Hundreds of penguins have been washed up dead on the beaches of Brazil southern state of Sao Paulo.
Scientists are still investigating what could have caused the death of around 530 penguins, other sea birds, dolphins and three giant turtles found on the shores of coastal towns of Peruibe, Praia Grande and Itanhaem.
They say autopsies carried out on some of the penguin carcasses suggest they could have starved to death, as their stomachs were completely empty. They are now trying to establish if strong currents and colder temperatures may be to blame.
Thiago do Nascimento of the Peruibe Aquarium says the cooler than usual temperatures off the coast could have driven away the fish and squid the penguins feed on.
But he did not rule out that over-fishing could have decimated the penguins' food sources.
Penguins migrate from the south of Argentina and Chile along the South American continent to the Brazilian coast.
Mr Nascimento said between 100 and 150 penguins showed up on the beaches every year, but that they were normally alive, with only around 10 washed up dead in an average year.
What worries us this year is the absurdly high number of penguins that have appeared dead in a short period of time, he told the Associated Press news agency.
The Praia Grande authorities have ruled out pollution as the cause.