Here's a link to my town's ordinances. I think it is fairly thoughtfully written, with clear definitions and distinctions. Livestock are not allowed on less than 1 acre, but fowl are. They even define what constitutes a "unit" of livestock...
Doncha know, keeping chickens is low-class, dirty and just ain't right. I live in HOA land where people voluntarily let others tell them what garage door to buy, what color to paint their house, where they can park their car, put their satellite dish, how many pets they can have, how to mow...