Nom, nom, nom

You'd think that zoo keepers would be a little bit better informed about the risks that they face from the animals in their charge really. But apparently not:

The director of the Berlin Zoo made famous by the polar bear cub Knut has had his finger bitten off by a chimpanzee called Pedro.

Bernhard Blaszkiewitz, 55, was feeding Pedro walnuts as he showed a visitor round the zoo Monday when the ape grabbed his hand and bit off his right index finger.

The reason for the biting was not that the chimp was hungry though. It was a display of dominance. As the leader of the group Pedro has to keep making sure that people know he's the leader of the group, thus the "nom, nom" incident.

That's the explanation at least. However, biting off fingers as dominance gestures. How common is this? How many other chimps out there missing digits are there?