The best way to determine if he has parasites is to lift the feathers up so you can see then skin. The places where they hide the most are under the chin, under the wings, belly, around the vent and between their legs. When you lift their feathers up you will more than likely see bugs scurry out of sight or see eggs from the bugs. Here are some photos to help you out.
type of louse to look for on a pigeon
flea
Pigeon lice
lice eggs on feathers (always found at the base of the feather)
lice eggs on feathers