Please help me identify this silhouette of a bird

[Nico Toutenhoofd]

I was up near Gold Hill, Colorado, on an early morning bike ride and I got this photo of a big bird taking of from a tree. I'd love to know what it might be - I'm assuming it's a hawk or an eagle:

https://www.dropbox.com/s/5o6aogqhwaumjud/Screenshot%202015-08-14%2015.24.06.png?dl=0

As a silhouette it's a bit hard to tell, I know.

Thanks!
Nico