It's Rats Vs. Penguins on Contested Chilean Island A 3-week-old Humboldt Penguin gazes plaintively from the opening of its nest, waiting for its parents to return with food. They may be out hunting for fish. But if they take much longer, they might not have a chick to provide for. Invading rats with bodies up to 8 inches (20 centimeters) long have begun eating eggs and chicks, and some experts fear that unless the rats are eradicated, they could tip the Humboldt penguin toward extinction. These penguins with distinctive black bands across their chests also are threatened by changing sea currents, fierce gulls and nesting pelicans whose relatively heavy bodies collapse their shallow earthen caves. And the biggest peril has been the nets of fishing boats that trap and suffocate the adults, at least until now. "The cause of the decline in the penguin population is man," said bird veterinarian Paula Arce. And of its eggs ... That could be the rats. The Humboldt population has dropped from hundreds of thousands decades ago to below 45,000, said Alejandro Simeone, who directs the Ecology and Biodiversity Department at Andres Bello University in Santiago, Chile's capital. The International Union for the Conservation of Nature has had the penguins on its vulnerable list since 1988. In this photo taken July 7, 2012, a recently born Humboldt penguin lies in a nest on Pajaro Nino Island, Chile. A rat invasion is threatening to tip Humboldt penguins toward extinction. Their eggs have become a favored rat dish, and rats also have been seen eating recently born penguin chicks when their parents were away. (AP Photo/Eva Vergara) Close Humboldt penguins nest only on several dozen coastal islands scattered along more than 1,000 miles (kilometers) of the Chilean and Peruvian coastline. They traditionally forage close by their homes, often mate for life and reproduce twice a year, a pair of eggs at a time. Hatchlings weigh as little as 2.3 ounces (65 grams) and are covered in a soft, grey down. They are utterly dependent on their parents for 10 perilous weeks until they can feed themselves at sea. The father and mother take turns sitting on them while the other ventures into the ocean for food, usually never leaving the little ones alone. But they depend on the frigid Humboldt current to deliver sardines and other tasty fish from Antarctica, and the current has moved farther off the coast in recent years. Foraging now requires longer journeys, exposing their hatchlings to predators. The Zoological Society of Milwaukee and the county zoo it sponsors, which includes a small Humboldt penguin exhibit, has spent more than $200,000 researching the birds' plight over the years, paying for annual population surveys and providing small stipends to Chilean researchers to make regular visits to the breeding grounds. That money also supported research published in the March Journal of Ornithology that suggested rats could be devouring penguin eggs at a devastating rate. Simeone and bird veterinarians Arce and Maximiliano Daigre put boiled chicken eggs in empty penguin nests at Islote Pajaro Nino and discovered that 50 percent were quickly eaten by Norway Rats, while gulls, a more traditional predator, took just 16 percent. The experiment was repeated on another coastal Chilean island, where Black Rats had destroyed 70 percent just 12 hours later. Simeone said some of the rats that reach Islote Pajaro Nino, or "Bird Child Island," come from the Algarrobo resort on Chile's coast, where millionaire residents keep yachts in a sheltered harbor and spend their summers surrounded by elegant flowered gardens.