Distribution of White Squirrel Colonies
Description: Brevard is not the only community to host a white squirrel colony.  There are approximately a dozen other cities with similar populations. The most famous of these is in Olney IL where Dr. John Stencel has been studying an albino population for more than 30 years. These albinos suffer from a mutation in the ability to make the dark pigment melanin. Not only do they have no coat markings but they have pink or blue eyes. Melanin in the eyes helps reduce glare and improves visual acuity. Thus, albinos have impaired vision, a distinct disadvantage for an animal doing “high wire” acrobatics in the treetops. It’s not surprising that the Olney white squirrel has shown signs of decline. The Brevard white squirrel does not suffer from this disadvantage. Besides patches of pigmented hair, they have dark eyes (see Typical Brevard White Squirrel photo below). The only other known colonies with this pattern are either derived from the Brevard population or found in the southeast, especially Florida to which there seems to be a direct connection (more on the Florida connection later).  In preparing this map, I am using a rather “liberal” definition of a colony. Dr. Stencel restricts the use of “colony” to those locations in which at least 20 squirrels (in absolute numbers) are regularly observed to be white variants. Here I list all those communities in which white variants are repeatedly or regularly observed (self-reporting) without any attempt to set absolute threshold numbers since those populations are probably harboring a permanent reservoir of the white-predisposing gene(s). But whatever the definition, there are to my knowledge, no all white colonies of the Eastern Gray Squirrel in North America. I believe that Brevard’s population has both the highest percent white (approximately 1 of every 3 squirrels) and abundance (~ 1,000 white squirrels) of any known colony.

Isolated sightings of white squirrels (usually with dark eyes but no coat markings, a condition known as leucism) occur regularly through out the entire range of the Eastern Gray squirrel. This common mutation seems to be weeded out before it can be firmly established into a so-called colony. For a partial list of such isolated sightings, click here.  (You can also email your sightings to rrglesener@gmail.com).

Typical Brevard White Squirrel
Description: The Brevard white squirrel is not albino. In addition to a mostly white coat, it has dark eyes, a pigmented head patch, and a dorsal stripe that usually expands to form what looks like a saddle in the shoulder area. There is much variation in this pattern but an all white squirrel is extremely rare in this area. 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 (like Count Dracula). There is some evidence that this pattern is inherited (Burgin: Inheritance of Head Patch Patterns).  For more detail, see the post entitled “What is a White Squirrel?”

Typical Gray Squirrel
Description: Even without the white variant, there is much variation in tree squirrel coat color both locally and regionally. Most are counter-shaded, with a gray/brown top and near white bottom. The white belly is adaptive in that it makes the squirrel less visible when viewed from below against a light sky. Thus, normal gray squirrels have all white patches on the abdomen while the Brevard white squirrel has pigmented hairs on the forehead and back. The difference between the two is not the ability to make the dark pigment melanin (as is the case in albinos) but rather in the distribution of the different hair colors. It is as if the region normally restricted to the belly has expanded at the expense of the pigmented hairs, confining them to a narrow region along the back. The gene(s) involved is like the conductor of an orchestra; it doesn’t actually make the music we hear (in this case the pigment we see) but it directs the production of music from the orchestra (melanin production by the pigment producing cells). Such genes are called regulator genes. Another theory  (click here) for which there seems to be some evidence in other mammals suggests that this pattern might result from a shortage of melanocytes (the pigment producing cells) which must migrate throughout the body in early development. If the normally dark dorsal surface has a higher priority and/or greater attraction for these cells, the result would be a mostly white squirrel with pigmented patches on the backside, i.e., a Brevard white squirrel. In any case, nothing is known about its inheritance, but circumstantial evidence (rapid increase in frequency) hints that it may be a dominant trait, unlike the recessive condition of albinos.  For more details, see the post “What is a white squirrel?”

White and Gray Siblings
Description: These two squirrels are juveniles of the same age. They were foraging peacefully together. I am almost certain that they are siblings from the same nest. In North America, so-called white squirrels are simply coat color variants of some squirrel species, in this case, the Eastern Gray Squirrel (Sciurus carolinensis). Brevard’s white squirrels freely interbreed with the gray variant and have mixed litters that are either gray or white as in this picture but nothing in between. Geneticists call this condition a dimorphism, in this case a color dimorphism similar to variation in eye or hair color in human beings.

