What is a White Squirrel?

Lions and Tigers and … White Squirrels?

Just what is a white squirrel, anyway? Is it a distinct species? Is it a mutation? These are some of my most FAQs. And the answer is ……. it depends. There is, in fact, one tree squirrel for which a white coat seems to be a characteristic of the entire species, at least in parts of its distribution. Its an Oriental Tree Squirrel of the genus Callosciurus (Callosciurus translates as “beautiful squirrel”) found in Thailand and other parts of South East Asia (Thorington and Ferrel, 2006).  Another belongs to a yet undescribed species recently found on Palawan Island in the Philippines and thought to be endangered (for more information click here).  So if you sighted a white squirrel here in North America outside of captivity, its almost certainly a color variant of one of our native species of the genus Sciurus (only distantly related to Callosciurus*). In my neighborhood, that would be the Eastern Gray Squirrel (Sciurus carolinensis). Most of what follows will be in reference to that species but white coated Fox Squirrels and Red Squirrels have been sighted, as well.  Note: this posting becomes increasingly technical as it progresses, comparing the possible mechanisms by which different variants may arise; if such mechanisms are not of interest to you, I think you may want to skip down and read the last three paragraphs which focus on white squirrels, again, and are, I hope, of general interest.

There is much variation in squirrel coat color both locally and regionally. The general pattern of brown/gray on top and white below (counter shading)  is considered the wild type from which other variations arose. These wild types, like most mammals, have dark eyes. The brown, reddish, gray, or even black color comes from the production of a pigment called melanin which, itself, comes in at least two varieties, eumelanin (black/brown) and phaeomelanin (red/yellow). Different combinations and arrangements of these two pigments produces a variety of hues.  Alternating between one or the other (or neither) results in banded hairs referred to as agouti. All this variation can arise from change in either the genes that control the production and packaging of melanin itself, or of genes that control the distribution of melanin production. After all, most wild type gray squirrels have a white abdomen not because there are mutated genes in those cells but because there are regulatory genes which suppress the activity of melanin genes in these locations but not others (or prevent melanin producing cells called melanocytes from reaching such regions as discussed below). The white abdomen is adaptive. It makes the squirrel less visible from below against a light sky. Yet some squirrels have tan or ochre bellies (witness the now infamous Stan the rally squirrel for the 2011 St. Louis Cardinals’).  Black or melanistic squirrels produce excessive amounts of melanin in comparison to the wild type and in expanded regions of the body. These variants are often found at higher latitudes and the dark color is thought to be involved in thermoregulation. The point I am making here is that while variation from wild type comes about by genetic change known as mutation, the word mutation carries a negative connotation, implying a freakish condition. In this case it produces a wealth of variation that may actually be appropriate for local conditions (including human preference). Thus, I prefer the term variant over mutant although I will use both below for variety.

With that said, white squirrels are just another color variant of this very variable species. The most common sightings of white squirrels are of isolated individuals with a completely white coat but dark eyes, a condition known as leucistic. This variant (illustrated on the left) appears to spring up sporadically all over the species’ range and then dies out, only to pop up again somewhere else (see list of colonies and sighting). I think these are spontaneous mutants of some gene that delegates the use of the pigment (melanin) gene, not mutants of the melanin gene itself ( possible mechanism is suggested below). Instead of being produced in skin/hair cells and the eyes, it is only produced in the eyes. In another mutation, one in the genes that are directly responsible for producing melanin, no cells make the pigment and the squirrel is not only white but has pink or blue eyes. These true “albinos” are reported even less commonly, probably because without the eye pigment to reduce glare, their vision is impaired and they may suffer more from falls.  Increased predation may also be a factor; a decline in the well monitored Olney Illinois albino population has been linked to cats.

