Post by jonsdigs on Dec 13, 2006 17:07:32 GMT -5
Bats speak up to avoid a jam
00:01 13 December 2006
NewScientist.com news service
Roxanne Khamsi
Brazilian free-tailed bats have to carefully avoid using the same echolocation calls as their neighbours (Image: Erin Gillam)
Bats can locate their prey using echolocation without confusion even when immersed in a thick swarm of many hundreds of other bats, and now researchers have discovered the secret. The winged mammals raise the pitch of their echolocation calls to make them stand out against "jamming signals".
The finding helps explain how hundreds of bats can hunt in the same area without getting confused by others' calls, and could perhaps inform the design of better radar systems for aircraft.
Bats use the echo pattern of their voice to locate insects and other prey – so confusing echoes can cost them dinner. A new study reveals that the flying mammals use a wide range of pitches and simply raise the pitch of their echolocation calls to stand out against other bat calls at the same frequency.
Erin Gillam of the University of Tennessee in Knoxville, US, and colleagues conducted experiments on Brazilian free-tailed bats (Tadarida brasiliensis) in the wild.
The bat cave
The team positioned itself at a site near a bat cave where the animals typically forage one at a time. When a bat came to the site, scientists recorded its sounds while simultaneously playing pre-recorded echolocation calls at various pitches through a portable speaker.
In this soundfile (wav format), listen to the different echolocation noises used by the bats, including the search phase, approach phase and “feeding buzz” made when the animal gets very close to an insect. The sound has been manipulated by a computer into a frequency range audible by humans.
An analysis of the recordings made at the site revealed that bats did not change their calls when these differed in pitch from the pre-recorded ones by at least 3 kilohertz.
But when the difference was less than 3 kHz, the animals raised the pitch of their calls above those from the speakers to achieve this difference in just one-fifth of a second (200 milliseconds). For example, if a foraging bat’s initial calls registered at 26 kHz and it encountered a 24 kHz playback, it would shift its pitch up to 27 kHz. Brazilian free-tailed bats have a frequency range of 20 to 40 kilohertz.
Fighter jets
Surprisingly, even bats that used calls below the playback’s frequency shifted their frequencies upwards. Gillam does not know why the bats would shift their voices up and not down.
But she stresses that the study is an important demonstration of the bats’ ability to avoid potentially interfering noises. "This is the first time that people have tested experimental jamming signals on mammals," she explains.
Gillam says that a better understanding of how bats shift their pitch so swiftly to avoid jamming signals could help engineers design better radar systems for fighter jets. While such jets are highly sophisticated, they lack the capacity to dart amongst 100 other planes that are moving at the same speed in a small airspace.
"Bats can perform such complicated tasks, and seem to move amongst large numbers of bats with relatively few or no collisions," Gillam says. "If developers of radar and sonar can gain any information as to how bats process their echolocation signals and achieve these highly complex manoeuvres, it would be highly beneficial."
Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2006.0047)
Article
See Also Bats use sonar to talk to each other
00:01 13 December 2006
NewScientist.com news service
Roxanne Khamsi
Brazilian free-tailed bats have to carefully avoid using the same echolocation calls as their neighbours (Image: Erin Gillam)
Bats can locate their prey using echolocation without confusion even when immersed in a thick swarm of many hundreds of other bats, and now researchers have discovered the secret. The winged mammals raise the pitch of their echolocation calls to make them stand out against "jamming signals".
The finding helps explain how hundreds of bats can hunt in the same area without getting confused by others' calls, and could perhaps inform the design of better radar systems for aircraft.
Bats use the echo pattern of their voice to locate insects and other prey – so confusing echoes can cost them dinner. A new study reveals that the flying mammals use a wide range of pitches and simply raise the pitch of their echolocation calls to stand out against other bat calls at the same frequency.
Erin Gillam of the University of Tennessee in Knoxville, US, and colleagues conducted experiments on Brazilian free-tailed bats (Tadarida brasiliensis) in the wild.
The bat cave
The team positioned itself at a site near a bat cave where the animals typically forage one at a time. When a bat came to the site, scientists recorded its sounds while simultaneously playing pre-recorded echolocation calls at various pitches through a portable speaker.
In this soundfile (wav format), listen to the different echolocation noises used by the bats, including the search phase, approach phase and “feeding buzz” made when the animal gets very close to an insect. The sound has been manipulated by a computer into a frequency range audible by humans.
An analysis of the recordings made at the site revealed that bats did not change their calls when these differed in pitch from the pre-recorded ones by at least 3 kilohertz.
But when the difference was less than 3 kHz, the animals raised the pitch of their calls above those from the speakers to achieve this difference in just one-fifth of a second (200 milliseconds). For example, if a foraging bat’s initial calls registered at 26 kHz and it encountered a 24 kHz playback, it would shift its pitch up to 27 kHz. Brazilian free-tailed bats have a frequency range of 20 to 40 kilohertz.
Fighter jets
Surprisingly, even bats that used calls below the playback’s frequency shifted their frequencies upwards. Gillam does not know why the bats would shift their voices up and not down.
But she stresses that the study is an important demonstration of the bats’ ability to avoid potentially interfering noises. "This is the first time that people have tested experimental jamming signals on mammals," she explains.
Gillam says that a better understanding of how bats shift their pitch so swiftly to avoid jamming signals could help engineers design better radar systems for fighter jets. While such jets are highly sophisticated, they lack the capacity to dart amongst 100 other planes that are moving at the same speed in a small airspace.
"Bats can perform such complicated tasks, and seem to move amongst large numbers of bats with relatively few or no collisions," Gillam says. "If developers of radar and sonar can gain any information as to how bats process their echolocation signals and achieve these highly complex manoeuvres, it would be highly beneficial."
Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2006.0047)
Article
See Also Bats use sonar to talk to each other