Alice Waterman, age 11, of Oriy Falls, for her question;

How does a hummingbird hum?

His tiny wings beat too fast for star eyes to see. when we watch him fly, zooming like an arrow this way and that, we see only a hazy blur of those fast beating wings. But we can hear them. They beat through the air so fast that they create a whirring hum. This is the soft purring hum we hear when we get close to a busy hummingbird.

The hummer's tiny wings beat about 55 times a second .  which is 3,000 or 4,000 times a minute. He can make his wings move in circles like the blades of a heliocopter. This is why he can hover in the air and even fly backwards.