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To conserve energy, a hummingbird can go into a sleep-like state known as "torpor." During torpor, the tiny bird's body temperature can drop by 50 degrees, the heart rate can slow from 500 beats per minute to fewer than 50, and breathing may even stop for a period of time. A hummingbird uses as much as 50 times for energy when awake than when torpid, but a torpid hummer can't respond to emergencies.
They will often do this when it's cold outside at night.
