What bird can't fly or run very fast, and is different shades of brown, all at the same time?
If you're a man, stand on top of a tree, look down, put the two things you see together, and you might just think maybe the answer has to do with a part of you.
Hints (from the comments below):
American. It's just a word but it's a part of the answer. I think that part might be hard to guess because the riddle doesn't have any clues to that part. The rest of the answer has a clue in the riddle.
Multiple shades of brown all at once could mean a variety of different kinds of brown feathers on one bird.