Allopreening

Mutual preening between two birds, the main purpose of which is to reduce the instinctive aggression when birds are in close contact. In the breeding season allopreening helps to strengthen the pair bond between the male and female.

Jungle Babblers 

This behaviour is especially common in parrots, babblers, crows and some finches, or when a bird preens the feathers of another, usually its mate is also called “mutual preening” .