Hummingbirds are
among the smallest of birds, most species measuring in the 3–5 in. range. They
hover in mid-air by rapidly flapping their wings 12–80 times per second (depending on
the species). They are known as hummingbirds because of the humming sound
created by their beating wings, which sometimes sounds like bees or other
insects. To conserve energy while they sleep or when food is scarce, they have
the ability to go into a hibernation-like state (torpor) where their metabolic
rate is slowed to 1/15th of its normal rate. When
the nights get colder, their body temperature can drop significantly and thus
slow down their heart and breathing rate, thus burning much less energy
overnight. As the day heats back up, the hummingbird's body temperature will
come back up and they resume their normal activity. They can fly
at speeds exceeding 15 m/s (34 mph); they are also the only group of birds with the ability
to fly backwards. Individuals
from some species of hummingbirds weigh less than a penny.
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