First of all, you could make them a little bigger, it makes it easier to work with, but isn't needed. Also, they need more contrast, especially the Cardinal, as I can't see any thing but a basic shape of the bird, I can't see the wing shape or the eye. The Pigeon needs a head remake, as it is looking like you just cut it off you another bird and put it on, Pigeons barley have a neck, it is just a curve from the tail to the top of the head, your Pigeon looks more like a duck. For the Seagull (Ar these supposed to be capitalized?) You could use a little brigher gray, and minimize the shadow at the top of the head, as there is nothing to cast a big shadow there.