arf@ddsw1.MCS.COM (Jack Schmidling) (05/17/91)
Article 4431 (22 more) in sci.bio:
From: mll@hpfcso.FC.HP.COM (Mark Luce)
Subject: Sonar: Bats vs. Dolphins vs. Humans
> I am interested in any comparisons of the sonar capabilities of bats,
dolphins, and humans (human technology, of course!). In particular, I have
heard the claim that bats and/or dolphins have certain sonar capabilities
which we have not as yet been able to duplicate technologically. Is there
any truth to this, or is this just another modern folk myth?
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ARF says:
Bats win by a wide margin. In gross terms, electronic sonar can barely
detect a foot long fish. A dolphin can find a golf ball with difficulty
after much forced training. Bats, on the other hand, would starve to death
if they could not pursue and capture thousands of mosquito sized insects, on
the wing, every night.
What gives bats the edge over dolphins is a much higher frequency.
Bats operate from audio to about 100 khz. They alter not only the frequency
but the rep rate as they close on the target to maximize resolution.
Dolphins operate in the human audio range so the amount of data (resolution)
is much less but their normal food is much larger than insects. High
frequency would also be absorbed much faster in water so the range would be
more limited.
The above of course, only applies to insectivorous bats. Many fruit eating
bats have no echo-location capabilities at all.
arf
dean2@garnet.berkeley.edu (Dean Pentcheff) (05/18/91)
In article <1991May17.044756.26698@ddsw1.MCS.COM> arf@ddsw1.MCS.COM (Jack Schmidling) writes: > Subject: Sonar: Bats vs. Dolphins vs. Humans > Bats win by a wide margin.... > What gives bats the edge over dolphins is a much higher frequency.... Wouldn't the speed of sound in the medium have some effect? Sound is _much_ faster in water than in air. Wouldn't that make it much more difficult to measure distances by timing sound echos? -Dean -- Dean Pentcheff (dean2@garnet.berkeley.edu) Department of Integrative Biology, University of California, Berkeley CA 94720
davidh@uhunix1.uhcc.Hawaii.Edu (David A. Helweg) (05/18/91)
In article <1991May17.044756.26698@ddsw1.MCS.COM> arf@ddsw1.MCS.COM (Jack Schmidling) writes: > ARF says: > > Bats win by a wide margin. In gross terms, electronic sonar can barely > detect a foot long fish. A dolphin can find a golf ball with difficulty > after much forced training. Bats, on the other hand, would starve to death have at look at P.E. Nachtigall's chapter "Odontocete echolocation performance on object size, shape and material." in Busnel & Fish _Animal Sonar Systems_ Bottlenosed dolphins can detect wires down to a minimum diameter of .035 cm, and discriminate among targets that vary in thickness by 0.1 cm. > What gives bats the edge over dolphins is a much higher frequency. > Bats operate from audio to about 100 khz. They alter not only the frequency > but the rep rate as they close on the target to maximize resolution. > Dolphins operate in the human audio range so the amount of data (resolution) where did you get this information? Dolphin *whistles* are audible to humans, as is the envelope of both bat and dolphin click trains. Dolphins show adaptive control over click parameters such as peak frequency. In noisy waters (like Hawaii) they tend to shift the peak upward from about 60 to 120 kHz. Bats and Odontocetes have very different echolocation "styles." Bats tend to emit narrow-bandwidth, long-duration FM signals. They probably localize and capture prey using Doppler. Their pulses are not as well-suited for ranging targets as they are for determining velocity. In contrast, dolphins emit broadband, extremely short duration clicks. Their clicks are extremely well- suited for determining target range (by click-echo timing) but aren't really hot for doing velocity. You are right in one (important!) regard -- some prey species of bats have evolved fairly sophisticated "anti-bat" behaviors, such as asynchronous wing beats, diving flights, and even "radar jamming" sound emitted by the moths. No one is sure whether dolphins and their prey species have coevolved to this degree. But the reflective surfaces within fish (eg, swim bladders) are small relative to the size of the fish, so dolphins are doing some pretty decent detection themselves. can you tell I'm a dolphin afficianado? ;-) dah
pamela@bu-bio.bu.edu (Pamela Hall) (05/21/91)
