The key as to weather 2A applies is.
Are chickens household pets?
My answer is no, chickens are not household pets.
The city of Seattle considers chickens and animals kept outside as accessory use animals. The count starts at a 3 + 1 for every 1000 square feet of land beyond the minimum lot size for the residential zone the house is in. The minimum lot size is sometimes 5,000 square feet which for a 20,000 square foot lot in that zone would allow 3 + 15 or 18 chickens.
At the same time this must not be in conflict with the county law or the state law. The upper levels codify the powers that get delegated to the lower levels.
For example if the state says that the local jurisdiction is the only power that can set zoning law, then any attempt by a county if you are in a city to set the rules is moot, likewise any covenant or restriction recorded in the registry that restricts what you can do with your property that is at odds with local zoning is also moot, if the covenants and restrictions do not have a sever-ability clause in them and any clause is mooted by law then the entire covenants and restrictions may be moot.
While some domestic fowl are kept by some people as pets in their homes they are not always considered as household pets by the law.
Seattle Municipal Code for Keeping Chickens
Read the city code about keeping chickens.
Title 23 - Land Use Code
Subtitle IV - Land Use Regulations
Division 2 - Authorized Uses and Development Standards
Chapter 23.44 - Residential, Single-Family
