Our city had an ambiguous law from not properly clarifying poultry ordinances in the 80's.
Several people around town began having chickens and a huge backyard henhouse movement gained momentum, so the city decided it ought to clarify the ordinance quickly. They ruled IN chickens and ducks.
This was April of this year. If you go to my BYC page, I have a link to the ordinance and the letter to the commission recommending the change.
It's very basic, and many cities can simply modify an existing ordinance to include chickens as pets, so that all of the same humane care is required. Most noise ordinances are written so that they would already apply, as well as how clean the property must be kept. Very little needs to be added or defined, as much falls into existing law.
Generally, just the number or birds, whether or not roosters may be kept, and sometimes a specific clearance from others' homes is all that needs definition.
Best of luck!