Bat Echolocation Is Intense

If you think rock concerts are loud, you should hear the bats. An
article published in the open-access journal PLoS ONE
finds that bats emit sounds that are above the human threshold
of pain.



Researcher Annemarie Surlykke (Institute of Biology, SDU, Denmark) and
her colleague Elisabeth Kalko (University of Ulm, Germany) investigated
the patterns and behavior of echolocation in 11 species of
insect-eating tropical bats from PanamГЎ. The bats use a sonar system to
capture insect prey at night, and the researchers reconstructed these
flight paths using arrays of microphones and photographic methods.
These models were used to estimate the intensity of sound that was
emitted during the flights.



Surlykke and Kalko found that bats emit a sound that is stronger than
any other animal in air. The exceptionally loud sounds exceed 140
decibels (dB) SPL (Sound Pressure Level measured at 10 cm from the
bat's mouth). This is louder than the 115 - 120 dB that is emitted at a
loud rock concert and the 120 dB human threshold of pain.



Humans, however, cannot hear the echolocation call since the bats emit
sounds at ultrasonic frequencies. They do this in order to find the
location of small insects that would be missed using lower frequencies.
These high frequencies, though, do not travel as far in air as
low frequencies because of air's ability to attenuate the sound. The
researchers used estimates of the detection range for typical insect
prey to conclude that extremely intense, ultrasonic sounds are
necessary in order to counteract this attenuation.



Another interesting finding was that bats that emit the highest
frequencies were also the ones emitting the highest intensities. This
first comparative field study of bat echolocation sounds found a wide
variation of signal intensities and frequencies that converged on
similar detection ranges.



"Overall, our study underlines the importance of intensity
measures in the field as source level plays a crucial and so far
largely underestimated role in bat echolocation. If we want to further
understand which ecological and evolutionary factors shape echolocation
signal design, an even larger variety of call parameters need to be
considered, including sound duration and pulse interval, which may
create call-echo overlap or other masking effects," conclude the
authors.



Echolocating Bats Cry Out Loud to Detect Their Prey

Surlykke A, Kalko EKV

PLoS ONE (2008). 3(4): e2036.

doi:10.1371/journal.pone.0002036

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Written by: Peter M Crosta