I second everyone else - they need wind protection. If there is no wind, then the feather insulation plus heat lamp should be enough (and other warm bodies). If there is wind - it will cut that heat away from their bodies too quickly and their feathers - though initially and for a short time do the job - will not be enough, and the general stress on them will take its toll. They need wind protection even if it means making their space smaller. I know folks that use hay or straw bales.@bardies, will it be a shock to their system to put them outside in December? I certainly understand letting them get some body fat and more feathers.
@trues - hoping our weatherman is correct on Sunday! Would love to put the little ones outside on still green grass.....