Budgerigars are from the Australian outback originally, where temps get up to 120F. Most of what you see now are far removed from the wild budgies, but they still require warmth. Unless your winter night time temps stay at or above 60F, your budgies will not be happy. They can not handle cold drafts or extended temps below 58 F to 60F.
http://www.budgie-info.com/bud...
