HOW COME? Bats use their ears, not eyes, to find food

How can bats catch insects in the dark? asks a reader.Bats come out at dusk, swooping across yards and fields like flapping vacuum cleaners. While we can't see what they're doing in the dim light, they are actually snatching up insects as they go.

During the day bats hang around home -- in the rafters of a barn, a hollow tree or a handy cave. A bat's day is spent dozing and grooming itself, mostly while upside down.

Around sunset, bats fly off in search of food. While some bats eat fruit or frogs, and tropical vampire bats feed on the blood of other animals (like cows), most bats eat lots and lots of bugs. In fact, some can swallow 25 percent of their own weight in teeny insects, in just half of a twilight hour.

Like many other animals, such as coyotes, bats prefer to hunt under the cover of darkness. Bats use vision to navigate at dusk. But to locate insects, say, 40 feet away, bats rely on echolocation. Sound sent out and returned can detect the exact location of small insects flying across a background of trees, a feat that would be difficult or impossible using sight alone. And in total darkness a bat relies on its sonar to keep from running into the nearest tree.

Flying bats emit rapid, high-pitched chirps through their mouths or noses, using their big ears to listen for sound reflections. A bat may sweep your yard with sound at 10 or more blips a second, looking for insects. When the sounds echo off a bug, the bat chirps faster, to get a better sense of the insect's size and location. Some bats may catch more than 1,200 insects an hour.

Bats are mammals, animals that make milk to feed their young.

Out of the more than 5,400 mammal species on Earth, more than 1,200 are bats -- the only ones that can fly. Now scientists think that bats may also be the only mammals with "superfast" muscles, which can contract 100 times faster than ordinary muscles.

Researchers knew that superfast muscles power the twitters and trills of songbirds, as well as a rattlesnake's rattle. Now, they've discovered that the muscles also allow bats to take rapid-fire sonar snapshots of their surroundings. As a bat zeros in on a bug, it may chirp 190 times a second; superfast muscles make it possible.

Bats even use sonar to detect ripples in a dark pond at night. The tungara frog of Central America falls silent if it thinks a bat is around. But the ripples created by its half-submerged mating call continue spreading for a few seconds, allowing a bat time to swoop in for the grab.