lip@amid..ARPA (Loren I. Petrich) (09/29/88)
Some questions for anyone knowledgeable: I have sometimes seen (back East, in Ithaca) pairs of squirrels, one chasing the other around. I wonder what this activity is. Is it one squirrel chasing another one off its territory? I doubt that, since I have never seen two squirrels confronting each other (do they actually do that?). Or is it some sort of mating dance? Could it be that the female squirrel gets into heat, and the male squirrel smells her pheromones and starts pursuing her, with the two mating when they finish their peculiar "courtship ritual"? I once saw a squirrel jump with a drop of over six feet (onto a carpeted floor, I might add), and run off as if nothing had happened. Is such durability typical of small animals? If so, then it would be an outcome of the square-cube law, in which smaller animals have a larger drag force (~area~length^2) per unit mass (~volume~length^3). ------------- Loren Petrich lip@and.s1.gov
ray@polya.Stanford.EDU (Ray Baxter) (09/29/88)
In article <22811@mordor.s1.gov> lip@s1-amid.UUCP (Loren Petrich) writes: > I once saw a squirrel jump with a drop of over six feet (onto >a carpeted floor, I might add), and run off as if nothing had >happened. Is such durability typical of small animals? If so, then it >would be an outcome of the square-cube law, in which smaller animals >have a larger drag force (~area~length^2) per unit mass >(~volume~length^3). Six feet is not all that far; humans, chimps and large cats can all handle it. But I take your point, smaller animals, squirrels especially seem especially graceful about it. It think that adaptation is more likely to be the cause of this grace than the proportion of drag to mass. Consider the flights of a rat and a mountain lion. I would be willing to bet that the mountain lion would appear considerably more graceful, in spite being more than 10 times longer. By the way, if the square cube law were to be involved, it would more probably be the cross-sectional area of the animals bones, and not the drag, which was the relevant measure in a fall of six feet.
dean@violet.berkeley.edu (Dean Pentcheff) (09/29/88)
In article <22811@mordor.s1.gov> lip@s1-amid.UUCP () writes: > I once saw a squirrel jump with a drop of over six feet (onto >a carpeted floor, I might add), and run off as if nothing had >happened. Is such durability typical of small animals? If so, then it >would be an outcome of the square-cube law, in which smaller animals >have a larger drag force (~area~length^2) per unit mass >(~volume~length^3). Well, no, not quite. It turns out that (at the sort of sizes and speeds that concern a falling squirrel) drag is proportional to the cross sectional area perpendicular to the fall direction and the velocity squared. To be pedantic: 2 drag = 0.5 * C * rho * S * U D where C-sub-D is the "drag coefficient" and is a fudge factor that accounts (more or less) for shape differences, rho is the density of air, S is the cross sectional area, and U-squared is the velocity squared. The mass falling in gravity results in a force, countered by the drag force (which increases as the _square_ of velocity). Note that for the small mass of a squirrel, the drag force quickly becomes very high, slowing the animal. The animal quickly reaches "terminal velocity", where the force from gravity = the force from drag and the animal stops accelerating. It turns out (and, yes, the experiment was done) that you can drop a mouse from a five-story building with no harm to the mouse - it probably reached terminal velocity around the second story. The situation should be similar for squirrels, particularly given their fuzziness (which should yield a high drag for their mass). If you're interested in a readable account of the relevant biology and physics, see Vogel, S. (1981) Life in moving fluids. Willard Grant. -Dean Dean Pentcheff dean@violet.berkeley.edu To acquire imunity to eloquence is of the utmost importance to the citizens of a democracy. Bertrand Russell
wrp@biochsn.acc.virginia.edu (William R. Pearson) (09/29/88)
