Marine biologists in Brazil have launched an investigation after hundreds of dead penguins washed ashore in the southern state of Rio Grande do Sul, they said Monday.
More than 500 birds have been found on beaches over the past week, and that figure has steadily risen over the past few days, according to experts from Brazil's Center of Coastal and Marine Studies (Ceclimar).
Japan's fugitive penguin captured
The figure has been especially puzzling for the marine scientists, who say the birds are badly decomposed but otherwise seem unhurt and without oil stains.
The discovery follows an official inquiry launched by the Peruvian government this year when close to 3,000 dolphins and more than 500 pelicans washed up along the country's northern coast.
Mauricio Tazeres, a biologist from the Center of Coastal and Marine Studies, said "it's actually pretty common for us to find at least some penguins but never in this number.
Stolen penguin back safe at Sea World
"The animals usually migrate from Argentina around this time of year in search of food and warmer weather, and each year, some do wash up. But over 500 is a very, very high number, and right now, I simply do not have an explanation.
"We have collected some samples for autopsy, but the animals are so decomposed, it is going to make analysis very difficult," he said. "The animals were a lot smaller in terms of size and weight than normal penguins, so we think it will be natural causes, but it is certainly very strange."