How Do They Do It?

How do these little creatures stay alive in cold weather? In the last 24 hours the temperature has plummeted into the 20s, with a wind chill that takes it below zero, and still these little guys flit around without a care in the world. Yesterday I had a hummingbird, actually a couple of them in a territorial battle at the feeder, and today the feeder was solid ice. I noticed that this little fellow was kind of fluffed up and maybe that helps him keep warm, but it still seems impossible in these temperatures. I made sure I threw out several handfuls of food and suet for them. Wherever our renegade pigeons are, they weren't here today so I could sneak-feed the little birds. There were peanuts for the squirrels too, but there weren't many of them out and about.