In article <1991May17.044756.26698@ddsw1.MCS.COM> arf@ddsw1.MCS.COM (Jack Schmidling) writes: > > The above of course, only applies to insectivorous bats. Many fruit eating > bats have no echo-location capabilities at all. > > arf > > Just thought you might like to know that most species of bats are not insectivorous, most are fruit, flower and/or nectar eaters. Temperate bat species are almost all (I not sure if it is truly all species) are insectivorous while many more tropical species are non-insectivorous and as most species of bat are tropical, I think this puts insectivorous bats as a minority. Also vision is well developed in old world fruit bats (members of the Megachiroptera?), but the other order (Microchiroptera) are largely, though not exclusively, echolocating species. I also believe that this order has many more species than the Megachiroptera. In the neotropics, Microchiroptera dominate, (maybe even being the only order of bats in the neotropics?), while in the old world tropics both Microchiroptera and Megachiroptera exist. At some point in the not too distant past (maybe 2-3 years ago, in Science) researchers concluded that the Megachiroptera species were actually more closely related to Primates than to Microchiropteran bats! How about that, true flying primates!!! I hope I haven't just told you something you are much better informed about than I! Pamela Hall
deichman@cod.NOSC.MIL (Shane D. Deichman) (05/21/91)
>Wouldn't the speed of sound in the medium have some effect? Sound is >_much_ faster in water than in air. Wouldn't that make it much more >difficult to measure distances by timing sound echos? Not if you were raised on just the one velocity, and had adapted to it. While the reduced time lag may make resolution at short distances difficult, the creatures in question apparently have the ability to discern their target's position well enough that this doesn't make a whole lot of difference. On the other hand, sound velocity is affected by temperature, and water is much more prone to thermal stratiation than air. This would present a bigger resolution problem, calling for multiple repititions to gain a "solution" to intercepting the target.... -shane Go Bears! -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | Shane D. Deichman deichman@cod.nosc.mil | | "There's no heavier burden than a | | <affix favorite disclaimer here> great potential!" -Linus Van Pelt |
davidh@uhunix1.uhcc.Hawaii.Edu (David A. Helweg) (05/21/91)
>tropics both Microchiroptera and Megachiroptera exist. At some point in >the not too distant past (maybe 2-3 years ago, in Science) researchers >concluded that the Megachiroptera species were actually more closely >related to Primates than to Microchiropteran bats! How about that, true >flying primates!!! Eisenberg (_Mammalian Radiations_) classes bats with primates, as he felt that flying lemurs seemed a likely bridge between bats and prosimians. What I find interesting is that Microchiroptera (insect eating echolocating bats) have smaller EQ than Megachiroptera (frugivorous nonecholocating bats). I'd guess that if I had to make up an adaptationist tale, then I would guess that the cognitive demands of remembering food locations for frugivores exceed that of echolocation performance. dah
sarima@tdatirv.UUCP (Stanley Friesen) (05/24/91)
In article <82025@bu.edu> pamela@bu-bio.UUCP (Pamela Hall) writes:
< At some point in
<the not too distant past (maybe 2-3 years ago, in Science) researchers
<concluded that the Megachiroptera species were actually more closely
<related to Primates than to Microchiropteran bats! How about that, true
<flying primates!!!
I too have heard this hypothesis. My impression is that it is still quite
controversial, and is far from universally accepted.
Given the anatomical *similarities* between the two groups of bats,
this concept will require a great deal of evidence to become established.
--
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uunet!tdatirv!sarima (Stanley Friesen)dean2@garnet.berkeley.edu (Dean Pentcheff) (05/26/91)
>Dean Pentcheff writes: >>Wouldn't the speed of sound in the medium have some effect? Sound is >>_much_ faster in water than in air. Wouldn't that make it much more >>difficult to measure distances by timing sound echos? > In article <3075@cod.NOSC.MIL> deichman@cod.NOSC.MIL (Shane D. Deichman) writes: >Not if you were raised on just the one velocity, and had adapted to it.... This reflects a rather old fashioned view of evolutionary biology. The idea that organisms are optimally adapted systems for their environment was discarded some time ago. There are several reasons, some of which have to do with the genetic variation available for selection to act upon. More obviously, organisms are constrained by the physical nature of themselves and their environment. Sensory systems are bound to operate within physical limits. If sound is over four times faster in water than in air (which it is), then the processing system has to be four times more precise to achieve the same result. Eventually, you reach the limits of what neuronal systems can do. One of the interesting differences I ran across is that sound in water is "reciprocal," but not in air. In the water, if a listener at point A can hear sound from point B, a listener at B can hear sound from A equally well. This is not true in air. Wind speeds are suffiently high (relative to the speed of sound in air) that wind shear can refract sound in a non-reciprocal way. Water currents are much slower, so the phenomenon is insignificant there. Evolutionary adaptation cannot sidestep this (or any other) physical phenomenon. -- Dean Pentcheff (dean2@garnet.berkeley.edu) Department of Integrative Biology, University of California, Berkeley CA 94720