To keep chickens from freezing to death:
(1) Make a coop for them in which they are protected from strong winds and wet weather; anything that keeps them dry and sheltered from the wind will work. Many long-time chicken keepers from New England, Canada, and etc. will tell you that you do NOT need to worry about insulation or artificial heat. Just do a quick search here, you'll see what I mean!
(a) Make their roost from a 2x4 with the 4" side facing up, so that when the birds roost, their feet are totally covered by their feathery bellies.
(b) If you are keeping the chickens you have now, lock them up in their coop at night, at least until they are used to roosting indoors instead of out. Generally, they are smart enough to choose a warm house over a cold tree if the night is cold enough, but I can't vouch for California chickens.
You may want to lock them in on any really cold night, just for your own peace of mind, until you know for sure that they are going in there on their own.
(c) It is hard to have too much ventilation in your coop, winter OR summer. In winter, there is a greater danger from the moisture that chickens produce and the ammonia of their droppings than there is from cold or drafts.
https://www.backyardchickens.com/a/...-go-out-there-and-cut-more-holes-in-your-coop
(2) I couldn't tell if you are transporting the 7 chickens you have now or are going to start a new flock. If you are starting over, get breeds that are reputed to do well in cold weather: generally these will be the larger, feathery-er birds with small combs. If you aren't, don't worry about it, they still won't freeze. There are things you can do for chickens with large, single combs to prevent frostbite on the comb, I think some people put a little vaseline on the comb.
(3) Let them outside as much as possible! This keeps the chickens acclimated to the weather, so that they're used to it; the only way I can picture a healthy chicken actually dying from cold would be if it was totally unused to being outdoors (i.e., a house-chicken or something) suddenly being put out. Chickens, like any animal (including us humans!), do best with a lot of outdoor time. Your current setup sounds ideal, if you could duplicate that somehow!
(4) If you get a lot of snow, create a sheltered place where they can be outside without being in the snow itself; a covered run is good, or even just keeping the area closest to their coop shoveled. That way they won't have to choose between running around in the snow, which most chickens don't care for, and being inside their coop.
(5) Some people use heated waterers, there are many threads about them in the "feeding and watering your flock" area. Some just have several waterers and bring a fresh one out every morning, retrieving the frozen-solid one. As long as the chickens have access to water, *how* you manage it doesn't really matter; do what works best for you.
Remember that most chickens do better in cold conditions than hot, and as my husband is always pointing out, they are wearing a down jacket under all those feathers.
For hot conditions, a lot of the advice is the same!
(1) They need access to water at all times. This is the most important thing ever.
(2) Shade, shade, shade! Do not consider the inside of their coop as "shade"; coop interiors are usually even hotter than outside and the birds will not want to hang out there. A covered run, or better yet, access to a yard with trees and bushes-- that will keep your chickens as cool as possible.
(3) Ventilation in the coop, and lots of it.
(4) Just as in winter, the more time the chickens can get outside of their coop, the better.
Hope that helps!