Still rarer seems to be the type of coat pattern we have here in Brevard NC. The coat is mostly white but there is a distinctive head patch and dorsal stripe that broadens in the shoulder region. The head patch can be solid, horseshoe or doughnut shaped; it may resemble a triangle, a diamond, deer tracks or even a widow’s peak (Count Dracula). There is some evidence that this pattern is inherited (Burgin: Inheritance of Head Patch).  Although there is much variation in the amount of pigmentation, these white squirrels definitely can produce melanin, not just in the eyes but in hair cells as well. I’m guessing but I think the gene responsible is probably what we call a regulator gene, effecting the distribution of hair color, not color itself (although agouti and red hairs seem to be lacking). The region of white hair, normally restricted to the abdomen in a gray squirrel, is expanded at the expense of pigmented regions. A simple mechanism by which this might arise is from a shortage of melanocytes, the melanin producing cells (Dalzell, 1997).  Melanocytes do not originate in the skin.  Early in embryonic development, they are part of the neural crest which pinches off from the neural tube as it is about to close.  These cells then migrate throughout the body where they contribute to the formation of many structures, most of which are much more vital to survival than coat color (a complete lack of neural crest cells would be lethal).  Those destined to form melanocytes are called melanoblasts when immature.  Their role at this stage is not to produce melanin but to migrate to the germative layers of the skin and penetrate into developing hair follicles.   Another important function is to proliferate along the way.  From a few dozen original cells, they will end up forming millions of mature, melanin producing melanocytes.  But if something were to impede their replication, their numbers might not be sufficient to supply the entire body.  Since, as mentioned above, counter shading is adaptive, we would expect the back (dorsal) areas to have priority to this limited supply.  In fact, melanoblasts begin their journey in close proximity to this region of the body which would thereby get “first crack” at them, anyway.  Simply retaining them near their point of origin would result in what appears to be an extended white “abdominal” region, i.e., a Brevard white squirrel!  I have argued elsewhere (“Inheritance: Dominant or Recessive?”) that this predisposition to express the white pattern is inherited in accordance to a dominant model.

Albino squirrels appear to have a normal abundance and distribution of melanocytes; they just can’t produce melanin, period, skin or eyes; the subcellular structures where melanin is typically stored are empty (Searle, 1968).   The leucistic condition can also be explained by interference in the normal develpment of these pigment producing cells.  As they migrate and take up residence in the skin, the melanoblasts remain immature non-pigment producing cells.  Normally they are destined to become mature pigment producing melanocytes under the influence of chemicals secreted by surrounding cells in the skin (fibroblasts and keratinocytes).  Mutations are known (Wolpert et al, 1998:298) where these chemical inducers are altered or not recognized by the melanoblasts which remain immature (and thereby pigmentless) for life.  Since this occurs locally in the skin after migration, it would not effect the normal induction of melanin production in the eyes.  Variants that result from the lack of a receptor or chemical inducer, like those that result from non-functional enzymes as in albinos, are usually recessive.  That is, all it takes is one normal version of the gene responsible and the wild type would be produced.  The unusual variant, in this case leucistic, probably requires a double dose, one from each parent although this has not actually been demonstrated.  Finally, melanistic squirrels produce eumelanin in excess to that of the wild type, possibly under the influence of Melanocyte Stimulating Hormone from the pituitary.  There is no a priori reason to think that this condition has to be recessive as suggested by Shorten (1945).  There is no missing “ingredient,” only a change in proportions.  The fact that crosses between melanistic and wild type squirrels produces intermediate offspring as reported in Searle (1968) means that this trait is not recessive according to the classical definition.

One additional variant should probably be mentioned here.  Its not uncommon to observe a tan, ochre, or “blond” Eastern Gray Squirrel.  This condition is thought to occur when eumelanin (black/brown in color) is “diluted” by a proponderance of phaeomelanin (yellow/red in color).  There is some question as to whether the difference in color is due to an actual difference in the pigment polymers themselves or the protein matrix in which they are embedded (in the so-called melansome, an enlarged vesicle produced by Golgi bodies filled first with the protein matrix into which the polymerized pigment is later added).   The usual stated chemical difference distinguishing the two pigment complexes is the presence of sulfur in phaeomelanin when the amino acid cysteine is readily available.  Cysteine is the only sulfur bearing amino acid (amino acids being the building blocks of proteins).  Sulfur bearing amino acids are capable of forming S-S cross bridges.  Such availability of cysteine thus might be expected to change the nature of the protein matrix in which the pigments are embedded due to these cross bridges.   According to Searle (1968), the protein matrix associated with the phaeomelanin complex is more condensed and less well organized than that which we refer to as eumelanin.  The resulting change in the physical shape might account for the color shift.  Any number of gene subsitutions (mutations) might account for this and it is surprising that this variant is not observed more often.   Interestingly, the one shown here has a white tail.  It is not uncommon to observe two tone squirrels but like the one shown here, it is usually the tail that is unpigmented rather than the body.  Perhaps, that has to do with the smaller target (diameter of the tail) for migrating melanoblasts to find.

