Posts Tagged ‘fox squirrels’

Genetic Study Suggests Fox Squirrels (Sciurus niger) and Gray Squirrels (S. carolinensis) May Interbreed

September 14, 2019

Naturalists have observed male fox squirrels chasing female gray squirrels.  Male Squirrels chase female squirrels during mating season, and if they catch the opposite sex, it demonstrates their fitness for procreation.  Fox squirrels have never been observed actually mating with gray squirrels, and as far as I can determine, nobody has ever reported an hybrid between the 2 species.  However, a new study suggests they may interbreed or have interbred in the past.

Fox squirrel a coat of many colors

Black fox squirrel.

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Melanistic fox squirrel I photographed outside Spring Island, South Carolina.  This was before I had the benefit of a telephoto lens.  Click to enlarge.

It is estimated there could be as many as 25,000 black squirrels in the east of England

Melanistic gray squirrel.

The mutation for having a black coat (melanism) arose twice in fox squirrels from 2 different populations–an example of convergent evolution.  Western fox squirrels have 1 allele associated with melanism, while eastern fox squirrels have a different allele associated with melanism.  (An allele is defined as 1 of 2 or more alternative forms of a gene that arose by mutation and are found on the same place in the chromosome.)  Scientists believe the alleles for melanism in fox squirrels arose for different reasons.  The black coat on western fox squirrels helped them stay warm and more active in a region with colder climate.  The black coat on southern fox squirrels helps camouflage them because it makes them harder for hawks to see in a shady canopy.  The allele for melanism in western fox squirrels is exactly the same as found in melanistic gray squirrels.  Statistical models suggest the most likely explanation is interbreeding between fox and gray squirrels, though they can’t rule out 2 other explanations.

The allele for melanism may have originated in the common evolutionary ancestor of both species.  Alternatively, the allele for melanism may have arisen first in gray squirrels and was passed on to fox squirrels.  But the most likely explanation is it arose in fox squirrels and was passed on to gray squirrels during interbreeding.

Melanistic gray squirrels are more common in the northern region of their range because the darker coat keeps them warmer when they are outside during winter.  The authors of this study believe the black coat helped gray squirrels colonize newly deglaciated territory following the end of the last Ice Age when the climate was still quite cold.  They didn’t estimate how long ago fox squirrels passed on the melanistic mutation to gray squirrels.  It seems likely this may have occurred a long time ago when both species had recently split from their common ancestor.

Gray squirrels were introduced to England and have now almost completely displaced native Eurasian red squirrels ( Sciurus vulgaris).  Melanistic gray squirrels are replacing the original population of gray squirrels that outcompeted red squirrels in England.

It’s easy to tell the difference between gray and fox squirrels.  The latter are generally twice the size of the former.  A juvenile fox squirrel may be about the same size as an adult gray squirrel, but it is still easy to identify the correct species.  Gray squirrels generally have a white belly, while fox squirrels are solid-colored on the torso and belly.  Fox squirrels often have masks; gray squirrels almost never do.

Reference:

McRobie, H.; N. Moncrief, and N. Mundy

“Multiple Origins of Melanism in Two Species of North American Tree Squirrels (Sciurus)”

BMC Evolutionary Biology   2019

 

 

Carvers Creek State Park in South Central North Carolina

October 27, 2015

Last Saturday, we visited my nephew who is stationed at Fort Bragg in North Carolina.  This gave me the opportunity to hike around Carvers Creek State Park located nearby.  Past the entrance, a long wide path borders an old field on one side and a woodland of shortleaf pine with an understory of blackjack oak and sweetgum saplings on the other side.  I heard a constant chirping of crickets in the field, and grasshoppers were also abundant.  This is ideal habitat for loggerhead shrikes (Lanius ludovicianus), a species in decline.  They nest in short trees but hunt for large insects (such as grasshoppers), mice, lizards, amphibians, and even juvenile venomous snakes; all of which can be found in this old field.  I’ve never seen a loggerhead shrike, and it’s high on my birding wish list.  I asked a park ranger where the shrikes were.  She told me they could usually be seen behind a fence where they keep their maintenance equipment, and birders using binoculars could stand near the fence and see them.  I didn’t have binoculars with me, so shrikes are still on my wish list.

