Why do your budgies preen each other?

They preen each other because they have deep affection for one another, or they're just really good friends and want to help each other out by preening " that hard spot".

Budgies must preen their feathers by gathering some oil from the gland at the base of their tail and running it down each feather. They can't preen their own head and cheek feathers. Mutual preening is shared by bonded pairs as well as cage mates.