Hi AllyI used to work at Downsview, over the course of many years observed all the birds of prey you posted.Kestrels are there year round and actually breed in multiple locations at the Bombardier site. Northern Harrier's are usually spring and winter migrants.If you are there early in the morning during winter you might also spot a Snowy flying over the base. Short Eared Owls are also common in the evening and morning near the airfield.Nice pic'sNapper