Veterinarians are investigating after 512 dead penguins washed up on Brazilian beaches in the state of Rio Grande do Sul on Friday.
The animals landed near the towns of Tramandai and Cidreira, Agence France-Presse reported.
The Center of Coastal and Marine Studies (Ceclimar) took tissue samples to Porto Alegre University in an attempt to determine cause of death, AFP said.
It may take as long as 30 days for any answers.
About a week ago, BBC reported penguins near Rio became a tourist attraction after surfacing near the tropical beaches there.
Rescuers pulled the sickly birds from the water and nursed them back to health.
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Jeferson Pires, who is helping rehabilitate the birds, said they have stomach ulcers from going long periods without food.
It’s common for younger birds to lose their ways searching for food, BBC said.
The birds migrate annually from Argentina to Brazil, but ocean currents can carry them off course.
“After rehab, we are working on the logistics plan to take them back to a rehab center … in order to release these animals afterwards back in nature, in their natural habitat,” Silvia Torres, an animal welfare worker, told BBC.
This week’s incident is different, however, because the penguins appeared healthy, well fed and free of oil, The Associated Press said.
The Magellenic penguins live near southern Argentina and Chile.
They migrate from March to September to Sao Paulo.
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