First of all, I love this! I am an angry birds addict, and you did a great job depicting the bird!
However, if you're looking for tips, I'd suggest a thicker fabric, or thinner yarn.
I don't know much about crayon tinting, but something about the way it mixes with the yard needs a little something extra. I'd probably do a little more than just the black outline with the yarn. Maybe add a few red feathers with it. The crayon is so smooth, and the black is so chunky and textured, that the two seem like they are fighting with each other. Maybe if there were more colors of yarn that matched the crayon, it would seem more intentional.
Man, that bird is so angry.
I would love to see him flying out of the slingshot!