Why do crows exist? Every morning I throw seeds out for the birds and say to him if a big group of crows come for him to shoo them away. Hence his question. And I for one have no answer. The reason I ask him to do this by the way is that those seeds will feed the smaller birds for hours but the crows finish everything in 10 minutes leaving nothing for anyone else.
at four he is looking for a simple answer such as
God created them for us to feed, but others as well
or
because they are birds like any other
a darwinian answer - they fill an ecological gap in the UK which would be filled by something else on another continent if crows werent there
is NOT required
And teach him that if there is a crowd of them then they are either rooks or jackdaws, not crows. Crows are carrion feeders, rooks eat seeds (and other things to).
The 1 rook's a crow etc only works in the breeding season. I've seen over a 100 crows feeding together in my local park. They were scoffing a loaf of sliced bread that someone had left by a bench.