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The first part of the trail borders an old field humming with crickets and grasshoppers.  Loggerhead shrikes inhabit this park.

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Much of the park is open woodland/savannah type environments.

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Big loblolly pine.

This path leads to the former winter house of one of the Rockefellers, but it is not yet open to the public.  The state park service probably needs to renovate it, so it’s safe for visitors.  Rotten floor boards can be hazardous.  It overlooks a millpond and has glassed-in porches on the 2nd floor of both the front and the back.

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The front of the WWI era Rockefeller winter home.

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Back of the Rockefeller winter home.  Most of the wildlife I did see was here behind the fence.  Note the glassed-in porch.  Nice.  It overlooks the millpond.

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Cypress trees ring the millpond.

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Millpond.

A live oak tree grows near the Rockefeller house.  Live oak is not native to North Carolina this far inland, though it does grow near the coast.  This specimen must have been transplanted here over a century ago.  I saw gray squirrels, chipping sparrows, and blue jays foraging on acorns under the tree.  One of the squirrels was rather large, and at first I thought it might be a fox squirrel, but I caught a glimpse of white underbelly.  Gray squirrels usually have white bellies, while fox squirrels are solid-colored.  The ranger told me fox squirrels can be seen on the loop trail around the millpond, but I didn’t see them.

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Live oak.

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The loop trail goes through a savannah.

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More open woodland/savannah.

I was surprised to see cypress trees growing this far inland.  Cypress trees grow on the edges of the millpond here.  I checked the range map and learned this site is about as far inland as they can normally be found.

The loop trail threads through open pine savannah.  I noticed fire marks on some of the pines.  This park must be managed with fire.

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The millpond is u-shaped. Note the cypress trees in the water.

Carvers Creek Park is a recent and valuable addition to North Carolina’s state park system.  Much of the area around the park has been transmogrified into pine tree farms, an environment that supports almost no wildlife at all.

 

Squirrel Migrations

August 24, 2012

When virgin forests covered much of eastern North America, vast armies of gray squirrels (Scirius carolinensis) periodically migrated over the landscape.  They swam across major rivers and swarmed over farmer’s cornfields, eating every last ear of corn.  The very first tax enacted in Ohio is a tribute to their former pestilence–all homesteaders were required to bring 3 squirrel scalps to the tax collector.  The following passage from the book, America as seen by its First Explorers, by John Bakeless illustrates this stunning phenomenom.

In the autumn hundreds of squirrels were sometimes found swimming from one shore to another.  Merriwether Lewis, on his way down the Ohio to pick up his companion, William Clark, in preparation for the Lewis and Clark expedition, found so many of them in the water that he used his trained Newfoundland to plunge in, catch them, and bring them aboard the boat, where they proved ‘when fryed a pleasant food.’

Boatmen near Marietta found the river ‘completely overrun with immense quantities of black and gray squirrels.’  They climbed fearlessly up the oars to rest on the boats, which sometimes had five or six of them aboard at once.  Since about a third of the little animals drowned before they reached the other bank, travel was sometimes unpleasant because of ‘thousands of dead squirrels putrifying on its surface and its shores.’

On land, a hunting party could easily bring in several hundred squirrels at once, and kills of one or two thousand are sometimes reported.  Kentucky riflemen scorned random shooting at these tiny, lively targets.  There was a local Kentucky joke to the effect that a squirrel was inedible unless shot squarely through the left eye.  Some hunters shot squirrels only through the eye and that only when they saw them in the highest treetops.  Really distinguished woodsmen like Daniel Boone refused to shoot the little animals at all.  They preferred  ‘barking off the squirrel,’ that is, putting a bullet into a branch exactly at their feet.  Audubon, for whom Boone gave a demonstration, wrote ‘The whip-like report resounded through the woods, and along the hills in repeated echoes.  Judge of my surprise, when I perceived that the ball had hit the piece of bark immediately beneath the squirrel, and shivered it into splinters, the concussion produced by which had killed the animal and sent it whirling through the air.'”

