The Birds of North America account clearly documents the Snowy Owl
feeding on birds, citing birds from songbirds to medium sized geese are
taken. I recall an account of a Snowy Owl killing and feeding on a
Great Blue Heron. In one study, 80% of the diet was waterfowl with
grebes being among the most heavily preyed upon species.
I would say a pigeon would be an easy prey given this.