I'm not sure I understand the difficulty believing a sparrowhawk could catch and eat a pigeon. Are we all talking about the same bird?

A quick Google search would seem to support EBarnacle's assertion:
http://www.google.com/#hl=en&expIds=17259,27586,27761,27796,27868,27937&sugexp=leprodsca4&xhr=t&q=Sparrowhawk+devouring+a+pigeon

Cordially,

Maeve