J.J. Audubon’s painting of what he called the migratory squirrel–Scirius migratorious.  He incorrectly believed it was a unique species, but it was actually the same species as the common gray squirrel.

Massive squirrel migrations were so common during the early 19th century that J.J. Audubon mistakenly believed migrating squirrels were a distinct species.  We now know mass migration is an occasional habit of the gray squirrel.  Mass squirrel migrations stopped occurring following the felling of the old growth timber by the late 19th century, but they still happen on a much smaller scale.  The last recorded squirrel migration occurred in 1998 and took place in Arkansas and some adjacent states.  There was also a squirrel migration in 1968 on the eastern seaboard from Maine to North Carolina.  The squirrels migrate in all different directions, unless they are crossing a major body of water when they all head in the same direction.  The migrations last 4 weeks and always occur in September–a time when food is normally abundant.

Scientists don’t know for sure what caused these massive squirrel migrations, but Van Flyger, a retired scientist, put forth a strong logical hypothesis in 1969.  Recent squirrel migrations occurred in poor mast years that immediately followed good mast years.  During the good mast years when acorns are abundant, gray squirrels produce 2 litters.  Normally, in September, gray squirrels disperse to new ranges because early fall is when food is most abundant and young squirrels have an easy time establishing a new territory.  This is known as the “autumn reshuffle.”  The movement is influenced by the amount of mast the squirrels spend time burying.  They stay in the same territory when they experience the spent time there storing food.  But if there is an excess of young and a shortage of food, the overpopulation of squirrels will just keep dispersing across the landscape.  It’s the normal autumn reshuffle on steroids.  The squirrels keep moving because there is not enough mast for them to spend a long enough time in the same vicinity to establish a territory.  They must have a kind of biological clock that tells them to stop dispersing because they’ve buried enough acorns in 1 area to keep them alive for the rest of the year.

There is an evolutionary advantage to this dispersing habit.  Populations of gray squirrels from different geographical regions come into contact and breed, resulting in healthy genetic recombinations.  Moreover, beneficial mutations are retained.  This dispersal strategy explains why gray squirrels are of a uniform color (with some exceptions) whereas fox squirrels (Scirius niger) are not. (See https://markgelbart.wordpress.com/2012/07/05/colorful-fox-squirrels-were-they-the-more-common-squirrel-in-the-southeast-during-the-pleistocene/)  Fox squirrels do not disperse across the landscape, explaining why this species of squirrel only occurs locally, and why it sports so many different color variations.  I think it also explains why fox squirrels are absent from so many regions in the south.  After forests across the south were clear cut, dispersing gray squirrels were able to recolonize young forests while fox squirrels were only able to occupy small areas of remnant woods, perhaps where lumber operation left some trees standing.

Gray squirrel migrations undoubtedly occurred during the Pleistocene.  The nut burying habit of both gray and fox squirrels necessarily evolved to protect their food supply from foraging megafauna and passenger pigons, both of which could sweep a forest clean of mast.  Red squirrels (Tamiascuirius hudsonicus) also store food but rather than burying the mast, they collect it in large caches within hollow snags.  Squirrels still had to share buried acorns with bears and peccaries, animals that like squirrels, can detect the scent of underground food.  But they did successfully hide food from bison, deer, and pigeons.

On a side note I did see another example of interesting gray squirrel behavior yesterday.  A gray squirrel advancing into my yard while traveling on a tree branch kept waving its tail and pausing.  It was waving its tail to attract the attention of potential predators, then looking around to detect their presence.  The tail-waving is a smart strategy that gives them time to take evasive action, if there is a predator present.  Lately, a pair of red shouldered hawks have been hanging around my yard, and my cat killed a juvenile squirrel last week, so it was understandably cautious.

Colorful Fox Squirrels–Were they the More Common Squirrel in the Southeast During the Pleistocene?

