Acoustic warfare: bats jam each other's sonar while bug hunting

Reuters News
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Posted: Nov 07, 2014 5:07 PM

By Will Dunham

WASHINGTON (Reuters) - All's fair in love and war - and also in mid-air bug hunting, if you're a bat.

Scientists studying a common species of these flying mammals found that the bats, while competing for the juicy insects they call dinner, make noises that "jam" other bats that are using their sonar-like echolocation abilities to zero in on prey.

Echolocation - bouncing sound waves off objects - is how bats navigate in the dark while hunting, enabling them to find and catch elusive insects zipping through the nighttime air.

Sophisticated video and audio recordings made during experiments in Arizona and New Mexico involving Mexican free-tailed bats revealed how they thwarted each other's meal plans.

Just as one bat was within a split second of snatching a moth or other insect in mid-air, another bat that was also out foraging used its vocal chords to emit a specialized jamming call to prevent the first one from making the catch.

"The bats jam competitors to prevent them from capturing insects so that the jamming bat has an opportunity to catch the prey," biologist Aaron Corcoran of Wake Forest University in North Carolina, who led the study published in the journal Science, said on Friday.

"The hunting bat is 86 percent less likely to capture the prey when it is getting jammed," Corcoran added.

The researchers said this is the first bat species known to use jamming but it is possible other bats do it as well.

The jamming call has a pitch that rapidly moves up and down, covering the frequencies used by bats to locate and capture insects, Corcoran said. The hunting bat simultaneously hears the jamming call and the echoes from its own echolocation, preventing it from being able to calculate the bug's position, he added.

"This is nature's version of acoustic warfare," Corcoran said.

The jamming is akin to techniques used in modern aviation warfare. "I liken it to a pilot jamming the radar of an incoming missile," said Wake Forest biologist Bill Conner, another of the researchers.

Battling for bugs is particularly challenging for these bats considering that they often live in colonies of millions of individuals all wanting the same kind of meal.

"The jamming call is an oscillation in frequency like the vibrato of an opera singer. We, of course, cannot normally hear it because it is too high in frequency. When you lower the frequency into our range, it sounds somewhat like bird song," Conner said.

The Mexican free-tailed bats, scientific name Tadarida brasiliensis, are medium-sized bats with brown fur, large ears and a wingspan of about 11 inches (28 cm) found in the western United States, Mexico, Central America and northern South America.

This study showed that bat sounds have at least three functions: echolocation, intraspecies communication and acoustic interference. The bats are known to make at least 15 different communication calls for purposes including attracting mates, young bats calling for their mothers and males fending off other males.

(Reporting by Will Dunham; Editing by Sandra Maler)