Fat-bird watching

Extra: crows on the beach.
Or are they rooks?
The RSPB say that crows "are fairly solitary, usually found alone or in pairs"
while rooks are "very sociable birds, and you're not likely to see one on its own"
So are they crows or rooks?
or crooks?
Plus, if crows are so solitary and rooks so sociable, why are there eight collective nouns for crows but only three for rooks?

More though Flickr is playing up today