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."