My favorite cartoon ravens:
Your Raven sketches are really really good, I don't know if there's any constructive criticism I could give about them. The proportions all seem fairly accurate to me. Actually I think the head might be a little too wide on some of them but it could just be the perspective
I would be interested to see you post one that's fully fleshed out, maybe it would be easier to give good criticism at that point.
I usually seem to do... adequately on sketch; although I usually find somethings that makes me cringe. Biggest problem of me so far has been my inability to convert any of my sketch into a line-work that I can be happy with.
I've tried doing a rendering and the lack of formal education in art really isn't helping me currently. I've started doing my own private education to figure out how to properly do a rendering and then MLP actually introduced me to the world of vectors. I'm currently teaching myself on doing digital painting while learning how to use illustrator. I would like to be proficient with both of them in near future.