This photograph also illustrates the difference in perceptibility between the two variants. Clearly the white variant is easier to see. When squirrels foraging on the ground are frightened, they head to the nearest tree and do a “spread eagle” on the trunk. The gray squirrel blends in and is camouflaged but a white variant sticks out like a “sore squirrel.” They are behaving in a gray squirrel appropriate way. In fact, in every way other than coat color, white squirrels appear to be normal Eastern Gray Squirrels. No differences in behavior have been documented although I have received many causal observations of one or the other being more aggressive at back yard feeders. Gray squirrels who have not encountered the white variant (and vice versa) may behave somewhat “suspiciously” to their counterpart but those that have been raised together show no evidence of ostracizing the other (as the capturers of Melanie feared – see the Melanie section for more information).

If white squirrels are more visible to people, we can assume that they are also more visible to predators. Perhaps, that is one reason why, despite its wide distribution, the white variant is usually found in close association with humans where natural predators are reduced. Domestic pets are a threat though once in their element (trees), squirrels can usually escape with ease. Collisions with cars are probably a more serious threat to squirrels and being more visible may actually be an advantage in avoiding accidents, particularly in a community that values this distinctive animal. I have been told by a number of people “I brake for white squirrels but not gray ones.” They also let white squirrels forage at their bird feeders but shoo away gray ones. Maybe this is why the white variant has increased from a single pair in the 1950’s to close to a thousand in the city today. It may also be true that predators are not genetically programmed to search for white prey or that some, as yet undiscovered, factor correlated with coat color gives them an advantage.

Geographic Distribution of the Brevard White Squirrel
Description: In 1987, I wrote a letter to the Editor of the Transylvania Times requesting people to send me sightings of the Brevard white squirrel outside of the city of Brevard. Later, once the Fall count was established and advertised, I received sightings from people who read articles in a number of regional newspapers. This map shows the compilation of the sightings I received over a twenty-year plus period (for a larger version of this map, click here).  A single asterisk usually represents numerous sighting in that community. You can see that although the white variant began as a pair released on Johnson Street just south of Main in the early 1950’s, they now span an area almost 50 miles in diameter, from west of Cashiers in Jackson County to east of I-26 in Henderson County, from Saluda in Polk County in the south to north of Asheville and Enka/Candler in Buncombe County. However, the distribution is not continuous. While there are large numbers in Etowah and Laurel Park, there are relatively few in between in Horseshoe. This disjunct distribution suggests that much of their dispersal may be human assisted (capture and release; the same way that they arrived in Brevard in the first place). However, it may also be partially accounted for by habitat fragmentation. White squirrels are gray squirrels and gray squirrels are tree squirrels. Tree squirrels depend on trees for food, shelter, and refuge from predators. In areas where trees have been cleared, gray squirrels of either variety are rare (see section on Habitat Fragmentation).

Percent White Squirrels by Sector for 2011 Count
Description: This map shows the study area, which is approximately 3 square miles, centered on the Courthouse and basically follows the original city limits. Brevard Middle School is to the north, Brevard High School to the south, Brevard Elementary School to the east, and Brevard Music Center is just to the west of Sector 9. There are 35 Sectors of varying size averaging about 50 acres. The percentages shown for each Sector are for the most recent count in which about 4/5 of the study area was covered. As you can see, there is some degree of variation over the study area indicating that this is not one big homogeneous breeding population. This suggests that habitat fragmentation, possibly due to loss of trees, is already having some effect on dispersal. The highest percentages appear to be along the eastern margins. The combination of a relatively high percent of the white variant and the increased visibility within a park-like landscape make Brevard College (indicated on the map by BC) an ideal place for visitors to see their first white squirrel.

2011 Overall Results
Description: These are the overall results from the most recent count  The average percent white and total percent white are in agreement; both indicating that slightly more than 4 of 10 (40.3%) squirrels in Brevard are of the white variety. Prior to 2005 that ratio was closer to 1 of 4. Some of the increase may be due to changes in protocol. For instance, in order to encourage volunteer participation, we extended the observation period through December (instead of just October). Although leaf fall made observations easier, the colder temperatures and unavailability of nuts probably meant that there were fewer squirrels out foraging at any given time. We also allowed observers to select a time interval convenient for them. Since squirrels are bimodal in their daily foraging activity with peaks in the morning and afternoon, some observations were probably made during reduced squirrel activity. The effect of sample size on the reliability of estimates was noted in a previous section. Perhaps this accounts for some of the increase, although I think we can safely say that the white variant is doing well at this time.  In fact, I am convinced that the white variant is steadily increaseing and my be in the majority in about ten years (see section “Is the Percent of the White Variant Still on the Increase? below). For more detaiedl results for this year click here and for previous years click here.

