The Hunt for the Great White Squirrel

Gray squirrels are, well, gray.  But not completely gray.  Many have brown mixed in with the gray and most have a white belly.  In our corner of North Carolina, we have the eastern gray squirrel (Sciurus carolinensis).  Its scientific name means squirrel of the Carolinas, but the eastern gray squirrel ranges from south Florida to southern Canada and west to where the forests give way to the prairies. 

Gray squirrel with normal coloration.

Recently a friend told me of a white squirrel in her suburban neighborhood.  Diane and I decided we would have to hunt for the great white squirrel.  Unlike Ahab who had to search three oceans to find his prize, we drove through a leafy suburb.  There were lots of squirrels, on the lawns and in the trees but they were all gray.  Then, rounding a corner, we saw it.  The white squirrel bounded across the road, into a yard and ran up a tree.  We quickly noticed the squirrel was not pure white but had a gray patch on its head and a gray stripe down its back.  As we looked more closely, we could see this squirrel’s eyes and nose were dark.  This squirrel was a white eastern gray squirrel but it was not an albino.  Albinos cannot make the pigment melanin so they have white fur, pink eyes and pink noses.  This squirrel was leucistic, able to make melanin in parts of its coat, eyes and nose but could not make melanin in the rest of the its body.   A number of genes are responsible for leucism and our white squirrel undoubtedly had a mutation in one of these genes. 

Leucistic gray squirrel with gray
stripe down the back.

Leucistic gray squirrel showing
 white fur, gray on top of
head  and dark eyes.

White squirrels are rare because the mutations happen infrequently and because the white squirrels that are born are easy for predators to see and catch.  We have been watching this white squirrel for a month and it has not been caught by a hawk or coyote.  If this squirrel reproduces, there is a chance some of its offspring will be leucistic too.  The white squirrel may be able to survive in this neighborhood with the help of people.  They could provide food in bird feeders and limit threats from predators.  

The mountain town of Brevard, NC has a famous population of white squirrels established in the 1950s.  Brevard passed an ordinance to protect the squirrels and has an annual White Squirrel Festival complete with fun run, bands, food trucks and a white squirrel photo contest.

White forms of animals have cultural and spiritual significance around the world.  The white buffalo is revered by the native people of the American plains.  According to the Kitasoo Nation, Raven made the Spirit Bear, a white variant of the American black bear found on the coastal islands of British Columbia, to remind the people of the age of ice that came before.  The Tsonga of South Africa consider the white lion as most sacred.  For Captain Ahab, Moby Dick was a manifestation of evil.  Beyond genetics and natural selection, I wonder about the meaning of this white squirrel. 

Nitrogen is Expensive, Carbon is Cheap

Bradford pear (Pyrus calleryana) showing red color
from anthocyanin,and yellow from xanthophyll.

Every fall, trees put on a spectacular show.  As the days get shorter and the nights cooler, trees undergo a transformation.  From the maple forests of New England to the aspen groves of the American west  trees show a fantastic range of colors; red, orange, yellow, purple.

This extravagance is the basis of an important tourist industry, catering to “leaf peepers”.  Vermont’s hotels and restaurants bring in more than $100 million dollars in October much of that from people coming to see the colors. 

From spring to later summer, most trees are green.  The shade of green in trees shows a wide variation between species but all those shades are due to the photosynthetic pigment chlorophyll.  This biochemical workhorse, found in the chloroplasts of leaves, participates in food production and oxygen generation from spring to fall.  Chlorophyll is not the only photosynthetic pigment in leaves.  Carotene and xanthophyll are present in the chloroplasts too and work in concert with chlorophyll to carry out photosynthesis.  Carotene is orange (it gives carrots their color) and xanthophyll is yellow.  Plants have another type of pigment called anthocyanin that comes in many colors including red and purple.  Anthocyanin is not involved in photosynthesis but protects plants from environmental stress.  In summer carotene, xanthophyll and anthocyanin are invisible because there is so much chlorophyll in the leaves. 

Leaves of sugar maple (Acer saccharum) with a
range of fall colors 

The reason we have fall color is chlorophyll contains nitrogen.  Nitrogen is usually in short supply for plants.  They have to take up this scarce resource from the soil, sometimes with the aid of symbiotic fungi associated with plant roots.  Plants then transport the nitrogen up to the leaves where it is used to make chlorophyll. 

Deep red anthocyanin in the leaves of
Euonymus americana

                                                                                      Carotene, xanthophyll and anthocyanin are made only of carbon, hydrogen and oxygen.  These elements are available in abundance for the plants coming from CO₂ in the air and H₂O taken up by the roots.  For plants, nitrogen is expensive and carbon is cheap.  In the fall, trees do not want to waste the expensive nitrogen in chlorophyll by dropping it with the leaves, so the chlorophyll is broken down and the nitrogen stored in twigs for use in next year’s chloroplasts.  As chlorophyll disappears from leaves carotene, xanthophyll and anthocyanin can shine through.  These pigments are not recycled because they are made of cheap resources and the trees drop them to the ground with the leaves. 

As we move from the bright green of summer to the brown of winter let’s thank cheap carbon and expensive nitrogen for the dazzling fall show.

The Disappearance

When birds are migrating in spring it is fairly easy to notice when a new species arrives.  One day yellow-billed cuckoos are not here and the next day they are.  But in fall migration it is harder to track the disappearance of a species when they fly south.  Since absence of evidence is not evidence of absence, we paid particular attention to the last date we recorded Chimney Swifts and Ruby-throated Hummingbirds in our area.  These small birds undertake heroic migrations in the fall of the year.  Some Ruby-throated Hummingbirds fly non-stop across the Gulf of Mexico and Caribbean Sea to their wintering territories in Mexico and Central America.  Others take the land route around the Gulf through Texas and further south.  Chimney Swifts winter in the Amazon Basin of South America with a hazardous migration similar to that of the hummingbirds. 

We had a hummingbird family in our yard this summer.  A male and a female visited our feeders daily and later in the summer at least one immature hummingbird was with them.  Then in August, the male disappeared.  Did he and the family go south?  Absence of evidence.  In August and into September large numbers of female and immature hummers were in our yard drinking the sugar water.  The number of hummingbirds started to decline in October and we made the final sighting of the year on October 19. 

Chimney Swifts entering a chimney at sunset

Chimney swifts disappeared a few days before the hummingbirds, on October 15.  In the fall of the year, you can find large flocks of migrating chimney swifts around their roosting spots.  Since these birds cannot perch on a limbs or wires, they must cling to a vertical surface, like a chimney, to nest or sleep. Before Europeans entered the new world, Chimney Swifts probably roosted in hollow trees and on cliffs.  

 A local high school has a stack for an unused furnace that is ideal for a chimney swift roost.  We have recorded over 3000 swifts flying into this stack during September.  The swifts begin flying near the chimney around sunset giving their chattering call.  Then the number grows and they begin to form a vortex of swifts hundreds of yard wide.  A half an hour after sunset as the light is disappearing the swifts begin to enter the stack.  The vortex gets smaller and smaller until the last swifts fly into the chimney as total darkness descends.   

We look forward to these birds showing up again next spring.