Mating between coat color variants is probably random or non-assortative.  Coat color is not nearly as much a factor as hormonal attraction. Squirrels have two breeding seasons per year, one in winter and one in summer; within those periods, each mature female will enter estrus on a different day but only for that one day. When a female enters estrus, interested males come from hundreds of yards away and camp out at her “door step” (outside her nest) before dawn without every seeing her coat color. Most accounts of “courtship”, itself, are brutal with little opportunity for females to be selective by any means, let alone coat color (Steele and  Koprowski, 2001).  Fortunately for her, she is only “receptive” and pursued by males for that one day during each breeding period. During that time, she may be impregnated by several different males, none of which help raise the young.  That is one reason piecing together the genetics of coat color variation in squirrels is so difficult.

Occasionally, the frequency of white variants in an area increases sufficiently and remains stable long enough to establish what is referred to as a “colony.” Dr. John Stencel restricts the use of the term ”colony” to those locations in which at least 20 individuals (in absolute numbers) are regularly observed to be white in what is otherwise a normal gray population. I use a more “liberal” definition of a colony including all those communities in which white variants are repeatedly or regularly observed without any attempt to set absolute threshold numbers.   Those populations are probably harboring a permanent reservoir of the white-predisposing gene(s). But whatever the definition, there are to my knowledge, no colonies of the Eastern Gray Squirrel approaching 100% white. There are approximately nine known colonies of true albino squirrels (see map of colonies in “Overview of Findings” post; these are self-reporting observations) including the best studied one in Olney IL where a few hundred white squirrels make up approximately 12% of the population.  There are a similar number of leucistic colonies but their percentages never reach double figures.   I believe that Brevard’s population, with almost one in three white, has the highest percent white of any known colony and with approximately a thousand individuals within the original city limits (3 square miles), it is far and away the largest of such “colonies.”

Although it has been very successful in our area, it is rare elsewhere including its native Florida.  Despite being widely distributed throughout central and northern Florida, this variant occurs in such low frequency that most Floridians are unaware of its existence (See discussion of Melanie in “Overview of Findings” post).   However, they thrive in a few areas like Sopchoppy and the pecan orchard in Madison where our squirrels allegedly came from (for more on the Florida connection, see the “FAQ” post).  Once introduced in Brevard, they have thrived here, as well, and in other areas into which they were released (e.g., Walkerstown NC).  Perhaps the “Adam and Eve” translocated from Florida to North Carolina were unusually vigorous for reasons genetically correlated but not directly related to coat color.   Or perhaps the visibility which we assume makes them vulnerable to predation actually protects them from a greater threat, the automobile.  It’s also possible that predators, such as hawks, have “search images” that don’t match with white prey**.  But why would that benefit populations in one area but not another. 

Email your questions or white squirrel sightings to me at rrglesener@gmail.com

* Steppan, S.J., B.L. Storz, and R.S. Hoffman. 2004.  Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1.  Molecular Phylogenetics and Evolution 30 (3):703-719 as reported on page 13 of Thorington and Ferrell (cited below).

** In this context, the following anecdote my have some relevance.  A Brevard resident had visitors who brought their dog.  Squirrels were very abundent in her neighbor and there are about equal numbers of white and gray.  The dog regularly gave chase to gray squirrels but just stared at white ones.

