[NatureNS] beaver size new gnawledge

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Date: Wed, 24 Sep 2008 22:23:26 -0300
From: "Ronald Arsenault" <rongarsenault@gmail.com>
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Hello Steve, Dave and others,

As everybody seems to be in a confession mode....

I made an assumption that may be erroneous should Dave's suggestion be
correct.  It is actually the gnaw marks of an adult beaver which measure
approximately 6 mm in width.  I assumed a this represented the width of the
teeth of an adult beaver.  If Dave's suggestion that the width of the gnaw
marks represent 2/3 of the width of the incisor teeth is correct, then an
adult beaver would have incisors 9 mm wide.  Dave, is the skull you have
that of an adult beaver?

However, the above does not change my initial conclusions that the evidence
still strongly points to a beaver (the presence of muskrats does not exclude
beaver) and that the beaver responsible for the cutting was likely a sub
adult.

Ron

2008/9/24 Steve Shaw <srshaw@dal.ca>

> Hi Dave and others,
> No Dave, your note didn't come through on NNS, only the recent one direct
> to me.  One of my earlier 2 posts came through in the wrong order, though,
> and NNS has seemed erratic or slow sometimes, recently, as others have
> noted.
>
> Yes, you caught me with an inexcusable error when I converted 3.75 mm to
> 5/64 inch (thinking that some out there may not like millimeters) when it
> should have read approximately 5/32 inch.  Actually I missed this error
> because I didn't convert it arithmetically but stuck a ruler next to two
> lines I'd drawn, and mis-read 32ths as 64ths on the ruler.  ( No, I'm not
> the guy who designed the lens in Imperial for the Hubble telescope which was
> then made in metric units, or was it the other way round?).   However and in
> consequence, I'm VERY glad to find that you made complimentary (admittedly
> smaller) error:  3.75 mm is actually IS a little bit larger  than 1/8 inch,
> not smaller -- I make it 1.181 eighths-of-an-inch if you want to get fancy.
>
> To be serious, your reply is useful because it helps to clarify my original
> short post on this beaver size thing, which may have been well-intended but
> was a really ill-conceived as written, I've realized since.   The round
> alder branches were gnawed at a shallow angle, so the en face view of the
> cut was roughly elliptical, with the long axis of the ellipse in line with
> the branch.  The branch and the long axis of the cut would actually have
> been parallel to the axis of the beaver's body as it stood up in the lake to
> gnaw away.  But the 8 or so gnaw marks that I measured as 3.75 mm each, ran
> ACROSS the ellipse (i.e. parallel to the short minor axis of it).  This
> would have been orthogonal to (at right angles to) the beaver's incisors,
> not parallel with them!   It then makes no sense to ask (as I did) how wide
> the teeth are in a beaver of a certain age in relation to these cuts:  the
> marks will not be related to tooth width, but to the depth of each of the 8
> chisel-cuts it made in lopping off the branch, as you correctly point out.
> So the question should be reformulated to ask how long or deep is each of
> the series of chisel-cuts made by a beaver of a certain age or size,
> probably harder to assess accurately.   From Ron Arsenault's reply that the
> teeth on an adult are about 6 mm wide which agrees with your specimen, it
> sounds like you may have an adult beaver skull in your possession.  If your
> estimate of a cut-depth of 3.4 mm for such a beast is realistic, "ours" then
> could have been a pretty large beaver.
>
> I also put the local observations round an e-mail list for people who live
> on Chocolate Lake here, and a few replies revealed that a muskrat called
> Charlie lives under a neighbour's dock, eats his irises and hostas and has
> even been seen swimming back home with lake vegetation in its mouth.  This
> has prompted humorous bets which so far rate the likely identification of
> the culprit as muskrats 2, beavers 1 (I'm the '1'), but no-one has seen the
> muskrat eating woody stuff including alders, and these are mostly townies
> whose opinions may not be reliable as those of folk who actually know about
> beavers, to put it mildly.  The clincher may be a third hand report from a
> few days ago that a workman actually observed a beaver swimming towards the
> water inlet pipe for the lake with a bundle of sticks, and my bet is firmly
> on a beaver.   If correct, we may be about to experience a drop in lake
> level that has little to do with global climate change.
> Steve
>
>  *****************************************
> On 24-Sep-08, at 2:15 PM, David & Alison Webster wrote:
>
> Hi Steve.            Sept 23. 2008
>>   I sent this yesterday to Naturens but for some reason it didn't get
>> through so will send it offline to supplement your fund of gnawledge,
>> especially beaver gnawledge.
>>   Also I notice that I said 3.4 mm apart when I intended to say 3.4 mm
>> wide, i.e. ridges 3.4 mm wide (& ~ 4.00 mm apart).
>> And that 1/8' was intended to be 1/8"
>> Yt, DW
>>
>> -------- Original Message --------
>> Subject: Re: [NatureNS] beaver - size estimation
>> Date: Mon, 22 Sep 2008 12:10:41 -0300
>> From: David & Alison Webster <dwebster@glinx.com>
>> To: naturens@chebucto.ns.ca
>> References: <BE20011C928B4CC38A2D1CEBD6F14ABF@bernard> <
>> 50035.216.118.137.234.1222010582.squirrel@webmail.seaside.ns.ca> <
>> 20080921185446.h82rrgkcqvusococ@my4.dal.ca>
>>
>> Hi Steve & All,                Sept 22, 2008
>>   The incisor teeth of a beaver skull, that I happen to have, are 6 mm
>> wide at the cutting edge and are spaced 1.4 mm apart. The teeth have a
>> curved face like a gouge  (1/4" #7 spoon gouge as shown in Lee Valley) and
>> to avoid torn wood, buried teeth, splinters between teeth, shavings that
>> don't curl well, damaged cutting edges etc a wise beaver would never cut to
>> the full depth of the curve (i.e. full width of the cutting edge) and likely
>> would seldom use more than 2/3 of the cutting edge.
>>
>>   Thus this beaver would likely have left ~parallel ridges of wood at
>> least 3.4 mm apart so this fits your 3.75 mm well.
>>
>>     BTW 3.75 mm is less than 1/8' and 4 x 8 =32 not 64 :>).
>> Yt, DW
>>
>> Stephen Shaw wrote:
>>
>>> Hi again Billy, or anyone else,
>>> As an afterthought on a recent reply from me about this, could an
>>> experienced
>>> woodsman tell the approximate size of the beast from the spacing of its
>>> gnaw
>>> marks?  Somebody must have looked into this in