There are 4 or 5 'feral' cats around us and they seem to do a good job
on local vermin, including the odd pigeon, though twice I've witnessed a
hawk down a wood pigeon into the back garden. Strangely he seemed very
wary of 3 or 4 magpies who materialised within a few minutes and stalked
around him and his kill until he took off.

Going OT, however, you'll find that many birds will gang up on birds of prey
to get them out of the area before they have to roost. My parents were
involved for some time with the care of Owls (please don't get going on the
ethics of captive animals), however, one escaped and being a captive-breed
was unable to fend for itself, and was harassed from place to place by the
local bird population, from sparrows to crows.

I also have vague memories as a child of some BoP bringing its quarry down
in the back garden - the only reason we knew of that was the din from all
the birds who materialised on the scene. Just goes to show that its a
dog-eat-dog (or bird-eat-bird) world out there.

Mike