Beaver Tale, Unexpected Consequences

[From Hank Folson (930130)]

I saw the world record beaver lodge (25' high) in northern Manitoba after
the pond it was in had been drained to make way for a new railroad line. I
still remember that the stream was bordered by rock, and where the dam had
been was very narrow, so the beaver could add to the height without a
great deal of effort. I suspect that whatever beavers' reference levels
for dam building are, the geography here led to a very deep pond being
easily built, and so the world's tallest beaver house was built.

I notice in charts showing the aspects of a control system, there is often
a box marked "Unexpected Consequences". I don't think this beaver wanted
to build the world's largest beaver lodge, but was just controlling for
whatever beavers control for, and this huge house was just an unexpected
consequence of building where he built. A lot of the observations quoted
in Greg's post are really just unexpected consequences of a control system

As to half girdled trees, I wonder if the beaver is trying to ensure a
supply of readily available material for repairing damn dam damage? Just
cutting down trees to have for repairs will not work, as the trees will
quickly rot and be useless. By half cutting them, the trees stay upright,
yet can felled in a hurry should the dam break, allowing water to escape
and exposing the lodge to predators. This of course is not as romantic and
selfless as the quote Greg posted, but may be better control theory. It
would be interesting to see if there is any correlation between number of
half-girdled trees and the size of the dam. I agree intuitively with Bill
that half girdled trees won't be found during dam construction.

Back in my days of believing in instincts, I was fascinated that if a
beaver has created about a 10' deep pond, it will have about 5 dams along
the stream, each providing about a 2' increase in water level. Thus the
failure of any dam results in only a 2' lowering of water level. In
addition, each dam sees only the net loading of 2' of water, making
construction much less critical than a single dam with a 10' head of water
I have no idea how the beaver figures this all out. Beavers with goals for
a series of small dams might survive better, per Darwin, than beavers that
build one big monster dam. Or it may simply be that with their limited
capabilities, beavers can't construct a dam to hold more than so many feet
of water reliably. Perhaps it is as simple as having a program of building
2' high dams. Then if the pond depth does not satisfy some reference
level, another dam is built upstream to raise the level another 2', and
so on until the reference level for pond depth is satisfied. Not very
romantic, but then neither are orange colored teeth (to non-beavers).

Has anyone ever tried to get naturalists interested in PCT? Most nature
films, books and TV programs I have seen rely pretty heavily on a
combination of romance and educated guesses based on observations from
the external viewers' point of view, not the furry little control system's.

Hank Folson
Henry James Bicycles, Inc. 704 Elvira Avenue, Redondo Beach, CA 90277
310-540-1552 (Day & Eve.) MCI MAIL: 509-6370 Internet: 5096370@MCIMAIL.COM