Vent pecking

Vent pecking (or cloacal cannibalism):

Pecking at the vent or cloaca of another bird is one of the most severe forms of cannibalistic behaviour in laying hens. It can lead to the death of the bird that is pecked and to high mortality levels in the flock as a whole. It is most often seen between the time when the birds start to lay eggs and the time of peak egg production.

For this reason it is thought to be related in some way to the egg-laying process, perhaps to hormonal changes associated with egg production. It is more prevalent in certain strains of bird and in certain housing systems.

Severe and chronic vent pecking. Photo: Jan Svedberg