Andy, I think you'll find that this is an immature Black-crowned Night Heron. Bitterns rarely if ever sit in trees and the white spots on the back are diagnostic, a Bittern would be plainer on the back.This little guy is always hiding in the same trees alongside the lake where we live. I can easily walk up to within 10 feet of him without scaring him off. I believe it's a Bittern. (I'm not a "bird man").