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From: wrp@biochsn.acc.virginia.edu (William R. Pearson)
Newsgroups: sci.bio
Subject: Re: Squirrel Questions
Message-ID: <595@hudson.acc.virginia.edu>
Date: 29 Sep 88 13:12:01 GMT
References: <22811@mordor.s1.gov> <4150@polya.Stanford.EDU>
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Reply-To: wrp@biochsn.acc.Virginia.EDU (William R. Pearson)
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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