ID Help: Gray Dove-Sized, Masked, Hooked Beak, High Pitched Two-Tone Call, Hawkish

by diana
(Security, CO)

Does anyone know what kind of bird this is? It stays high in tree tops and has a piercing high-pitched two-note call. It looks reminiscent of a mini- bald eagle when flying because its head is lighter than its body and the way it flaps its wings, but it is more gray than brown. It seems to have a tiny bit of yellow on its belly and kind of a mask around the eyes. It is about the size of a mourning or collared dove but very different shape. It is a hooked beak like a parrot's. I've been hearing its call all summer in the early morning and various other times and seen a few fly high up as well, but hadn't seen the bird while calling to associate it with the call until today and to get a decent look at it as well.