How do bats find food in the dark?

Bats are not blind

You may have heard someone say "blind as a bat". It is not true! Bats can see. But many bats also hunt in the dark, when even good eyes cannot see much. Australia has two very different kinds of bats, and they solve this problem in two different ways.

Bats are the only mammals that can truly fly. Australia has more than 80 kinds, or species. Most of them are microbats, small bats that mostly eat insects. They weigh from about 3 grams up to about 150 grams. The others are fruit and nectar eaters. The biggest of these are the flying-foxes. Some have wings that stretch more than a metre from tip to tip. Their faces look a bit like a fox's, but they are not closely related to foxes at all.

Shout, then listen

A microbat finds its way in the dark using echolocation. That means finding things by listening for echoes. The bat makes a very short, high-pitched call in its voice box. The call comes out of its mouth or its nose. The sound hits something, such as a moth, and bounces back as an echo. The bat's ears catch the echo.

An echo tells the bat a lot. The longer it takes to come back, the further away the object is. The bat can also tell which way the object is, and what kind of thing it is. It is a bit like shouting across a valley and listening for your voice to bounce back. The bat does it again and again, many times every second.

Light is not needed, so a dark night makes no difference. Almost all of these calls are ultrasonic, which means they are too high-pitched for people to hear. Microbats use other sounds when they talk to each other, mostly in their roosts.

The chase

Picture a microbat flying through the bush at night. While it is cruising, it makes about 10 calls every second. Then an echo comes back from a moth. Now the bat speeds up. As it closes in, it makes more than 100 calls every second. This fast burst of calls is called a feeding buzz. Each call gives the bat a fresh check on where the moth is.

Most microbats catch their food while flying. A few hunt on the ground on all fours. Between them they eat moths, beetles, flies, mosquitoes, ants and many other insects. In one night, a microbat can eat at least a third of its own body weight in insects. Many of those insects are pests, so bats help farmers, and they help anyone who does not like mosquito bites.

Each kind of microbat has its own tricks. The golden-tipped bat feeds almost entirely on spiders. The large-footed myotis, also called the fishing bat, has big feet with long, curved claws. It flies low over a stream or lake and rakes the water to catch small fish and water insects. Some long-eared bats are very quiet hunters. They "whisper" their calls, and when they get close to a moth they can switch the calls off and listen for the flutter of its wings instead.

You cannot hear most bat calls, but there is one you can. The white-striped free-tailed bat has the lowest-pitched calls of any Australian bat, and most people can hear them. After dusk, listen for a regular, metallic "ting...ting...ting" in the night sky.

Eyes and noses, as well as ears

Some bats use more than their ears. The ghost bat of northern Australia is the largest microbat, and it is Australia's only meat-eating bat. It eats large insects, frogs, lizards, birds and small mammals, even other bats. A ghost bat uses echolocation, but it also has big eyes and sharp hearing. It swoops on its prey, kills it with a powerful bite, and flies off to a feeding site to eat.

Flying-foxes go one step further. These are the large bats you may see flapping over a city at dusk, and they do not use echolocation at all. They use their eyes and noses. Their big, forward-facing eyes see much better in low light than ours do. They also have an excellent sense of smell, which helps them find ripe fruit and flowering trees.

A flying-fox leaves its daytime roost, called a camp, around sunset. A grey-headed flying-fox can travel up to 50 kilometres to its feeding area. It uses rivers, roads and even streetlights as landmarks, and it remembers places where it has fed before. It eats fruit, especially figs, and it drinks nectar from the flowers of trees such as gums.

While it feeds, pollen sticks to its fur. It also carries seeds away from the tree they grew on. Flying-foxes can spread pollen and seeds over much longer distances than birds or insects can, which helps to keep forests healthy. Sadly, grey-headed flying-fox numbers are falling because so much of their habitat has been cleared.

Keeping bats and people safe

Bats are wild animals, and they are best left alone. In Australia, any bat could carry a virus called Australian bat lyssavirus. It can pass to people through a bite or a scratch. This is very rare, but it is serious. So the rule is simple: never touch a bat, even if it looks sleepy, hurt or dead. Tell a grown-up, who can call a wildlife rescue group.

There are plenty of other ways to help bats. Keep pet cats indoors at night. Leave old trees with hollows standing, because many microbats sleep in them by day. Put up a bat box and turn off extra outdoor lights. In cooler places, microbats hibernate in winter, so never disturb a bat that is tucked away asleep. Waking it uses up the fat it needs to survive until spring.

📚 Words to know

Echolocation

Finding things by sending out sounds and listening for the echoes that bounce back.

Ultrasonic

Too high-pitched for people to hear. Most microbat calls are ultrasonic.

Microbat

A small bat. Most Australian bats are microbats, and most of them eat insects.

Flying-fox

A large bat that eats fruit and nectar. It finds food with its eyes and nose, not with echolocation.

Roost

A place where bats rest or sleep in the daytime, such as a tree hollow, a cave or a flying-fox camp.

🧪 Try this: play bat and moth

1. You need at least three players, a grown-up to watch, and a grassy space with no steps, poles, roads or water nearby. One player is the bat. The others are moths.
2. The bat stands in the middle and closes their eyes (no peeking!). The moths spread out around the bat and stand still, a few big steps away.
3. The bat calls out "Bat!" Every moth must answer "Moth!" The bat listens, then walks slowly towards a moth with their hands out in front. The bat can call again whenever they like. When the bat gently tags a moth, that moth becomes the next bat.
4. Think about how it felt. How did you work out where a moth was, and how far away? Was it easier when the moths answered loudly or softly? Real bats do this in the dark, in a split second, while flying fast.
5. Challenge: find a big, flat wall, such as the side of a school hall, and stand a long way back from it. Clap once, loudly, and listen for the echo. Move closer and clap again. Does the wait for the echo change? Real bats use that wait to judge distance.