In theory a human and a chicken have the exact same anatomical base structure. The entire hierarchy can be the same. Chicken has a finger and a toe less, and a tail, but the rest is totalyl reuseable. The reason behind it however and whether it actually benefits your production given such different shapes is a different story. But if you had to animatie the transformation from a chicken to a man, you certainly could (if you make them use the same skeletal hierarchy)