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Gray Squirrels Often Endure Mange Outbreaks During Winter

Writer's picture: Patrick DurkinPatrick Durkin

   Judging by their ample girths, the gray squirrels in my backyard eat much and exercise little.


   In fact, when glancing out the window here in Eau Claire, it’s common to do double-takes when seeing a squirrel gnawing on sunflower seeds while resting on its haunches. Though you know it’s a gray squirrel, you must assure yourself it’s not a distant cousin, the groundhog.


   That’s no exaggeration. If you put a seesaw on our patio, and strapped a young groundhog on one end and a portly gray squirrel on the other, you could take wagers on how the teetertotter would tilt.


  Using only the eyeball test, our scurry of squirrels looks robust and healthy; even diverse. (Yes, a “scurry” is the term for a group of squirrels.) Most of our squirrels wear the species’ customary gray coat, but others dress in black, white or off-white coats. One even wore black pants with a gray blazer, but he’s long gone, as is a squirrel with no tail.


   Given our squirrels’ apparent good health, we grew concerned this winter when about half started sporting bare or balding backs and upper chests. Their exposed skin often looks like dark leather, while other bald spots are pink with bloody scabs. Whatever the cause, it doesn’t curb their appetites or make them timid. They still eat endlessly and chase their inferiors when annoyed.

Gray squirrels with mange often lose patches of hair, and then self-inflict wounds by scratching the itchy area. Mange occurs and spreads often in winter when squirrels huddle together in mite-infested nests inside den trees.   — Patrick Durkin photos

   Online searches suggest our squirrels might be suffering from “notoedric mange,” which is caused by a burrowing mite. Information from the Illinois Department of Natural Resources reads:


   “Notoedric mange can be transmitted squirrel to squirrel. It causes large patches of fur to fall out and the skin to become dark and thick. You might also see scabs on the squirrel’s skin, because they scratch themselves to relieve the itching caused by mites. Squirrels often fully recover from mange, although those with severe fur loss might not survive cold winters.”


   Further, no one has documented squirrel mange spreading to dogs or cats.


   Because I’ve learned to distrust Dr. Google after misdiagnosing my own aches and pains, I sought an expert’s independent verification of mange in our squirrels. That meant sending photos of our afflicted squirrels to the “Squirrel Doctor,” John L. Koprowski at the University of Wyoming.


   Koprowski, a mammalogist, is dean and professor in U-Wyoming’s department of zoology and physiology. Just as important, Koprowski has a Ph.D. in “all things squirrel,” and has twice shared his extensive expertise as a guest on the popular MeatEater Podcast Network.


   The Squirrel Doctor answered promptly after receiving my photos. He wrote:


   “These look like mange, and it may very well continue to get worse. Outbreaks are often localized. Usually, when you see one case, more will follow, perhaps especially in eastern gray squirrels because they tend to nest in large groups and the parasites — a burrowing skin mite — are easily spread.”


   Koprowski also said mange outbreaks seem more common in winter when tree squirrels spend much time intertwined in cramped dens to stay warm.


   “Squirrels nest in larger groups during winter,” Koprowski wrote. “They have thick winter pelage, and often use fewer nests or tree cavities, where their bedding builds up larger ectoparasite populations. The mites burrow into the skin, and larger populations cause more hair loss, some flaking and roughing of the skin, occasionally a bit of oozing, and after scratching, potential open sores.”


   I know what you’re thinking: “How many squirrels spoon together inside a tree den?”


   The Squirrel Doctor has studied that. A research report Koprowski published in 1996 found that gray squirrels commonly nest in groups of two to nine per den, with the largest groups cohabitating in autumn and winter.


   Further, though it has nothing to do with mange or how it spreads, Koprowski’s 1996 study also found that unrelated adult male gray squirrels often nest together. And although unrelated female gray squirrels commonly share nests/dens, they’re most friendly to closely related females within their kin groups.


   The thought of all these squirrels setting aside their petty differences to cuddle against the cold sounds surprising. After all, every time most of us see or hear squirrels, they’re barking at some squatter or chasing each other across the lawn or up a tree. Then again, our assumptions might be skewed, given that we’re more likely to notice hostile encounters between squirrels.


   Plus, it’s hard to test our assumptions. I mean, who marks a bunch of squirrels with a cold-branding iron to identify individuals by gender and approximate age, and then watches them for four years, recording their interactions as friendly or hostile?


   Pfft!


   The Squirrel Doctor, that’s who. If you don’t believe it, read his 13-page research paper, titled, “Natal Philopatry, Communal Nesting, and Kinship in Fox Squirrels and Gray Squirrels.”


   Of the 900 interactions Koprowski witnessed between his cryogenically branded adult gray squirrels from May 1986 through May 1990, he recorded 556 (62%) as hostile. He broke it down even further: Of the 305 male-female interactions Koprowski witnessed, 202 (66%) led to hostilities. Of the 314 male-male interactions he witnessed, 170 (54%) caused hostilities. And of the 281 female-female interactions he watched, 184 (65.5%) were unfriendly.


   And yet, when winter demands gray squirrels conserve calories and huddle for warmth, they set aside their differences, and tolerate each other’s annoying habits and questionable hygiene.


   Humans, of course, can’t trust nature to let squirrels handle things. Folks often ask wildlife agencies and academicians if “someone” should give squirrels antibiotic pills, spray them with permethrin, or wash them with mite-killing shampoos.


   No. Even if we could schedule squirrels for such treatments and make them show up, they’d just go home to the same mite-infected nest or den and get mange again.


   It’s all they know, after all. And if it was good enough for their ancestors, it’s good enough for them.


 


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