p2pnet - rss feed: Tuning in to squirrels
p2pnet.net OT News:- Here’s another in our occasional ‘it doesn’t have a lot to do with p2p, but it’s interesting anyhow’ series, and it poses the question, What do squirrels, dolphins and bats have in common?
Easy: they’re all mammals.
Nope.
They all fly (like, bats fly, there are ‘flying’ squirrels, dolphins ‘fly’ under water)?
That’s really stretching it and it’s wrong anyhow.
They all ’squeak’ to communicate?
Yep. But there’s more to it.
Under discussion is Richardson’s ground squirrel, found in North America. They don’t just make noises; they’re ultra-sonic, and it’s the first time an animal has been found to use high-frequency sound this way, say University of Manitoba researchers David R. Wilson and James F. Hare in their Animal communication: Ground squirrel uses ultrasonic alarms.
“[…] a purely ultrasonic signal is produced in the wild by a rodent of the Sciuridae family, Richardson’s ground squirrel, and show that its function is to warn conspecifics of impending danger,” says a report on their work in Nature here. “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.”
“In 1993, Hare was studying a group of Richardson ground squirrels when he noticed their mouths were opening as if to make a sound - but only quiet breaths of air were coming out,” says a story in the Winnipeg Sun here, going on:
“He wondered whether the squirrels were actually communicating with sounds that were too high-pitched for the hearing range of humans and many other mammals. Hare borrowed a bat detector from a friend and found out the inaudible calls were in the ultrasound range.”
He was right. The ‘quiet breaths’ were in fact ultra-sonic calls in the 50kHz range, “placing them way beyond the hearing of humans and of predators as well,” says South Africa’s Independent Online here, adding:
“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.”
July 30th, 2004 at 3:16 am
I would probably disagree with the significance of the concept of “ultrasonic” as it relates to animals. Each species has its own individual range of hearing - an audible frequency range that often may be outside of the human range of hearing. The terms “ultrasonic” and “subsonic” apply to the range of human hearing only, so these terms might not be appropriate when referring to other species’ interactions.
From tiny insects to great whales, many animals communicate using ultrasonic frequencies. Elephants use subsonic frequencies for the purpose of locating each other that can be audible (to them) for miles. Maybe if the range of human hearing was not so genetically limited, we would not be using the label “ultrasonic” nearly as much.
The ground squirrels mentioned converse at 50 khz, which is only just barely outside the measured audible range of domestic dogs, for instance - so perhaps some predators in the wild can actually hear the squirrrels, as evolutionary natural selection would probably favor this ability.
Audible range for various animals in hertz:
Humans 20- 20,000
Cats 100- 32,000
Dogs 40- 46,000
Horses 31- 40,000
Elephants 16- 12,000
Cattle 16- 40,000
Bats 1,000- 150,000
Grasshoppers and locusts 100- 50,000
Rodents 1,000- 100,000
Whales and dolphins 70- 150,000
Seals and sea lions 200- 55,000
September 4th, 2004 at 5:00 pm
In fact ultrasonic frequencies are present in human screams. we are unaware of that energy because we are more sensitive to lower frequencies. Human can indeed hear ultrasound, but generally only by bone or fluid conduction to the ear (lenhardt et al, 1991 Science)