The true story of the 'Birdman of Alcatraz' is about Robert Stroud. He was serving time in prison. He developed an interest in birds, especially canaries. He studied them intensively, even breeding them in his cell. This made him stand out among the prisoners. But don't forget, he was in prison for murder. His story got a lot of attention because it was so unusual. People were intrigued by how he could turn his life in prison into something more positive, at least in the area of bird study.
Definitely. The movie takes elements from the actual experiences of Robert Stroud, although some artistic liberties might have been taken for cinematic purposes.