In article <4150@polya.Stanford.EDU> ray@polya.Stanford.EDU (Ray Baxter) writes: ]In article <22811@mordor.s1.gov> lip@s1-amid.UUCP (Loren Petrich) writes: ]> I once saw a squirrel jump with a drop of over six feet (onto ]>a carpeted floor, I might add), and run off as if nothing had ]>happened. Is such durability typical of small animals? If so, then it ]>would be an outcome of the square-cube law, in which smaller animals ]>have a larger drag force (~area~length^2) per unit mass ]>(~volume~length^3). ] ] Six feet is not all that far; humans, chimps and large cats can all ]handle it. But I take your point, smaller animals, squirrels especially ]seem especially graceful about it. It think that adaptation is more ]likely to be the cause of this grace than the proportion of drag to mass. ]Consider the flights of a rat and a mountain lion. I would be willing to ]bet that the mountain lion would appear considerably more graceful, in ]spite being more than 10 times longer. ] ] By the way, if the square cube law were to be involved, it would ]more probably be the cross-sectional area of the animals bones, and ]not the drag, which was the relevant measure in a fall of six feet. All of the readers of sci.bio should take a look at the essay: "On being the right size." by J. B. S. Haldane. I will quote a little: "... To the mosue and any smaller animal [gravity] presents practically no dangers. You can drop a mouse down a thousand- yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal's length, breadth, and height each by ten; its weight is reduced to a thousanth, but its surface only to a hundreth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force." The essay goes on to discuss the relative problems of getting wet, being tall, etc. In the case of a squirrel, I suspect that it is able to increase its surface area with flaps of skin, while its weight remains quite low. Bill Pearson
roy@phri.UUCP (Roy Smith) (09/29/88)
There was a study that I saw not too long ago that dealt with the
mortality rate of cats falling over various distances. It showed a
distince maximum at (if I remember correctly) about 5 storys, after which
the rate actually went down significantly (i.e. a cat is more likely to
survive a 20-story drop than a 5-story drop). Unfortunately, I cannot
remember where I saw this. Presumably the study was based on statistical
studies of existing vet case reports, and didn't involve any experimental
procedures. :-)
--
Roy Smith, System Administrator
Public Health Research Institute
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net
"The connector is the network"pell@boulder.Colorado.EDU (Anthony Pelletier) (09/30/88)
In article <3519@phri.UUCP> roy@phri.UUCP (Roy Smith) writes: > > There was a study that I saw not too long ago that dealt with the >mortality rate of cats falling over various distances. It showed a >distince maximum at (if I remember correctly) about 5 storys, after which >the rate actually went down significantly (i.e. a cat is more likely to >survive a 20-story drop than a 5-story drop). Unfortunately, I cannot >remember where I saw this. Presumably the study was based on statistical >Roy Smith, System Administrator I saw this article also, thought my recolection of it is a bit different. I seem to recall 3 stories as the magic height. I believe it was in one of the "thin journals," which, for me, means Science or Nature. But, it is equally likely that I picked up Discover in the Reference room here while trying to avoid working. The vet who had done the compilation of injuries to cats falling out of high appt. buildings postulated that, for the initial part of the fall, the cat treats it like a normal jump, that is, arches its back and stretches its legs towards the ground. He encountered alot of broken legs in this group of a type expected for landing this way. He further postulated that in longer falls, the animal flattens itself out and stretches its legs out parallel to the ground, this increases drag and actually slows the animal down so that, if it falls a few stories farther, it is going slower than if it only fell 3 stories. Again, the injuries (mostly bruises on the underside) were consistent with this. This is not a control study of course. One whould expect the animal rights groups to frown on people tossing kitties out of sky-scrapers. But, if a cat can withstand this type of fall, six feet should be peanuts to a squirrel. -tony
dean@violet.berkeley.edu (Dean Pentcheff) (09/30/88)
In article <3768@boulder.Colorado.EDU> pell@boulder.Colorado.EDU (Anthony Pelletier) writes: .In article <3519@phri.UUCP> roy@phri.UUCP (Roy Smith) writes: .> There was a study that I saw not too long ago that dealt with the .>mortality rate of cats falling over various distances. . .I saw this article also, thought my recolection of it is a bit different. OK, I saw this article also, but I _also_ can't remember where. Does someone have the reference? Please? Thanks. -Dean Dean Pentcheff dean@violet.berkeley.edu To acquire imunity to eloquence is of the utmost importance to the citizens of a democracy. Bertrand Russell
newton@cit-vax.Caltech.Edu (Mike Newton) (09/30/88)
The article everyone is referring to was an AP (?) wire story and ran in many newspapers across the country this summer. - mike -- newton@csvax.caltech.edu amdahl!cit-vax!newton Caltech 256-80 818-356-6771 (afternoons,nights) Pasadena CA 91125 Beach Bums Anonymous, Pasadena President "Reality is a lie that hasn't been found out yet..."
