Brazil is staging a military operation involving a Hercules transport plane and Navy ships — all to return four dozen wayward penguins to the icy waters of Antarctica, authorities said Wednesday.

The 50 birds are the survivors among 135 that started appearing in Rio de Janeiro in early June, dragged to warm Brazilian waters by ocean currents, said Giselda Candiotto, president of Rio's Niteroi Zoo Foundation, which is caring for the penguins.

A Hercules C-130 transport airplane will take the flightless birds to Pelotas in southern Brazil on Sept. 23 for the first leg of their journey home, the Air Force's press office said.

There, they will be examined by veterinarians at the Marine Animal Rehabilitation Center of the Eliezer de Carvalho Rios Oceanographic Museum.

From Pelotas, the penguins will be driven to the coast and placed on Navy ships. They will be taken 40 miles offshore before being released into the southern Atlantic.

"Ocean currents will hopefully carry them back to their natural habitat," Candiotto said. "If everything goes smoothly, the penguins should be back in Antarctica within 10 days after leaving Rio."

Every year between June and August, large numbers of penguins arrive in Rio from the Strait of Magellan, Candiotto said by telephone from Rio.

"They are young, inexperienced animals that, in their search for food, get caught in the ocean currents," she said.

The birds arrive near Rio extremely debilitated and having lost about two-thirds of their normal body weight. About half die of hyperthermia, hyperglycemia and exhaustion, she added.

Brazil began penguin airlifts in 2000, returning as many as 100 a year to their natural habitat, said Lauro Barcellos of the Oceanographic Museum.