Update: I saw the Sparrowhawk 4 times again yesterday. A very large female bird with dark brown plumage. She returned to the place below my kitchen window searching in vain for the kill she made the day before. Scared every other bird away from the garden. My previous dilemma was should I leave the gory pigeon corpse lying there, or dispose of it? If I left it that would attract the Sparrowhawk anyway, but it might mean no need for another kill, at least for a day. A life saved, perhaps. Or, the fox or a cat would eat it overnight. Who knows.