Cute cats, Philip, I'm surprised you get any birds in your garden! But if they like to watch but not hunt...
Melanie, you're right - a group of crows is indeed a 'murder'. But I believe that Philip's birds are in fact jackdaws (same family, but smaller than crows, and the only ones in the group with pale eyes). A group of jackdaws is a 'clattering'!
But what do you call a group of egrets (I think!) on the backs of hippos?