On these intensely cold days, the birds hit the feeders before sunrise to replenish their energy for the day. I found this cardinal digging around at the base of one of the feeders and realized it must be mostly empty.
Sub-zero temperatures make the suet cakes concrete-hard so that the woodpeckers have to drill them to get a bite.
Animals convert their daily food intake to fat stores, which are then metabolized overnight at a prodigious rate. Black-capped Chickadees, for example, can turn-over 25% of their body weight overnight on a very cold night.
But energy costs (metabolic rate on the Y-axis below) go up as the temperatures go down (on the X-axis below), and the smaller the animal, the higher that rate of fuel consumption and energy burn, as shown in the graph below.
At some point, there is a limit to how much heat a small animal like a Downy Woodpecker can produce in order to stay warm, and still make it through the night revving its furnace to that high level. A friend of mine found that 80% of the Downy Woodpeckers they tested in the winter in South Dakota became hypothermic (3-5 degrees below normal) after 30 min exposure to 5F, which leads me to wonder how these birds are faring at our current below 0F temperatures.