I don't know about birds during these "dark" times, but todays birds are pretty resilient to wide change in temperature even on a daily basis. They are capable

I don't know about birds during these "dark" times, but todays birds are pretty resilient to wide change in temperature even on a daily basis. They are capable of generating and circulating fair amount of body heat. Their average temperature is typically much higher than mammals. They are also well insulated, more than humans, apes, dogs, cats...