Marine biologists and veterinarians said the bodies of more than 500 penguins have been washed up on beaches in southern Brazil over the past week.
They told the G1 online news site that the Centre of Coastal and Marine Studies was investigating what caused the deaths of the 512 penguins found on beaches of the southern state of Rio Grande do Sul.
The cause of death should be known in about 30 days.
Biologists at the centre told G1 the penguins were migrating north from Argentina in search of food in warmer waters. They said the birds appeared well-fed, unhurt and without oil stains.