How Bats Find Food
Posted April, 1998
What would you experience if you entered a cave inhabited by a colony of bats? If you had a headlamp or a flashlight, you might be able to watch as the bats soared
through the murky darkness, missing walls, stalactites, and you by mere inches. You might hear some of the bats chattering as they communicated with one another, but you would be clueless
about most of the other sounds bats make, because these sounds are outside your range of hearing. Some of these sounds are made by the bats to communicate with one another, some help
them avoid objects such as intruding humans, and still others help bats find their next meal.
How do bats avoid obstacles and find food as they fly past you in the dark? Most bat species use a sense called echolocation that they share with mammals such as
dolphins and whales. Echolocation is a process similar to radar. Bats send out sound waves with very high frequencies toward objects in their path. When the sound waves hit the object,
they bounce off and are reflected back to the receiver (the animal's ear). The bats interpret these sound waves to determine the location and size of the object.
Some insectivorous bats of Europe and North America obtain most of their food using echolocation. It has been discovered recently that the insects most sought by
bats - moths, lacewings, and mantises - all have evolved mechanisms that allow them to hear the soundwaves produced by the bats. These insects have evolved ears that are tuned to the
frequencies usually emitted by their bat predators. When moths or lacewings hear these frequencies, they take action. Some moths change their flight pattern and exhibit erratic flight,
whereas some change course and fly closer to the ground, both behaviors that help moths evade the bats. Some bat species have responded to this behavior by changing the frequencies they
use for echolocation, but some have gone silent and find their insect prey by passive listening or by visual sighting alone.
What would you predict to be the next strategy to evolve in bats' insect prey? Recent observations suggest that a few insect species have evolved the ability to emit
ultrasonic clicks in response to bat echolocation calls. Scientists hypothesize that such clicks may "jam" the bats' echolocation frequencies, preventing them from using echolocation
to find their insect prey. If this is true, then bats and insects have co-evolved to maintain a balance between predator and prey. Research into this possibility is being conducted in
Canada and Europe.
References
Rydell, Jens, Gareth Jones, and Dean Waters. "Echolocating bats and hearing moths: who are the winners?" Oikos, 73:3, 1995, pp. 419-424.
McCracken, Gary F. "Bats Aloft: A Study of High-Altitude Feeding," Bats Magazine, 14:3, Fall 1996, pp. 7-10.
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