Why kill 'em? If you're going to take the trouble to trap them alive, then why don't you just set 'em free out in the country? All this talk of drowning and asphyxiation via carbon monoxide seems kinda barbaric when more humane options exist.
I agree. Also when they kill them new ones will just migrate in when there is a vacancy. There's too many out there for one person to make any difference at all, except to satisfy their anger, at the cost of suffering for a small creature.
I could never kill them like that. Watching a small life struggling for air for so long is barbaric.