Nature & Wildlife - 47 free documentaries about birds.
Start with David Attenborough Presents: Hummingbirds - Jewelled Messengers (53 min, Free Documentary), then David Attenborough (53 min, Real Wild). All 47 documentaries here are free to watch from their makers' official uploads. To read deeper, the top-rated book on birds is The Genius of Birds by Jennifer Ackerman.