Buy an Alfalfa bale and put out a flake...Mine go crazy pecking and kicking it all over...Gives them the feeling of foraging...I hid Raisins and scratch in it...While I'm a "southerner" by comparison to you Wyoming and Canada folks, we do get down to zero and some snow here on the Kansas plains. For mine I think it's less about the temps than it is the lack of appeal for what chickens like to do that keeps them mostly in the coop during cold days. Mine detest snow and almost always stay in the coop on those days. But even on frigid days without snow on the ground, there really isn't as much interest in scratching around - I think they instinctively understand pickings are slim so they just don't make as much of an effort. Of course I supplement their winter of being cooped up with extra scratch and treats.