Some Squirrel References I have found useful

Burgin, Jennifer.  Notable Observations. http://brevardnc.org/whitesquirrelinstitute/Burgin_Jennifer.htm

Dalzell, Bonnie. 1997. Canine Coat Color – Inheritance and Appearance (coat colors and coat color inheritance in dogs) with an emphasis on Colors in Borzoi. http://www.borzois.com/coat.color/coat.color.html

Long, Kim. 1995. Squirrels: a Wildlife Handbook. Johnson Books, Boulder. 181 pp.

Searle, Antony G. 1968. Comparative Genetics of Coat Colour in Mammals. Logos Press, London. 308 pp.

Shorten, M.  1945.  Inheritance of melanism in grey squirrels.  Nature: 156: 46

Steele, Michael A., J.F. Merritt, and D.A. Zegers (eds). 1998. Ecology and Evolutionary Biology of Tree Squirrels. Special Publication #6 of the Virginia Museum of Natural History, Martinsville. 311 pp. (Proceedings of the International Colloquium on the Ecology of Tree Squirrels, Powdermill Biological Station, Carnegie Museum of Natural History, 22-28 April 1994)

Steele, Michael A. and John L. Koprowski.  2001. North American Tree Squirrels. Smithsonian Institution Press, Washington. 151 pp.

Thorington, Richard W. Jr, and Katie Ferrell. 2006. Squirrels: the Animal Answer Guide. The Johns Hopkins University Press, Baltimore. 183 pp.

Wolpert, Lewis, Rosa Beddington, Jeremy Brockes, Thomas Jessell, Peter Lawrence, and Elliot Meyerowitz.  1998.  Principles of Development.  Oxford Universy Press, Oxford.  484pp.

25 Responses to “What is a White Squirrel?”

  1. Jean Harris says:

    We are from Cherryville, NC, and spotted an individual white squirrel that does not have the markings of your Brevard squirrel. It, however, is not a albino because it has dark eyes. It is all white with no markings and pinkish/white ears with black eyes. The grey squirrels, here, would try to intimidate it and chase it away. The white squirrel would show up daily at 9 in the morning and 5 at night to eat. We do have a picture (as does our neighbor) but we could not attach it to this comment. We would like to know if this squirrel is related to your Brevard squirrel or a breed of its own.

  2. It’s wonderful to find sites along with material and thanks a lot for the discuss that you’ve gave. Generally, I’m quite pleased, but etc…

  3. Dan Roseberry says:

    Hi
    I live in Petersburg, Illinois and spend a lot of time in the outdoors. I saw a red squirrel today at Lincoln’s New Salem State Park with a white “sweater” on. It looked much like another one that I spotted about a mile away from there about three or four months earlier. I was not able to get a picture of the one I saw today but I did get three snapshots of the one I saw earlier. If you would like for me to forward them to you I would be glad to do so if you would send me an email address. I would have sent them with this note but I do not see any provision for attachments. Just let me know. Dan Roseberry

  4. [...] a few rough drafts, we came up with the idea of using the Brevard White Squirrel (indicative to the area) as the “hiker.” I sketched up a few squirrel images and we [...]

  5. Amber says:

    I have seen a whitish squirel in Mount Holly NC…I have seen this one a few times driving to work, I about wrecked the 1st time b/c I have never heard of them before n didnt know what to think :) lol

  6. Metalsky Family says:

    We have seen a white squirrel on 3 separate dates in the past couple of months in Henderson county. Uncertain if the same one each time, or sitings consist of several. Most recently, now we saw white squirrels for several consecutive days nearer Brevard county, in the forest areas that were lakeside. They were distinctly not albino, no mistake. Each incident has been in the early mornings. Notably, the white squirrels avoided going near the dry corn that was “placed out” for wildlife feed – and which was devoured openly by the traditional grey squirrels. The white squirrels burrowed in the bushes, and we noted they had unusually bushy tails or “flufflier” tails than what we consider as the usual standard. Another white squirrel had a very thin tail by contrast – and yet it was without any doubt holding the record for the very longest tail we have ever seen on any squirrel in all our years! Got a few pix that are undeniable to include both the bushy tail view and show the amazing length of the other’s tail…… yet they are not the best quality shots since these elusive animals just refused to stop moving ;)

  7. [...] recently took a weekend trip to Brevard, NC, and upon arriving into town a WHITE squirrel ran across the road. This was particularly exciting [...]

