during winter it really helps to bump up protein and fat, lots of scrambled eggs etc. and make sure they can always fill their crop before they go to sleep, thats what keeps them warm through the night, burning off the food in their crop. I'v had people around me say they've kept them in open aviaries all winter with only a few losses, and they probably did, however in my opinion this is inhumane and shouldn't be done, they need some kind of shelter. In the winter the smaller the better, a largish modified rabbit hutch with solid sides would be great as long as it wasn't too open to the elements and the birds all got locked in at night. Heat lights are not usually necessary, but you may need them, i only use them on the coldest nights of the year (below zero, we usually only have 10 or so of these) in Michigan you may need to use them more, I'd try to keep the temperature at or around 10 at least. In the winter the more birds the better, they can all bunch together and add warmth to the shelter, with 5+ birds in a small enclosure the temperature starts going up. Always use flat perches or else they will lose toes to frost bite. I'd suggest feeding a balanced dove food, like kaytee, or if you can find a cheaper wild bird food mix with the same composition of seeds use that, you can also try adding stuff, i feed my doves and pigeons a 1:1:1 mix of cracked corn, dove seed, and gamebird feed, they all seem to be doing fine. Around fall start giving them lots of fat and protein, hard boiled or scrambled eggs, old bread (crumbs), pretty much anything they'll eat. good luck