BERLIN (AP) — German police say a Humboldt penguin has been stolen out of its cage from a zoo in the southwestern city of Mannheim, and zookeepers say the bird could easily die if it’s not returned soon.

Zookeepers noticed the penguin missing during a routine count Saturday of the South American birds, the dpa news agency reported Monday.

After a search of the grounds, zoo personnel were unable to find any signs that the flight-less penguin, which is 50 centimeters (20 inches) tall and weighs 5 kilograms (11 pounds), escaped. They concluded it was stolen.

The bird has a number 53 on its wing and an implanted chip to identify it.

Zookeepers are pleading for the return of the bird, saying that without its special diet and controlled environment it will not survive.