  8. Megan says:

    Just saw a white squirrel with black marking on head and down back at Angel Oak Johns Island SC.

  9. Alec Scott says:

    We live in Orange, Texas. We had two white squirrels for a long time in our area. About a year ago one of them was killed by a car in the road, however, the other still comes into our yard on a daily basis. It is very territorial and does not like other squirrles coming around. It seems to have a nest near our home

  10. Donna Zell says:

    I live in Novato California and saw a blonde squirrel in my back yard two days ago. I have lived here for 15 years (in this house) and we have never seen a squirrel this color. We have lots of grey squirrels however on our oak covered acre. I say blonde because it was not white but rather a pale yellow color. Very cool.

  11. Donna Zell says:

    I have pictures of it.

  12. joanne says:

    we have a white squirrel,,and we see it all the time,its bigger then the grey ones,,and we have it on video tape

  13. Suzette says:

    there have been at least a couple of years of white squirrels being spotting in Brooklyn Park, MN.
    mainly in the area about the Stonybrook Condo complex.

  14. Tom says:

    I live in Northeastern Ohio. I have two male squirrels in my yard since late spring. They are reddish (?) in color, but their tails are pure white. The core of the tail is black, with long white hair coming from it. The appear somewhat tame…the one will follow me up the rail of a ramp on my house, and wait for me at the window to bring him some peanuts. I have seen them wrestling and playing in the grass, and the seem to get along with regular red tail squirrels. Any ideas of what they are, or have they been seen in this area before?

  15. Elan says:

    I just saw a white squirrel in Houston, TX.

  16. Karen Ensworth says:

    Carrabelle, Florida is my home now, having just moved from PA. This morning I awoke to see a white squirrel with a black strip down its back, in my front yard. It has black eyes. There isn’t a black marking on its head. I’m in northern Florida, is this a common squirrel for this area?

  17. Paula Schilling says:

    I live in Indianapolis, In. in a wooded area within the suburbs.Frequently a grey squirrel with white haunches has shown up to feed. Over several weeks, we have seen the same white squirrel increase the area of white until its whole head and body are solid white while the tail has remained grey.

  18. shawn Dilley says:

    There is a very large breeding population of entirely white squirrels with pink eyes in St Louis Park Minnesota. They have been here for many years. Three years ago our resident white mom had two gray babies and two white babies. We know this because we watched mom move her kids to a new home.

  19. Lisa Gordon says:

    I live in Citrus Heights California. I have noticed in recent years a large population of black squirrels in this rural area of the city. Just yesterday while driving out I saw a friend talking picturs of something in a tree, it was bright all white squirrel. I am waiting for her to post the photos but I believe it had dark eyes.

  20. A friend and I spotted a completely white squirrel in Huntsville AL on a hike through Monte Sano State Park. We couldn’t get close enough to see the squirrels’ eyes. We tried to get a photo, but it was too shy to capture an image. Totally cool to have seen it though!

  21. GKTW Volunteer says:

    I volunteer at a resort in the Orlando/Kissimmee FL area, Give Kids the World Village, that hosts children with life threatening illnesses (Wish kids). We have at least two on the property. They have dark eyes and are all white.

  22. Gail Evers says:

    I will in Douglas, Massachusetts….have a white squirrel feeding on my bird feeder in my yard….have been able to snap a few pics..very cool have never seen a white squirrel before!!!

  23. robert mamer says:

    I have seen a white squirrel off of oak and fairoaks. during the month of april/2013 very nice.

  24. Ipek Ozay says:

    I am from Raleigh,NC. Today I saw a creme color one,tail was a little darker, he just like “Flame point” called cats. I got very excited, I am 57 and the first time in my life I saw an extraordinaire squirrel,I stopped my car right away to take a picture,but wit a cell camera it was impossible. I wish I had a good camera so I could be able to capture a pic of him.

  25. MARIA MILLER says:

    I seen a white squirrel with a brown tail, today playing with the many brown squirrels, in our yard. What a treat. I have never seen a white squirrel before, pictures of them is all. June 6th, 2013

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