Anything avian is related to birds. Avian flu is a bird flu that can be transmitted to humans. An aviator is someone who flies a plane, which may help you recall that avian things are related to birds. Feathers are a feature of avian anatomy. Bird-watchers are avian experts who can identify birds apart. Ornithologists are also avian experts: they are the professionals associated with the study of birds.
Synonym: Bird-like, Birdly, Aerial