I may have missed it on the thread but can anyone advise me on how to acclimate my birds to cold weather? Im about to move at the end of the month from sunny southern California to South Dakota. I'm really worried about the well being of my birds. They are all pretty cold hardy breeds (except for the guineas) but they've never had to deal with weather colder than 40 degrees F. Any advice would be appreciated.
They should be ok and acclimate on their own.
That means that as the air cools down, day after day, their bodies are signaled to grow more feathers, specifically the small, downy ones that are close to their skin. Their bodies will also work harder at pumping blood to extremities to help protect them from frost bite (thus the discussions about the appropriate feed for the winter; they need good fuel to keep that blood pumping and not wear them out).
As long as you don't have a sudden change in temp (where the temp drops 30-40 degrees, and then it stays there or below for the rest of the winter), the birds should make it fine. Most places (where it snows), the fall season is a series of warm and cold days. Some days the weather is nice and almost summery, and other days it is chilly, rainy or frosty and it'll alternate until early to late November where it will settle into a normal daily winter temp.
Animals use those days to gear up or acclimatize for winter. It isn't anything you do except to not interfere with it. You have to let them be chilly. There is nothing else that makes their bodies grow those extra feather except for that they need them. They are just genetically encoded to protect themselves. The cold hardy birds simply respond faster and better, but all birds will do it to some extent.
I don't recall if you mentioned how old your birds are. If they are really young, like before they have feathers, you might have to help them until they get those feathers, but I'll defer to anyone who has acclimatized chicks without mothers. Usually, moms would help in that process by keeping their babies warm as needed, but if you have real young ones without moms, you'd have to provide warm places and bedding where chicks could get out of the elements. Just a spot though, not the entire coop. They still would need to be cold at some time, off and on, to trigger that natural process of growing more feathers, etc.
Hope that helps some.