I saw a Kestrel eating a mouse in the exact area you describe (James Gardens) Saturday as well. Kind of a smallish Kestrel. A short stroll down into Lambton Woods produced numerous White-breasted Nuthatches, Downys, Hairys, House Finches, Common Goldeneyes, Common Mergansers. Was hoping to see a Red-bellied Woodpecker. No luck. My first visit there. Very nice spot.