More than 200 oil-slicked penguins have washed up dead on the beaches of a popular Brazilian resort, and officials say they are searching for a cause.

Authorities said they have counted nearly 200 dead penguins found on the beaches of the island city of Florianopolis, but people bringing in live penguins covered with oil reported seeing hundreds more dead on the beaches, said Manuela Osorio, a veterinarian with a group caring for the surviving birds.

"We don't know for sure because nobody is keeping tabs of the dead," she said. "What we do know is we have 155 live penguins we are treating for oil intoxication."

Marcelo Duarte of the Santa Catarina state environmental police said nearly 200 washed up since Sunday, and told the Associated Press that the oil probably leaked from a large ship and police say they are trying to determine the culprit.

While it is common in Brazil to find some penguins — both dead and alive — swept by strong ocean currents from the Strait of Magellan — the birds are showing up in greater numbers than most experts can remember.

They also are heading much farther north, with reports of penguins washing up as far away as Rio Grande do Norte state, near the equator.

Some biologists believe stronger-than-usual ocean currents or colder-than-usual ocean temperatures have pulled the birds north. Others suggest overfishing near Patagonia and Antarctica has forced the penguins to swim farther in search of food.