Bats on Tracks

One of the joys of wild nature in Australia is experiencing the peace and quiet at night, broken only by the occasional shriek of a night animal. Thanks heavens I don’t have ears like a bat, I think to myself. When I reach down and turn on my bat detector, the silence is suddenly filled with a cacophony of sound.

The bat detector has converted the ultrasonic (high-frequency) calls of bats into a frequency that humans can hear; thatis, below about 20 kilohertz. Although normally inaudible to us, bat calls are very loud with intensities over 100 decibels (the equivalent of a jet flying over at 300 metres).

Small insect –eating bats, while not blind, usually have tiny eyes and so don’t see fine detail. Instead, they perceive the world in sound. Ultrasonic calls are mostly made in flight, with some bats emitting sound through their nose and others through their mouth. Returning echoes of this sound are received by sensitive ears used to form an image of the bat’s surroundings.

But bats do more than just perceive their surroundings with sound. They are sensitive enough to track the movements of tiny insects even in areas tangled with vegetation. Bat biologists use term clutter to describe vegetation or other obstacles producing unwanted echoes and interfering with a bat’s ability to hunt. The level of sensitivity required to detect the movement of small insects from the clutter is amazing.

The individual pulses of ultrasound produced by most insect-eating bats are not of constant frequency but sweep from high to low. These bats are often referred to as “frequency-modulated” (FM) bats. They use the time delay between the emitted signal and returning echo to estimate the speed and direction of their prey.
We can learn much about the ecology of bats by Studying the frequency of the sounds they emit.


1. The text’s author
A. wishes he had the hearing capacity of a bat.
B. is happy he doesn’t have the hearing capacity of a bat.
C. despises bats on account of their hearing capacity
D. all of the above.

2. Small insect-eating bats
A. mostly perceive the world through sounds.
B. can see minute details that humans are unable to detect.
C. hardly ever hear anything
D. are completely blind.

3. The term clutter denotes
A. noise produced by bats
B. loud sounds emitted by small insects
C. factors that help bats hunt.
D. none of the above.

4. The text claims that we can understand the ecology of bats by
A. destroying the insects they feed on.
B. preventing them from emitting signals.
C. encouraging them to emit signals.
D. studying the periodicity of the sounds they produce.

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