I was curious so-o-o-o-o ... from Birds of North America ...
"extraordinary vision in locating and catching prey"
On the menu:
Lemmings
Ptarmigan
Rabbits
Rats, voles and mice
Waders
Passerines
Ancient Murrelets other alcids
Ducks (esp. Horned Grebe)
I assume they might eat Prairie Dogs??
Thanks Gary Lefko, Nunn
http://coloradobirder.ning.com/