Although the scientists studied only insect-eating bats with comparable feeding habits, they found major differences in the species' voices.
Different species called in different frequencies, and some were much louder than others.
"We found these extreme differences in emitted intensity, up to 140 dB for the loudest down to 120 dB for the most silent of the bats in our study," she said.
A 20 dB difference equals a tenfold increase in sound pressure, according to Surlykke.
Yet louder and quieter bats all seemed to detect their insect prey at about the same distance—typically some seven to ten feet (two to three meters) away.
"That surprised us because the differences in immediate intensities are quite big," Surlykke said.
Results of the study were published this week in the journal PLoS ONE.
Loud, But Not Far
Some bats apparently turn up the volume in order to compensate for their high-frequency calls, which don't carry far and weaken quickly.
"Ultimately there are limits to what the mammalian ear can detect," said Cynthia Moss, principal investigator at the University of Maryland's Auditory Neuroethology Laboratory.
"Bats that produce high-frequency sounds can't push their hearing to detect sounds that are really weak in the environment," said Moss, who was not involved in the new research.
"They push the output of the vocalization to end up hearing echoes at about the same level," she said.
Study co-author Surlykke noted that the ability is likely a critical survival adaptation.
"They may have to adjust the volume to get a reasonable detection distance to operate," she said.
"If the [distance] was too short they wouldn't be able to react if they did detect prey."
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