While I agree that a bird should be acclimated to cold weather (freezing or below F), but they are built to handle cold temperatures.....our birds have at least four layers, maybe five of insulation.....air space, down feathers, air space, secondary feathers, air space, primary feathers.....the various layers of feathers can be raised and/or lowered to increase heat retention as necessary.....this is where the caution against wind/breeze comes into play as blowing cold air can quickly usurp the built-in heat reserve a bird can generate.....
Our feathered friends have another built-in way of helping keep warm.....since there are very few blood vessels in their legs & toes, the veins/vessels in their legs are located right next to each other, so that fresh blood warms the legs & feet. In cold weather birds are able to constrict the blood vessels in their toes and legs so that they don't loose heat from walking or perching on cold/icy surfaces.....it may be hard to believe, but birds do not feel cold in their feet like we would if we walked around barefoot on icy sidewalks.....then there's the fact that a bird can sit down on its lower legs & feet to provide additional heat.....
Don't get me wrong, I'm not advocating keeping our birds in cold weather, but our feathered friends are really better prepared to handle cold weather than we humans are.....
We humans wear sweaters because we don't have any built-in way to create our own added insulation, but I've often wondered how much warmth bird sweaters/coats actually provide our birds or may have prevented our birds from properly regulating their own warmth, so have never gotten any for any of my birds.....
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