Blank Sector Map and Data Sheet
Description: Besides a roadmap directing them to their assigned Sector, volunteer counters receive a detailed Sector map and data sheet on which to record their observations. Using the map, observers navigate their Sector at a leisurely pace usually taking between 1-2 hours. Upon sighting a squirrel, the volunteer places a “G” (for gray) or “W” for (white) on the map at the approximate location. Since squirrel nests indicate the presence of a resident squirrel, volunteers should slow down and observe more carefully when a nest is seen. Squirrel nests look like big sloppy bird nests and are usually located in forks between branches 15 feet or more above ground (tree cavities also serve as nests but usually can not be seen from the ground). Nests are recorded on the maps with an “N”. Other indications of a squirrel’s presence are hearing any number of various squirrel calls, seeing stripped tree bark, or simply hearing a rustling in the bushes or leaves. Of course, unless a squirrel is seen, we have no idea of its coat color. Squirrel movement can be quite quirky. Sometimes it is hard to tell if you are seeing more than one squirrel or the same one cutting back and forth. This type of error is hard to eliminate but there is no reason to assume it occurs more with one color variant or the other. The data sheet also has places to record behavioral activity, etc. but these are icing on the cake. The bottom line is simply how many white squirrels and how many gray squirrels were observed.

Completed Maps from Sector 19
Description: This is a comparison of the completed maps of all three counts for Sector 19 in 1999. Note how variable the results are for this particular example. This may be due to differences in the observers, weather, date, time of day, or any number of other possible factors. That is why we like to have a least 3 counts for each Sector. Also, count #3 indicates the importance of sample size. If one of the gray squirrels observed had not been seen, the percent white would have jumped to 67%. If one of the whites observed had not been seen, it would have dropped to 33%. The same changes would have had much less effect on the other two counts. Clearly, the more squirrels we observe, the more valid the data are. This is why we average our results. We do this in two ways: (1) by calculating the average of the 3 counts, and (2) by calculating the total white observed over all three counts divided by the total squirrels observed (note: easy to see squirrels may be observed in all three counts). To the extent that the two measures agree, we think they provide an accurate estimate of the true percent white.

Bar Graphs of Abundance and Percent White 1997-2010

Description: These two graphs illustrate the most significant result of fourteen years of study. Despite fluctuating widely in abundance (calculated as squirrels observed per individual count*), the estimated percent white has, if anything, shown a slight gradual increase. The percent white started off in the low to mid 20′s but last year’s (2011) result was 40.3%.  The fifteen-year average is 29.0%. The error bars on the graphs indicate the 95% confidence levels for the true percent. For any pair-wise comparison, if the error bars overlap, the difference is not significant. As you can see, whereas many of the year by year comparisons for abundance are significantly different, very few of the percent-white ones are.  Never-the-less, the next section will use a different type analysis to argue that the white variants are increasing in frequency and appear to have some advantage (possibly human preference).

*The Fall squirrel count is not meant to be a census. We know that in the one to two hour period of observation, not all squirrels in a Sector will be out foraging. We also know that many of those out, will not be seen for a variety of reasons. Thus, the squirrel count underestimates the total number of squirrels (there are other methods to estimate total abundance). It is meant primarily as a means to estimate percent white. However, year-to-year comparisons of abundance can be made if one compares squirrels observed per individual count and that is what is shown in the abundance graph.

Is the Percent of the White Variant Still on the Increase?
We have just completed the 15th annual Brevard Squirrel Count.  Ten years ago I analyzed the data and concluded that the percent of the white variant was remarkably stable, especially when compared to the wide fluctuations seen in abundance.  However, after ten more years I am tempted to revise that conclusion to suggest that not only did their numbers increase from near zero in 1951 when a pair was released to approximately a thousand today (in the study area alone) but that the percent white continues to increase today.  The above bar graph hints at that but the scatter plot below shows it more clearly.

Applying a least squares regression yields a trendline with positive slope.  The R-square value  tells you how much of the variation of the variable plotted on  the y-axis is accountable by that of the x-axis.  Theoretically, R-square ranges from 0 to +1 (the latter would be equivalent to 100%).  In this example, R-square = 0.861.  In other words, 86.1% of the variation in percent white is accountable by time.  That is highly significant.  If one were to extapolate backwords to estimate the orgin of the white variant, the trend line would give the year 1980.  While this is more recent than the actual date (1951), it is in the ballpark, especially when one considers the initial lag time often associated with growth curves.   Extrapolating into the future, we might expect the white variant to become the majority in the early 2020′s if the current trend continues.

This data can also be used to argue that the gene(s) pre-disposing a squirrel to be of the white variety is dominant over that for the gray.  The argument is circumstancial and somewhat technical but I think convincing.  If you’re prepared to tackle it, click here.  When you’ve finished, I’d appreciate any feedback you might like to offer.

