, another penguin rescue mission was underway when the air force and navy announced a join operation to repatriate penguins stranded on the beaches of Rio to their homes in the Antartic. More than 100 birds will be taken home by plane and ship in a trip scheduled for later this month.

Scores of penguins wash up on Brazilian beaches each winter after floating for thousands of miles on Antarctic ice floes that drift off and melt in warmer waters. Once in Brazil, the flightless birds are stuck. But this year’s exiles are luckier than their predecessors, who have usually ended up in the zoo.

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