July 5, 2012

The extinction of the megafauna saddens me.  America’s wilderness areas are devoid of mammoths, mastodons, ground sloths, and so many other animals, and an ungodly long drive is required to see the remaining species such as bison and elk, unless a person is lucky enough to live somewhere near Yellowstone National Park or in Alaska.  But at least squirrels and rabbits are still abundant in most places.  They are every bit as interesting as the extinct species of megafauna and during the Pleistocene the total biomass of smaller animals probably outweighted that of the larger beasts, so they were common then too.

Tree squirrels are relatively rare in fossil sites because they live in wooded habitats.  When they die, their bodies mix with acidic leaf litter which dissolves bones, if a scavenger doesn’t come along and munch them down first.  Thanks to predatory birds, squirrel fossils do occur in cave deposits.  Hawks and owls capture squirrels, carry them to roosting sites in caves, and often sloppily drop pieces of squirrel where the cave environment preserves them.  Yarbrough Cave in Bartow County Georgia yields the remains of 5 squirrel species–woodchucks, chipmunks, gray squirrels, fox squirrels, and 13-lined ground squirrels.  This cave deposit dates to the Last Glacial Maximum (~20,000 BP carbon date average based on 4 sample dates).  The variety of squirrels is evidence of a diversity of habitats.  Gray squirrels prefer young dense forests; fox squirrels like open mature woodlands; chipmunks inhabit boulder-strewn woods; woodchucks live in open meadows; and 13-lined ground squirrels are denizens of prairie.

Although Pleistocene environments in Georgia consisted of many constantly changing stages of succession, I think 0pen mature forests would have been the most common type.  Frequent fires, megafauna foraging, insect infestation, tree diseases, windthrows, and drought eventually convert dense young forests into open parkland environments with widely spaced large older trees lucky enough to survive the ravages of nature.  Gray squirrels are more common today in Georgia because young dense forests predominate, following the clear cutting of yesteryear.  These squirrels escape predation by jumping from tree to tree which is possible in forests with closely spaced trees, but bigger clumsier fox squirrels run along the ground to reach the safety of a tree.  They’re better adapted to open forests.  Therefore, fox squirrels may have been the more common squirrel of the late Pleistocene in the upper south.  (Fossil evidence suggests they didn’t arrive in Florida until very late in the Pleistocene.)

This fox squirrel was recently spotted in Ringgold, Georgia which is in the northern part of the state where fox squirrels are said to be rare to absent.  This proves they still live in this region.  The lady who took this photo didn’t know what this animal was and posted it online.  Notice to college biology students searching for a thesis idea:  No recent study has been conducted on fox squirrel populations in Georgia.

Mounted fox squirrel killed by a hunter in Georgia.  I lifted this and the following photos from the Georgia Outdoor News forum.  Check out their political forum.  They aren’t exactly open to progressive politics. 

Another mounted fox squirrel killed in Georgia by a hunter.  Note the orange color phase.  Fox squirrels in northeastern Ohio are orange but have no white marking on their nose.  Fox squirrels are locally common on the southeastern coastal plain.

 

 

Note all the color variations on these fox squirrels killed in just 1 locality on the South Carolina coastal plain.

In present day Georgia and South Carolina fox squirrels occur locally on the coastal plain.  They are reportedly rare to absent in the piedmont and mountains, though the the top photo proves they’re not extinct in the region.  In the southeast they seem to prefer open pine forests with a few oaks.  Curiously, in the midwest they’re restricted to hardwood forests.  On average they weigh twice as much as gray squirrels and come in a much greater variety of colors.

I grew up in Niles, Ohio, a small town in northeastern Ohio.  Big orange fox squirrels were the only kind of squirrel I ever saw there.  Our house was surrounded by an oak-dominated woods on 2 sides.  Unlike the orange color phase of southeastern fox squirrels, the ones in Ohio had no white marking on their nose.  I also saw gray and black fox squirrels at a park next to Niagara Falls.  In Georgia I’ve only seen a fox squirrel once.  It was a black one among a dozen gray squirrels poaching pecans in a Burke County orchard.  They are reportedly common on golf courses in the South Carolina coastal plain.  I haven’t seen a fox squirrel in 20 years.  I’m trying to determine how I can find some time to scope this species out on a beach trip next month.