Relationship between Squirrel Abundance and Hard Mast
While percent white has remained relatively stable or even showing a steady increase as indicated above, abundance has fluctuated widely.   One might expect abundance to be a function of food availability.  Squirrels are omnivores and will exploit seasonally available resources of all kinds.  But it is probably winter that presents the biggest challenge for these warm blooded rodents who do not hibernate.   For the most part, squirrels depend on two food sources to fuel their metabolisms during this bleak time of the year: (1) backyard bird feeders and (2) nuts cached away during fall only to be relocated during winter.  The latter are known as hard mast (to be distinquished from soft mast or fruits and berries which must be eaten on the spot).  The Forest Service has been estimating hard mast for western NC since 1983 (Olfenbuttel 2010).  Only one of their stations is in Transylvania County and it is some distance from the city of Brevard.  Never-the-less, I compared abundance of squirrels during the annual count to average total hard mast.  Both are measured in the fall.  The results are shown in the following two scatter plots.

The figure on the left shows the relationship between squirrel abundance and the amount of hard mast of that same year.  As you can see, the trend line is relatively flat (and actually shows a slight negative correlation), with hard mast accounting for less than 5% (R-square = .0498)  of variation in squirrel numbers.  However, if you compare squirrel abundance to hard mast estimates of the previous year, there is a strong positive correlation, with hard mast accounting for over 50%  of variation in the Brevard squirrel population (R-square = .524).  In fact, if soft mass (fruits and berries) of the previous two years are also included, R-Square is slightly greater than 0.6 (.603).  This makes sense since squirrel nutrition and therefore the amount of energy allocated to reproduction should be a function of how well they have been nourished in the recent past, not how much food is currently available for harvest.  During bleak years female squirrels may “skip” one or both of the two breeding seasons or have smaller litters in order to increase their own chances of survival.  But they are capable of quickly compensating following banner years.  To my knowledge, this is the first reported such relationship between squirrels and mast and can be added to similar observations in deer mice and chipmonks (Wolfe 1996), and woodrats (Mengak and Castleberry 2008).

Melanie

Description: This is a photograph of Melanie (named for her reduced levels of the dark pigment melanin) taken by David Gale formerly of the Back to Nature Animal Rehabilitation Center in Orlando FL. Notice that she is not only white but has the same pigmented markings as the Brevard white squirrels, i.e., dark eyes, head patch, and a dorsal stripe that broadens into a saddle in the shoulder region. Melanie was captured near Disney World and brought to Back to Nature, not because she was injured, but because her capturers feared she would be “picked on” by normal gray squirrels. This concern indicates to me that the white color variant was uncommon in the area. However, when David placed an article in his monthly newsletter about the white squirrels of Brevard NC, I received numerous emails noting similar sightings from the counties surrounding Orlando. They are apparently well established in that area but in low frequency. Since then I have received sightings from Jacksonville, Tallahassee, Sopchoppy, Panacea, Pensacola and regions in between. This is consistent with local Brevard folklore that says our white squirrels are transplants from north Florida. But it also suggests that the color variant may be widespread and native to central and northern Florida (and possibly the low country of South Carolina and Georgia as I have had recent sightings from the greater Charleston area) rather than an escapee from a circus, also part of the folklore. For a detailed presentation of what we do know about the Florida connection, read Barbara Mull Lang’s account (click here).

If, in fact, Brevard’s white squirrels are native to Florida where they occur at low frequency, the question arises as to why they have been so much more successful in their adopted habitat. The woodlands of western North Carolina would seem to favor tree squirrels of all varieties. Perhaps the “Adam and Eve” transplanted from Florida were particularly vigorous for reasons genetically correlated but not directly related to coat color. Apparently, white variants were thriving within the pecan orchard population from which they were taken. The success of Brevard white squirrels transplanted to other areas (Walkertown NC and Yonges Island SC) supports this notion but the determinants of that success remain a mystery. As noted in the White and Gray Sibling section, other than coat color, Brevard white squirrels appear to be normal Eastern Gray Squirrels.

Whatever became of Melanie? David placed her into an open-air, captive colony of white squirrels being maintained at the Tallahassee Museum of History and Science that was established from captured white squirrels from the Sopchoppy area. For more on this topic, click here.

Habitat Fragmentation
Most of us think of our white squirrels as a curiosity. Certainly they bring us recognition and are the source of civic pride. For some, they bring more tangible benefits. As a tourist attraction they are a direct (souvenirs) and/or indirect (food and lodging) source of revenue. Wouldn’t it be a shame if while we were celebrating our unique critters, they were diminishing in number before our very eyes. That alone is reason to monitor their well being.

