Crows are far from Thick, They say they are one of The most intelligent of the lot.
If a Pigeon decides it wants to feed on a particular field, then it will come in no matter what. A Crow errs on the side of caution
As for the easiest to shoot..
Pest Species I would say the lumbering Jay flitting between the branches.
Game Species, Mallard coming into a flightpond I find easiest, the Pheasant, Partridge and others are all different, but some Pheasants are very easy.
Regards
SS
crows are smart to a point... i've seen them use military like tactics when checking out