Allopreening is a behavior often seen in a mated pair of birds (allogrooming also occurs in mammal species most notably primates). Allopreening is the mutual preening of another birds feathers. Sometimes the preening will switch back and forth from bird to bird. This behavior can be performed to enhance feather maintenance (keeping feathers clean of parasites) or to strengthen social bonds. The receiver of the preening will often lower their head, fluff out their feathers and in general have an 'Awwmygawh that feels good' look on their face. Birds attached to humans will also preen their humans, either trying to preen their hair, beard, moustache, eyebrows...eyelashes... It's one of the most adorable bird behaviors I've ever seen (well, with the exception of a parrot trying to preen your eyelashes, that might hurt).
So here is a feature of birds being adorable with each other!