How does humming bird hums?

Humming birds are among the smallest birds. 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 activitey.That's why humming bird hums to conserve their energy