RODENTS and HARES

Under construction May 2011

RODENTS AND HARES

Collared Pika, Snowshoe Hare, and Alaskan Hare are not rodents, but are small prey animals and are grouped here for convenience. 

ORDER RODENTIA (the rodents)

Alaska Marmot (Marmota broweri)

Arctic Ground Squirrel (Spermophilus parryii)

Beaver (Castor canadensis)

Hoary Marmot (Marmota caligata)

Muskrat (Ondatra zibethicus)

Northern Flying Squirrel (Glaucomys sabrinus yukonensis)

Porcupine (Erethizon dorsatum)

Raccoon (Proycon lotor)

Red Squirrel (Tamiasciurus hudsonicus)

Woodchuck (Marmota monax)

LENGTH: Length of guard hairs for the rodents is not especially useful except for the squirrels (Arctic Ground, Northern Flying and Red) who have shorter guard hairs than the other rodents observed, with a length not exceeding 30mm except on the tail where it might reach 35mm on the arctic ground squirrel and 45 mm on the red squirrel.  Rodent hairs longer than an inch are rare according to Brown (1942)

WIDTH: Maximum width of the guard hair is not a useful clue because of wide and overlapping variation.  Exception may be porcupines and perhaps beavers who are the only rodents with width measured over 100 microns on some samples.  Rodent guard hair does not usually feature the overall shield shape seen on weasels, where the guard hair has a long narrow stalk and then a broad paddle shape near the tip.  Marmots and muskrats can have a wide pigmented shield-like section and then a thinner, less-pigmented area leading to the base.

MEDULLA: Usually have a prominent compound medulla (Mayer 1952)  Between the marmots, it seems the Alaska marmot has a long tapering tip without a medulla, while the Hoary has a more abrupt taper with the medulla extending almost to the end. Medulla of rodents is often heavily pigmented and has a dark or mottled dark-light look with features difficult to distinguish.  A tire-tread shaped medulla with bumpy edges and fingers of cortex extending into the medulla is found on the muskrat and squirrel guard hairs (although on the squirrels you need to look in the lighter-colored bands.)

MEDULLARY INDEX: Medullary index in the rodents tends to be 0.6 to 0.9, and a narrower medulla might be a useful clue for the beaver and the raccoon, whose medullas are in the 0.3 to 0.4 range.

SCALE: The typical cuticle scale pattern on rodent guard hairs tends to have large puzzle-piece like ovals near the base, which can form diagonals going in different directions and are only two or three scales across in microscopic view.  These scale margins gradually become more irregular and jagged with serrated edges, usually becoming closer and closer together near the tip.  This is distinguished from the weasels, which have a region of pointy diamond petal shaped scales between the smooth puzzle pieces of the base and the closely spaced jagged-edged scales near the tip.  The scale pattern is not especially useful in determining which rodent you have, although it seems the porcupine may have no change in the scale pattern along the length of the shaft, with raggedy edged scales remaining widely spaced for the whole length?  The muskrat seems to have less jaggedness to the margins, often forming scalloped shaped instead which may be a clue.  This more gently scalloped edge also appears a bit on the red squirrel scale pattern. 

UNDERFUR: Underfur length under 15mm suggests either muskrat or one of the squirrels.  Marmot underfur tends to be long, over 50mm.  Underfur width is under 20 microns for the squirrels, the beaver and the muskrat.  Lack of medulla in the underfur is unusual among the Alaskan rodents studied.  It can happen in the muskrat, raccoon and the Arctic ground squirrel, and perhaps occasionally in red squirrel.  On the other hand, a complicated medulla in the underfur may help ID porcupine, who has a wide medulla with lots of pigment, although beware: the porcupine underfur may have a very long tapering tip with no medulla.  Underfur of squirrels also may have a distinct brownish tip after a seemingly colorless shaft for most of its length.  Squirrels may also have intermediate sized hairs with long narrow interrupted or uniserial ladder medulla near the base until the shield where the medulla looks like tire tread.  Distinguishing among the squirrels: Arctic ground squirrel underfur has no medulla.  Northern flying squirrel is gray in color?  To distinguish squirrel from muskrat, observe the underfur.  Often, muskrat underfur has a gray appearance to the naked eye with a hint of cool lavender purple.  Under magnification, the muskrat underfur often has no medulla, or a few fibers will have an interrupted medulla.  The underfur is also an important clue for raccoon.  In some samples there is no medulla, and in others the medulla is very interrupted if it appears at all.  The scale pattern of the raccoon underfur has a prominent spiky pinecone look as well.

COLOR:  Beaver guard hair often has a golden yellow (almost glowing) appearance to the cortex, and the medulla may be interrupted.   Unfortunately, the guard hair is sometimes plucked or sheared from beaver fur when used on artifacts, garments and the like.  Banding is common in rodents.  Raccoon has distinctly banded guard hair, white near the base, then a brown band, and then a light tip.  Porcupine, marmot, woodchuck and Arctic ground squirrel are also banded.

SUMMARY:  Rodents have considerable variation and overlap in many features and a combination of clues is needed for secure identification.

ORDER LAGOMORPHA (the lagomorphs)

Alaskan Hare/ Tundra Hare (Lepus othus)

Collared Pika (Ochotona collaris)

Snowshoe Hare/ Varying Hare (Lepus americanus)

LENGTH: All have maximum lengths in the 30-50mm range.

WIDTH: Pika is narrower, with a maximum of 55 microns while the hares are often twice that width, around 75-100 microns.

MEDULLA: Medulla in hares has a very distinct rectangular ladder like cell pattern that resembles kernels on a corn cob.  This is diagnostic for rabbits and hares.  Pika medulla is more zipper-like.  There may be more rows across the medulla on the Snowshoe hare, but we need more samples to know for certain.

MEDULLARY INDEX: All are in the 0.8 range.

SCALE: The scale pattern on the hares is similar: on the long narrower section of the shaft near the base, there are very long V-shaped pointy petals whose sides are not straight but wavy, giving a sort of elongated flame-like look.  Some of these are nested in each other like chevrons.  Pika scale is distinct, with comb-like margins on the scales, looking like crowns with long blunt tines.

UNDERFUR: There is not enough variation in the underfur of pikas and hares to make useful distinctions.

COLOR: Not especially helpful

SUMMARY: The corncob look of the medulla and extreme diagonal chevrons of the scale on the guard hairs are a slam-dunk combination for hares, although distinguishing between Snowshow and Alaska is tricky.  We need more sample to pin that down, since our Alaska hare sample was probably not from the longest densest fur of the animal.

Images upcoming

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