The food-wood above the first dam being cut off,
they move down stream; for the beaver always cuts on the banks above
his dam, and lets the current work for him in transportation.
Sometimes, when the banks are such that a pond cannot be made, three
or four dams will be built close together, the back-water of one
reaching up to the one above, like a series of locks on a canal. This
is to keep the colony together, and yet give room for play and
storage.
There is the greatest difference of opinion as to the intelligence
displayed by the beavers in choosing a site for their dam, one
observer claiming skill, ingenuity, even reason for the beavers;
another claiming a mere instinctive haphazard piling together of
materials anywhere in the stream. I have seen perhaps a hundred
different dams in the wilderness, nearly all of which were well
placed. Occasionally I have found one that looked like a stupid piece
of work--two or three hundred feet of alder brush and gravel across
the widest part of a stream, when, by building just above or below, a
dam one-fourth the length might have given them better water. This
must be said, however, for the builders, that perhaps they found a
better soil for digging their tunnels, or a more convenient spot for
their houses near their own dam; or that they knew what they wanted
better than their critic did.
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