Hi WyoDreamer,
We have had chickens here for about 4 years now. We haven't had any issues with weather and we are at around 5000 ft. The biggest concern for poultry when dealing with the cold, is staying out of the wind, blowing snow, etc... If they have a shelter, they can handle the actual cold pretty well. Bigger birds do better as a rule and are more apt to continue laying (some) throughout the winter. But we have had some smaller birds also that we haven't had a problem with. We have a (yes, one (~: ) duck this year for his first winter, so we'll see how he does with not getting body heat from the other birds. We have made him an area with extra hay & protection in the barn that he can get to. As far as other problems unique to WY, I haven't ran across any. Hope this helps and enjoy you're brown eggs when you get them.
cowgirl