Layman's version:
Up to twenty animals of mixed combination. Chickens must be kept five feet from a neighbor’s fence or property line, and they must be kept 20 ft. from neighboring dwellings.
 The Urban Chicken ordinance on the books:
Link to municipal code online: Title 9: Animal Regulations
Text of municipal code:
As used in this title, unless the context clearly indicates otherwise, the following definitions shall apply.
A. "Animal" means any nonhuman mammal, bird, reptile, amphibian or fish including, but not limited to dog, cat, horse, goat, sheep, and chicken and all animals defined in California Penal Code Section 597.
G. "Domestic birds" means any of a class (ayes) of domestic warm-blooded vertebrates distinguished by having the body more or less completely covered with feathers and the forelimbs modified as wings.
9.08.050 Keeping domestic birds.
It is unlawful for any person to keep on any premises in the city any domestic bird as defined in Section 9.04.020, unless such birds are kept in an enclosure. No part of such enclosure shall be within twenty-five feet of any dwelling houses occupied by human beings other than the person’s own dwelling; provided, however, that a domestic bird may be kept temporarily at a pet shop or other place of business for purposes of sale. (Ord. 2185 NCS §2 (part), 2004.)
9.08.060 Sanitation of bird enclosures.
It is unlawful for any person to keep domestic birds on any premises, unless coops and enclosures in which such birds are kept are maintained in a sanitary manner and are regularly cleaned at least once each week, in order to prevent any accumulation of manure or offal. Violation of this section constitutes a public nuisance. (Ord. 2185 NCS §2 (part), 2004.)
9.08.070 Birds, rabbits, rodents and reptiles — Maximum number permitted.
No person shall keep or have upon any premises owned, occupied or controlled by him/her within the city, domestic birds, rodents or reptiles exceeding at any one time twenty in number. Such number shall be construed to mean twenty in the aggregate or total of number of such animal, regardless of the particular kind or age of the animal. No person shall keep or have upon any premises owned, occupied or controlled by him/her within the city at any one time twelve or more rabbits. (Ord. 2185 NCS §2 (part), 2004.)
9.08.080 Sanitation of dog shelters and other animal enclosures.
It is unlawful for any person to maintain any animal on his premises in a manner so as to cause the accumulation of manure, offal or feces, which cause the attraction of flies or vermin, or create smells which interfere with the use and enjoyment of any neighboring properties. All yards and other enclosures in which dogs or other animals are kept shall be maintained in a sanitary manner and regularly cleaned at least once a week to prevent the accumulation of manure, offal or feces. (Ord. 2185 NCS §2 (part), 2004.)
9.08.090 Location of dog shelters and other animal enclosures.
All dog shelters, domestic fowl enclosures, pens and other animal enclosures shall comply with the location requirements specified in the Petaluma zoning ordinance. (Ord. 2185 NCS §2 (part), 2004.)
9.08.100 Straying of domestic birds or livestock.
It is unlawful for any owner and/or possessor of any domestic bird or livestock to suffer or permit the same to stray from premises and to enter or remain on public property, including any highway or street, or onto private property whose owner or occupant has not provided permission for entrance upon his premises. The owner and/or possessor of such animals shall be liable to the city for the salary, costs and expenses incurred by the city in restraining, capturing or rescuing domestic birds or livestock which have strayed from the premises of the owner/possessor thereof. (Ord. 2185 NCS §2 (part), 2004.)
9.08.110 Entry of dog on premises maintaining livestock or fowl.
No owner and/or possessor of a dog shall suffer or permit the dog to enter upon the premises of another person where livestock of domestic fowl are maintained without the consent of the owner or occupant of the premises. (Ord. 2185 NCS §2 (part), 2004.)