If you intend on erecting the nest box in your backyard...
Being that you live near the Don Valley system, where there are probably all kinds of owls to be discovered, I would say that building a nest box and trying to get an owl that would normally nest in the valley or other nearby park to come and live in is probably not such a great idea...they're far better off where they are, away from the hustle and bustle of us humans.
One late night last spring as I sat in a friend's car outside my house chatting, we watched as a family of raccoons crossed the street halfway up the block. As the two young ones were almost to the curb, a Great Horned Owl swooped down at them from the dark sky above (pretty amazing to see nature at it's best!) The problem was though that we saw all of this through the headlights of a car that was speeding along the street (the driver probably figured that the young were far enough across the road and it was safe to pass). The taillights went on and the driver swerved when the big owl flew down from above just out in front of him. The owl was unsuccessful as it was probably startled by the car in as much as the driver was startled by the owl. A very close call.
Over the years, I've seen a few Great Horned Owls in the neighbourhood, not sure if they live in the trees in the immediate area or that they are coming up from the Scarborough Bluffs (only a couple of block to the south) in search of food.
Walter
