here's a conclusion to the original post:
dropped my wife off at work today, which is the Humber Campus. I went to the arboretum to take a stroll.
there are clear signs of owlS (more than 1) where the OP saw the LEO. but....there wasn't an owl to be seen. i talked to the staff and its been around 10 days since one was last spotted. they assume that all 3 owls migrated south.
so if you're a fan of whitewash and owl pellets, there's still lots to be seen.
but the arboretum's a great place to see birds. there's a resident RTH that perches near the bird feeders, and lots of robins, chickadees, house finches, goldfinches, nutchatches and downy woodpeckers to be seen.