More than 400 penguins, most of them young, have been found dead on the beaches of Rio de Janeiro state over the past two months, according to Eduardo Pimenta, superintendent for the state coastal protection and environment agency in the resort city of Cabo Frio.
While it is common here to find some penguins - both dead and alive - swept by strong ocean currents from the Strait of Magellan, Pimenta said there have been more this year than at any time in recent memory.
Experts are divided over the possible causes.
Thiago Muniz, a veterinarian at the Niteroi Zoo, said he believed overfishing has forced the penguins to swim further from shore to find fish to eat "and that leaves them more vulnerable to getting caught up in the strong ocean currents."
Niteroi, the state's biggest zoo, already has already received about 100 penguins for treatment this year and many are drenched in petroleum, Muniz said. The Campos oil field that supplies most of Brazil's oil lies offshore.
Muniz said he hadn't seen penguins suffering from the effects of other pollutants, but he pointed out that already dead penguins aren't brought in for treatment.
Pimenta suggested pollution is to blame.
"Aside from the oil in the Campos basin, the pollution is lowering the animals' immunity, leaving them vulnerable to funguses and bacteria that attack their lungs," Pimenta said, quoting biologists who work with him.
But biologist Erli Costa of Rio de Janeiro's Federal University suggested weather patterns could be involved.
"I don't think the levels of pollution are high enough to affect the birds so quickly. I think instead we're seeing more young and sick penguins because of global warming, which affects ocean currents and creates more cyclones, making the seas rougher," Costa said.
Costa said the vast majority of penguins turning up are baby birds that have just left the nest and are unable to out-swim the strong ocean currents they encounter while searching for food.
Every year, Brazil airlifts dozens of penguins back to Antarctica or Patagonia.