Rio de Janeiro, Brazil (CNN) -- Located only 16 kilometers from Rio de Janeiro, Niteroi Zoo is home to dozens of animal species from this tropical region of Brazil. But lately the zoo has gained more recognition for its work in rescuing animals and returning them to their natural habitat than for its size or animal variety.
In the past few years, the zoo has rescued more than 1,000 Magellan penguins, returning them to their natural habitat with the help of the Brazilian Air Force.
On a recent visit to Niteroi, the zoo's president Giselda D'Amelio Condiotto shows us three of their most recent guests, three Magellan penguins who are being treated at her facility. The penguins seem to have an insatiable appetite. They eat about two kilograms of fish in less than a minute... and that's just lunch.
Among the zoo staff they're known as Romario, Cristiano, and Jose Miguel. They were named after Brazilian football stars.
"These last penguins arrived in December," Condiotto says. "They were brought by a tuna fisherman who owns a ship and rescued them from the sea."
Amazingly, Magellan penguins are also surfacing at the world-famous beaches of Ipanema and Copacabana in Rio de Janeiro located thousands of kilometers north of their natural habitat in Patagonia or Antarctica. Condiotto says the penguins started showing up for no apparent reason.
"In 1999 I started to receive penguins. It was something like two or three per year. Then it started to grow gradually. In 2004 we got 100 penguins. Then in 2008 there was a big, ecological imbalance, and almost 700 penguins arrived here," she told CNN.
It's normal for Magellan penguins to leave their colonies in the Antarctic in an annual migration in search of fish, following the plankton-rich, frigid water currents traveling north along the coasts of South America. What has changed is that they are increasingly unable to return home because they get sick, weak, or disoriented for reasons that have yet to be determined.
David Alves Dias is a beach vendor who works at the Ipanema Beach. He says that last winter, as he was getting ready to being his day, he noticed some tiny creatures walking on the beach. At first he didn't know what they were; but as he walked in their direction, he realized they were penguins.
"People were so surprised when they saw the penguins in Ipanema Beach," Dias said. The Rio native says that he had never seen penguins there: "Probably it's a change in the water, you know?"
Dan Bahr is another Rio resident who enjoys jogging by the beach every afternoon points out the obvious: people just don't expect to see penguins in a tropical beach.
"Absolutely not! Sometimes they just walk up here and people surround them and then we call the fire brigade," Bahr said. After picking up the penguins at the beach, firefighters take them to Niteroi Zoo where they know they can be helped.
The penguins that end up at Niteroi Zoo are only part of the story. Authorities are finding hundreds of dead penguins on the beaches of Rio and it's impossible to determine how many more die in the ocean. Brazil's environmental protection agency, IBAMA, is taking a close look at the problem.
Environmental analyst Maria de Souza believes pollution of the ocean is causing the penguins to get sick and become disoriented. "Animals that swim in oil fields come here with petroleum on their bodies. They get contaminated; you have to wash the animal to get rid of the pollution," said de Souza .
Other scientists believe that overfishing is disrupting the penguins' natural food chain, forcing them to swim longer distances to find fish. Yet another theory points to global warming which could be disrupting ocean currents that penguins used to rely on to swim back and forth.
After being fed and treated at the Niteroi Zoo, the Brazilian Air Force returns some penguins to their natural habitat. But Romario, Cristiano, and Jose Miguel have become so used to humans that scientists believe they can no longer survive on their own.