Q: What's the "Acoustic Arms Race" going on in your
backyard this summer?
A: It's the "bats and moths in sonar combat," says
biologist William E. Conner in "American Scientist"
magazine. Animals can hunt either passively by listening
for noises made by their prey, or actively (as most bats and
some whales do) by projecting sounds and then listening for
telltale echoes, called "echolocation." In essence, they
"see" using sound.
Radar ("radio detection and ranging") uses pulses of
radio waves for the "send" signal; sound waves project
better underwater, hence the development of sonar ("sound
navigation and ranging"). "Other than the difference in
signal used, it operates on similar principles to radar."
Functional radar systems were driven by the approach of
World War II. Human-designed sonar predates radar by some
30 years, spurred on by World War I submarines and by the
sinking of the "Titanic," since sonar could be used to
detect icebergs in darkness and fog.
Biological echolocation evolved more than 65 million
years ago in bats, making them masterful hunters that use
short-wave sonar to detect prey as tiny as mosquitoes,
beetles and moths. But the moths have learned to produce
their own sounds to confound the bats' signals. "The ploy
and counterploy of bats and moths comprise a diffuse arms
race... we are just beginning to understand," adds Conner.
Some jamming moths produce their signal only when the bat
has "locked on" to them and the danger is great.
A myriad number of insects ply the nighttime skies,
including 11,000 species of tiger moths and an estimated
200,000 other kinds of moths, not to mention beetles,
katydids, crickets, flies and much more. "Any insect that
flies after dark must have a strategy for dealing with
nature's ultimate nocturnal predators--echolocating bats.
The race is on."
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