When I woke up this morning, I was worried for the hummingbirds. They are definitely here, zooming in and out of branches on the western edge of Colorado Springs. But they don't deal with cold very well. In fact, when conditions get too harsh, they enter a hibernation-like state called torpor. They drop their body temperature to conserve energy.
In 1832, Alexander Wilson first described hummingbird torpor in his book, American Ornithology. He said, "No motion of the lungs could be perceived ... the eyes were shut, and, when touched by the finger, [the bird] gave no signs of life or motion."
Awakening from torpor takes 20 minutes or more. During arousal, the hummingbird's body can warm up by several degrees each minute and the bird awakens with enough energy reserves to see him through to his next feeding bout.
But if cold weather lasts too long, the birds can essentially starve in their sleep, and never wake up. Let's hope its warmer tomorrow.