Paris - A species of squirrel uses ultrasonic frequencies to provide a warning to fellow members of its group, the first time an animal has been found to use high-frequency sound this way, a study published in the weekly journal Nature says on Thursday.
The unusual rodent is a Richardson's ground squirrel (Spermophilus richardsonii), which makes its home in the prairies of North America.
Canadian zoologists noted that in addition to making audible vocalisations in the eight kilohertz range to other members of their community, the squirrels also made "whisper" calls to each other, which produced only faint sounds of rushing air.
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Analysed closely, these calls turned out to be ultrasonic, in the 50kHz range, placing them way beyond the hearing of humans and of predators as well.
But the signal was strong, averaging 66,8 decibels, which is the equivalent of a loud conversation among humans.
The squirrels would emit these calls if they spotted a low-grade threat. If the threat was urgent, they would make audible calls.
The finding is of interest because ultrasonic frequencies are known to be used by some animals, such as the bat and the dolphin, to pursue prey or locate obstacles, but not for communication.
"To our knowledge, ultrasonic alarm calls have not previously been detected in any animal group, despite their twin advantages of being highly directional and inaudible to key predators," say the authors, David Wilson and James Hare of the University of Manitoba.
The limit of human hearing is about 20kHz. - Sapa-AFP
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