I figured out what kind of owl was living behind our house by comparing its hoots to online recordings. I'm pretty sure we've got one of these:
A Great Horned Owl (Bubo Virginianus), indigenous to the whole of North America. According to the Reader's Digest Book of Birds, this guy is basically a monster.
"Once described as 'the tiger of the woods'...it is equipped with powerful talons and a sharp hooked beak for tearing flesh from its kill. And thus arrayed, it seems to know no fear. Squirrels, Rabbits, skunks, songbirds, geese, hawks, even porcupines are all fair game for satisfying the horned owls enormous appetite...The ground beneath the roost is characteristically littered with bones, feathers, and other leftovers from the feast."
The emphasis on porcupines was my own. I find that unbelievable and ridiculous! That's a 12-35lb animal coated in razor sharp quills. Amazing.
The book goes on to mention that very occasionally, these guys swoop down on ladies in fur hats because the mistake the pelt for living prey. I hope I don't get swooped!