Is birbie based upon the birds of paradise?

Yes, it is!

More specifically, Birbie is based on the Superb Bird-of-Paradise, Aveden is inspired by Wilson’s bird-of-paradise (mainly the head markings), and Splendifowl is based on the Greater bird-of-paradise.

For some footage of the real life inspirations behind these Pokemon, I recommend this video.

Its very likely that the Alola Pokemon Oricorio, the dancing bird, was inspired by some of these birds as well!