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Squirrel
Study Skins
Abstract.
Sherman’s Fox Squirrel, Sciurus niger
shermani, and the gray squirrel, Sciurus
carolinensis, were collected as road kills from White Oak Plantation, in
Northeast Florida. Study skins were
completed on two Sciurus niger shermani and
one Sciurus carolinensis.
The study skins will provide a helpful tool in future studies of these
squirrels. Study skins provide an
opportunity to collect data such as sex ratios, weight versus length ratios and
future studies of information which can be gathered from the skins on their
tags. The technique for
preparing the study skins has been developed and described here.
The same methods used to prepare squirrel study skins can be applied to
most small mammals. A mink is used
as an example in the following list of procedures. (fig. 1)
Materials
and Methods
Step
1: Measurements
-measure the mass of the squirrel in grams.
-measure
the total length of the squirrel from the tip of the true tail (where the bone
and
muscle stop- not the fur) to the tip of the nose in millimeters (mm).
-measure
the length of the tail in mm.
-measure
the length of the back or hind foot (from the point where the foot meets the leg
to the end of the middle toe
in mm.
-measure
the length of the ear from the ear notch to the tip of the ear in mm.
-identify
the sex of the squirrel, male or female, and species, (information on the place
and date of collection should also be recorded.
-if
the sex is male, measure testis length.
-if
sex is female, check for embryos and record number and size if present.
-cornmeal
may be used thruoughout the process as a means of absorbing blood and other
fluids by rubbing it gently into the hair (Hall, p.16; fig. 2).
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(Figure
1) A mink is used as demonstration of
study skin procedures.
The same procedures may be used for most small mammals. (Figure
2)
Corrnmeal
is used to absorb excess moisture of the animal
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start skinning on the ventral side. Turn
the squirrel on its back and begin pulling a fold skin
on the ventral side away from the muscle.
-make
a small incision on its belly, parallel to the spine, cutting only the skin, not
the muscle. Keep the first incision straight and just long enough to allow
extraction of the animal body.
(Figure
3) The first incision on the belly of the mammal
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(Figure
4) The separation of the skin from the muscle
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(Figure
5) Skin
is loosened around dorsal and ventral sides of mammal
-with
your fingers begin to separate the squirrel skin from the muscle on the belly or
ventral side. Work your way around
the dorsal side of the squirrel. (Remember,
only one incision has been made). Incisions and any holes in the skin should be kept to a
minimum because they will need to be sewn up later. (Figures 4-5)
Step
3: Skinning the hind legs
(Figure
6) Working
to skin the hind legs, and cutting the bone of the leg.
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-once
the squirrel skin has been separated on the ventral and dorsal sides around the
mid section, you can begin working toward the hind legs.
Separate the skin from the muscle around the top portion of a leg.
Then, take the leg by the paw and put pressure on the leg to push it
towards the inside of the squirrel skin, (Turning
it inside out). (Figure 6)
-you
will not be able to turn the leg completely inside out.
Cease forcing the leg through when you reach the beginning of the paw
pad. Cut the leg off, from inside
the skin at the point just before the paw (Be sure not to cut through any skin)
(Figure 6).
-repeat
the same procedure for the other hind leg.
-then,
cut through the colon immediately posterior to the anus to separate the
intestinal tract from the skin.
Step
4: Tail
-to
remove the tail, separate it from the skin at the base.
Apply pressure by tugging at the base of the tail with one hand and
holding the edge of the skin of the tail with the tips of your fingers of the
other hand. (Figures 7, 8)
-be
careful in this step not to remove any fur.
-remember
the purpose is to separate the muscle from the skin of the tail.
-this
is somewhat difficult, so persistance and carefulness is the key.
Once the muscular tail starts to come out, it will pull out the rest of
the way more easily.
-if
there is difficulty in pulling the skin away from the tail, try cutting the
connective tissues holding the skin to the tail.
This will take longer, but it will keep you from pulling out fur or
breaking the tail(Booth, p.26)
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Figure
7 Figure
8
Step
5: Front Legs
-once
the tail is skinned, use the same procedure for the two front legs as used for
the hind legs.
Step
6: Skinning the head
-now it is time to skin the head. This
is slower work than the rest of the body. You
may
want
to use an instrument with a partially rounded end to separate the skin from the
muscles around the head. (Figures
9,10)
-when
you get to the ears, then cut next to the skull through the skin of the external
auditory membrane. (If done
corretly, no sewing will need to be done) (Booth, p.27).
-the
same procedure will be used around the eyes as around the ears.
(Be sure to leave the eyelids intact with the skin).
-continue
this procedure around the mouth and nose, and the skinning portion will be
completed. (Figures 11, 12)
(Figure
10) Retain
eyelids with skin (Figure
9) Slowly
remove skin from skull using scalpal or blunt object
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(Figure
11) Skinned
mink—ventral side (Figure
12) Skinned
Mink—dorsal side
Step
7: Finishing Touches
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-use
corn meal to clean fluids from the skin. Next, use borax on the other side of the skin by rubbing, to
dry and sterilize the skin. Retain
the body of the squirrel until you have determined sex, length of testis, and/or
presence of embryos. Remove excess
muscle tissue
from
skin. (Figure 13)
Figure
14 Figure
13
-cut
wire supports for the four legs and the tail.
These should extend from the paw pad or end of the tail to the middle of
the body. Wrap cotton around one
end of a piece of wire for the tail. The
wire should extend to the middle of the squirrel skin once it is pushed to the
end of the tail and should be placed on the ventral side of the cotton body.
(Figure 14)
-wrap
cotton around the wire for the legs of the squirrel push the wire down the skin
of the leg. When you reach the last
joint, push through it to the end of the paw, do not punture the paw skin.
The wire should extend past the leg to the middle of the body on the
inside. Repeat step for other three legs. Leg
wires should be placed on the ventral side of the cotton body as well.
(Figure 15)
Figure
15
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-form
a cotton body and place it inside the squirrels skin.
(Figures 16, 17)
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-suture
the initial incision to close.
Figure
16 Figure
17
-place
on a piece of cardboard and pin the paws in the desired position to dry.
(Usually, the front legs are extended toward the anterior end of the squirrel
close to the head with paws facing down. The hind legs are extended straight back near the tail facing
up) (Figure 18). One of the
preferred methods is to properly line up the tail-wire, making sure that it is
paralle with the leg wires “and on the mindline of the belly mid-way between
the wires of the two hind legs.” (Hall, p. 20)
-use
formaldyhyde to preserve the paws by injection with a hypodermic needle.
To preserve the nose and ears place the needle inside a nostril or ear
and squeeze a few drops of formaldyhyde into them .
(Figure
18) Previously
completed study skins. Two
fox squirrels (Sciurus niger shermani) One grey
squirrel (Sciurus carolinenisis)
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-fill
in an identification tag with appropriate data. (Include the lengths in (mm),of
thetotal length, tail length, hind foot length, and ear notch length(fig.
19) Include the weight in
grams, the sex (testis length if male, number and size of embryos if present),
date of collection and the location, who collected it, and who prepared the
study skin with the date of preperation) It
is extremely important to label a speciman.
You can not record enough data on a study skin—be as specific as
possible. (Booth, p. 23)
Booth,
Ernest S. (1961).
How to Know the Mammals. Dubuque,
Iowa: WM. C. Brown.
Hall,
E. Raymond. (1962).
Collecting and Preparing Study Specimans of Vertebrates.
Lawerence, Kansas: University of Kansas.
