Another day of extreme cold

Cold records warnings have already been broken in southern Ontario, as yet another day of extremely frigid temperatures looms: -21°C with a winds chill of -30°C to -35°C.
I have wondered how birds survive such brutally cold temperatures. I spent much of the winter sitting in  myhouse, furnace on, wrapped in warm fleece, with a cup of tea. Meanwhile these tiny juncos are regular winter visitors in my backyard.