A few questions come to mind. What happens to the waste that comes out of the chickens? Does this waste (and the smell and the sound) impose externalities on neighbors? What happens to the hens who have reached the end of their egg-laying life? What happens to the hens who, whoops, turn out to be roosters. Bird flu? Will the chickens be protected from preditors and extreme weather conditions? How much does it cost to maintain the chickens and how expensive is supplemental feed and veterinary care?
I'm not necessarily trying to discourage backyard chickens. I just want to know why taxpayer A should be required to pay for person B's chickens? If the problem is food waste, and supposing it causes some unmentioned externalities, why not just increase the price of garbage pick-up? Then households can respond in whatever ways they find most effective and convenient. I doubt, for most, that chickens are the optimal solution.