I wonder if they are what have been holding up bows and arrows? I believe you have to have feathers to make proper arrows. As I've seen no other birds in the game (not even turkeys though at times I could have sworn I'd met a few) I expect it's all the chicken's fault.
What do you all think?
Also, I vote for mutant chickens (mutant livestock is mentioned as a good idea in the FAQ) or better yet mutant rabbits, what's your preference for mutants?