The Birdman was about as "calm and friendly" as Hannibal Lector in Silence of the Lambs. In other words, he was actually vicious.
This movie completely misleads the audience to think the Birdman was an innocent man wrongly convicted. And for that, it deserves just 2 stars.
Going in blind and taking it at face value, Birdman of Alcatraz is a wonderful movie. I rate it a solid 8.
There's no doubt Stroud became an authority on birds. However, knowing about Stroud and Alcatraz through books and documentaries, it's really stretching artistic license to the limit.
This may not be the best comparison, but I wouldn't advise on making a movie about Charles Manson depicting him as sympathetic and misunderstood.