But there is a more fundamental reason for monitoring not just the white squirrels but squirrels in general. Squirrels live very intimately and harmoniously with humans. One reason for that is that we both share a preference for woodland/woodlot habitats. Not dense forest, but not open prairie, either. Anthropologists have demonstrated that humans prefer a shaded, park-like environment; one with scattered trees through which they can see distant objects approaching. We can speculate on why this should be so but the point being made here is that this preference is exactly the type of environment tree squirrels occupy. Their whole lives center on mature trees for food, shelter, and refuge from predators. When foraging on the ground, they are wary, always alert for possible threats. The further they can see, the further they will forage from their arboreal retreats but never more than a couple hundred yards. They are more abundant in such woodland habitat than dense forest.

Thus, a healthy squirrel population indicates a healthy park-like habitat, the kind of environment that attracted most of us to Brevard and Transylvania County in the first place. Squirrels are indicator species for forested ecosystems in the same way that certain fish and aquatic insects are indicators of good water quality. Economic and social pressures gradually impinge on this environment in ways that are often difficult to detect in the short term. However, decline in our squirrel population could be viewed as an early warning of habitat degradation giving us time to implement remedial action. As can be seen by comparing the city and surrounding forest in this aerial photograph, there has definitely been habitat fragmentation. The forest has given way to woodland/woodlot, our preferred habitat. But do we wish to “progress” further toward a treeless urban landscape. Squirrels can tell us how far we have traveled in that direction.

Over the last twelve years most of the fluctuation in squirrel abundance can be accounted for by variation in food (hard mast). That is a positive observation. On the other hand, the fact that the percent of the white variant differs widely over different parts of the study area, indicates that there are barriers to mobility. Instead of one large interbreeding population, we have a series of semi-isolated sub-populations. Conservation biologists claim that such subdivisions are unhealthy for species preservation. Are we on the verge of impacting our preferred habitat? Monitoring our resident squirrels, both white and gray, is more than just a curiosity and should be promoted.

If you would like to participate in this or related projects please contact the Heart of Brevard (884-3278 and heartexec@comporium.net) or Bob Glesener, Director, White Squirrel Research Institute (862-3231 and rrglesener@gmail.com) for more information.

GLESENER, ROBERT. Associate Professor of Biology, Emeritus, Brevard College. B.S., University of Maryland (Zoology); M.S. (Zoology) and Ph.D. (Biological Sciences), University of Michigan.

 I first heard of Brevard while an undergraduate at the University of Maryland. Southern Appalachia is salamander heaven and I spent my summers in Western North Carolina trail blazing and collecting specimens for a zoology professor. I was hooked. I gave up my prior interest in medicine and psychology and became an ecologist. Even though my research eventually became more theoretical, to this day I cannot resist turning logs and rocks in Pisgah National Forest. The difference is that today I put back everything I catch.

I came to Brevard directly from graduate school at the University of Michigan. My research then dealt with (1) the regional stability of locally unstable predator/prey interactions and (2) the evolution and maintenance of sexual reproduction. During my twenty-six years at Brevard College, I have taught everything from Introductory Biology and Zoology to Ecology and Genetics. Outside the classroom I founded the Commuter Student Association and BC RECYCLES! I also maintained small projects monitoring stream water quality and the salamanders of Moore Cove, Pisgah National Forest.

In 1997, I began a long-term study of Brevard’s white squirrel population, which includes conducting the annual Fall Squirrel Count. Although I have since retired, I continue as Director of the White Squirrel Research Institute under the sponsorship of the Heart of Brevard.   You can contact me at rrglesener@gmail.com   Thanks for your interest (if you could possibly be interested in more about me, click here).

References:

Greenberg, C.H., and G.S. Warburton. 2007. A fast and reliable hard mast index from acorn presence-absence tallies.  Journal of Wildlife Management 71:1654-1661.

Mengak, Michael T. and Steven B. Castleberry.  2008.  Influence of acorn mast on Allegany woodrat population trends in Virginia.  Northeastern Naturalist 15(4): 475-484.

Olfenbuttel, Colleen.  2010.  Western North Carolina hard and soft mast survey report Fall 2010.  North Carolina Wildlife Resources Commission.  11 pages.

Wilson, E.O.  1984.  Biophilia.  Harvard University Press, Cambridge.  pp. 157.

Wolff, J. O. 1996. Population fluctuations of mast-eating rodents are correlated with production of acorns.  Journal of Mammalogy 77:850–856.