toms@ncifcrf.gov (Tom Schneider) (09/30/88)
In article <8150@cit-vax.Caltech.Edu> newton@cit-vax.UUCP (Mike Newton) writes: >The article everyone is referring to was an AP (?) wire story and ran >in many newspapers across the country this summer. I'm SURE that the original was a 1-2 page article in either Nature or Science sometime in the winter or spring of 1988. I've looked but can't locate it in my files, sorry to report. Tom toms@ncifcrf.gov NO WAIT! IT'S IN MY JOKE FILE!!! @article{Diamond1988, author = "J. M. Diamond", title = "Why cats have nine lives", journal = "Nature", volume = "332", pages = "586-587", year = "1988"} There are other references within. My favorite sentence is: "... a cat falling in the atmosphere reaches a TERMINAL velocity of about 60 m.p.h. ..." &-)
gallaghe@husc8.HARVARD.EDU (Paul Gallagher) (10/01/88)
I saw a television show about squirrels, which showed a squirrel being killed by a fall from a tree (~50 ft.?). Most squirrel nests I've seen are in shorter trees. What's been said about gravity affecting different size organisms differently is fascinating; a bacterium, for example, wouldn't notice gravity at all, but would have to worry about Brownian motion. Richard Lewontin, in his "Dialectical Biologist," arguing against adaptationism in evolutionary biology, argued that there are no general laws to which an organism has to adapt (he phrased it better than me); so, it's a mistake to think of niches somehow preexisting into which organisms must fit. Of course, nothing in the morphology of an organism will violate any laws of mathematics, physics, or chemistry, and it's been a major contribution of people like d'Arcy Thomson and Seilacher to show how these laws are reflected in the form of organisms and the differences among them, but, when considering the entire variety of living things, no particular law can be invoked as an explanation or determining factor for the particular form that this variety takes. This is confusing stuff, and I'm not sure I correctly understand Lewontin, but it seems to me, if true and not just philosophical nit-picking, to be a real challenge to the way many biologists think. Friend of squirrels & glad no longer to be a biology major, Paul Gallagher
jnp@calmasd.GE.COM (John Pantone) (10/01/88)
(Ray Baxter) writes: >(Loren Petrich) writes: >> I once saw a squirrel jump with a drop of over six feet (onto >>a carpeted floor, I might add), and run off as if nothing had >>happened. Is such durability typical of small animals? If so, then it >>would be an outcome of the square-cube law, in which smaller animals >>have a larger drag force (~area~length^2) per unit mass >>(~volume~length^3). >Six feet is not all that far; humans, chimps and large cats can all >handle it. But I take your point, smaller animals, squirrels especially >seem especially graceful about it. It think that adaptation is more >likely to be the cause of this grace than the proportion of drag to mass. I think that F=ma is more likely to be the explanation. The acceleration of gravity is the same for a large and small animal - but their mass is rather dramatically different (by the cube). Small animals simply don't hit with that much force. A dog here in CA recently survived a fall from several stories up a condo - with no ill effects (except, I hope, a better appreciation for heights :-) -- These opinions are solely mine and in no way reflect those of my employer. John M. Pantone @ GE/Calma R&D, 9805 Scranton Rd., San Diego, CA 92121 ...{ucbvax|decvax}!sdcsvax!calmasd!jnp jnp@calmasd.GE.COM GEnie: J.PANTONE
roy@phri.UUCP (Roy Smith) (10/01/88)
newton@cit-vax.UUCP (Mike Newton) writes: > The article everyone is referring to was an AP (?) wire story and ran > in many newspapers across the country this summer. Somebody reminded me that it was probably in Nature or Science, and now that I think about it, I'm pretty sure that's right. I wouldn't be surprised if AP picked it up in one form or another; it's exactly the sort of filler the AP is so good at. -- Roy Smith, System Administrator Public Health Research Institute {allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy@uunet.uu.net "The connector is the network"
papowell@julius.uucp (Patrick Powell) (10/02/88)
In article <414@husc6.harvard.edu> gallaghe@husc8.UUCP (Paul Gallagher) writes: >I saw a television show about squirrels, which showed a squirrel being killed >by a fall from a tree (~50 ft.?). Most squirrel nests I've seen are in >shorter trees. Firstly, most of my observations are based on Big City Squirrels, rather than Country Cousin Squirrels, and my relations with those $%^^& Garden Rats are rather coloured by several decades of trying to keep them out of my garden plot. The original posting asked why squirrels chase each other. They are territorial, and antisocial (or is it "asocial?"), and don't like to share their territories too well. This can even be seen in high food supply areas, such as most University Quads, where the garbage cans provide a more than abundant food supply. Near here, the local red and black squirrels appear to compete quite viciously for nesting sites. I have observed a particular site change possession several times, and have observed several squirrels locked in battle on the ground near it. These fights have led to one squirrel having its tail chewed off, giving it a rather odd appearance. As for falling from heights, I have observed our local squirrels drop 45 feet from a high voltage line to the top of our bird feeder with little if any damage (dammit.). Next year I will try putting a conical hat on it. If they miss, they hit a flagstone patio (or our flowerbed), and appear to be ready for another go at the sunflower seeds. Patrick ("Flying Squirrels? Just what I need") Powell Prof. Patrick Powell, Dept. Computer Science, 136 Lind Hall, 207 Church St. SE, University of Minnesota, Minneapolis, MN 55455 (612)625-3543/625-4002
gillies@p.cs.uiuc.edu (10/03/88)
I recently saw an article (was it in SCIENCE NEWS?) about dropping
cats. It seems that many animals, when given enough time, can orient
themselves for the drop. They splay their arms & legs apart for
maximum wind resistance, and spread their landing over a wide surface
area to minimize the damage.
The article went on to say that this is why cats generally survive
falls of greater than 3 stories, but are often killed in lesser falls.
In a longer fall, the animal has enough time to right itself & prepare
for landing.
Don Gillies, Dept. of Computer Science, University of Illinois
1304 W. Springfield, Urbana, Ill 61801
ARPA: gillies@cs.uiuc.edu UUCP: {uunet,ihnp4,harvard}!uiucdcs!gilliesosa845b@vaxc.cc.monash.edu.au (Monash radio 3MU) (10/03/88)
The article everyone is referring to about dropping cats from 5 storeys where the mortality rate actually decreased above 5 storeys I also have read, and I don't think it was in Nature or Science but in a recent issue of Discover. (We subscribe to Discover at my joint, so we read it and I distinctly remember it being in there in a 'latest news' type section, I believe.) As to the exact issue, I don't know at the moment. Anyway, I hope this helps. Dien Rice Monash University (Melb., Australia) (student)
quis@cs.qmc.ac.uk (Chris Rose) (10/06/88)
I believe that the article Appeared in Scientific American (If I remember correctly it featured pictures of rather worried looking moggies in various stages of flight.) Apologies that I do not have a issue reference, I will look it up. Chris Rose
toms@ncifcrf.gov (Tom Schneider) (10/19/88)
In article <14847@agate.BERKELEY.EDU> dean@violet.berkeley.edu (Dean Pentcheff) writes: >In article <3768@boulder.Colorado.EDU> pell@boulder.Colorado.EDU (Anthony Pelletier) writes: >.In article <3519@phri.UUCP> roy@phri.UUCP (Roy Smith) writes: >.> There was a study that I saw not too long ago that dealt with the >.>mortality rate of cats falling over various distances. >. >.I saw this article also, thought my recolection of it is a bit different. > >OK, I saw this article also, but I _also_ can't remember where. Does >someone have the reference? Please? > >Dean Pentcheff dean@violet.berkeley.edu > >To acquire imunity to eloquence is of the utmost importance to the >citizens of a democracy. Bertrand Russell Looks like many people didn't get my previous posting on this! An original source is in Nature, it gives other references: @article{Diamond1988, author = "J. M. Diamond", title = "Why cats have nine lives", journal = "Nature", volume = "332", pages = "586-587", year = "1988"} Tom Schneider National Cancer Institute Laboratory of Mathematical Biology Frederick, Maryland toms@ncifcrf.gov