Posts Tagged ‘Fox Squirrel’

The Super Squirrel

January 3, 2017

The eastern gray squirrel ( Sciurus carolinensis ) outlasted many of the magnificent extinct species of Pleistocene megafauna because they are well adapted to survive in environments modified by man.  They are just as much at home in suburbs, city parks, and 2nd growth forest of the countryside as they are in the middle of a pristine wilderness.  Unlike western gray squirrels ( S. griseus ), they are not shy around man and will nest in backyards or even attics.  They are nimble squirrels, able to jump from tree top to tree top in the young dense forests that replace abandoned agricultural lands.  And they have a unique way of spreading their populations.  Every September, juvenile eastern gray squirrels begin to expand their range and forage for acorns and nuts.  After they have spent enough time  burying acorns in a certain area, they establish an home range there.  This process is known as the “September shuffle.”  During colonial times when there were still vast tracks of timber, this September shuffle could seem like a massive migration, especially during years of poor mast production following a year of heavy mast production that increased squirrel numbers. (See: https://markgelbart.wordpress.com/2012/08/24/squirrel-migrations/ )

Eastern gray squirrels thrive everywhere they’ve been introduced–England, Ireland, Italy, South Africa, western Canada, and Australia (where they were eventually eradicated by man).  Much to the consternation of English naturalists, they have almost completely displaced native European red squirrels ( S. vulgaris ) on the British Isles.  There are several possible reasons for this displacement.  Eastern grays are carriers of a virus that may be fatal to European red squirrels.  They may also disrupt red squirrel mating and outcompete them for food, and they are simply better adapted to living adjacent to people.  But the most compelling ecological explanation involves comparing European and American Ice Ages.

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The American eastern gray squirrel in Brandon Hill Park, Bristol, England.  Gray squirrels are better adapted to living in deciduous woodlands than native red squirrels and they are displacing them.

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The Eurasian red squirrel is being displaced by introduced American gray squirrels in Great Britain and Italy.

In Europe glaciers covered a greater percentage of territory than they did in North America.  Most of the unglaciated region consisted of grassy or shrubby mammoth steppe with pockets of spruce and pine growing in moist protected areas.  Some southerly lowlands supported more extensive conifer forests.  The deciduous oak forests that dominate most of Europe today were restricted to narrow strips along the Mediterranean coast.  Because glacial stages were 5-10 times longer than interglacials, European red squirrels became better adapted to live in conifer forests.  However, in North America, even during the severest stadials, there were always extensive oak and oak/pine forests that supported large populations of gray squirrels.  Eastern grays evolved the ability to digest acorns better than red squirrels can.  Although eastern grays are not native to Europe, they are a better fit for the interglacial oak forests that exist there today.  Ecological displacement of 1 species by another has occurred thousands of times during earth’s history.  People may object to the displacement of European reds by eastern grays because man played a role in the introduction of the latter, but it is not unnatural or detrimental to the overall ecosystem in this case.

Eastern grays along with California ground squirrels, introduced fox squirrels ( S. niger ), and turkeys are displacing and outcompeting western gray squirrels on the Pacific coast of North America.  All seem to be better adapted to anthropogenic environments.  Western grays are now restricted to deep wilderness preserves.  Introduced eastern gray squirrels are also displacing American red squirrels ( Tamiasciurus hudsonicus ) in British Columbia.

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The American red squirrel is being displaced by gray squirrels in some parts of its range as well.

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Taxidermic mounts of eastern and western gray squirrels. The western is larger with a bushier tail.  Introduced Eastern gray squirrels and fox squirrels, as well as native California ground squirrels and turkeys are outcompeting western grays in suburban areas of California heavily modified by man.

Eastern gray squirrels have co-existed with fox squirrels for hundreds of thousands of years but are more common in many areas, including Richmond County, Georgia where I live.  Eastern grays quickly recolonize agricultural land replaced by dense 2nd growth forest, while fox squirrels prefer mature forests with widely spaced trees.  Because most of southeastern North America was clear cut between 1865-1945, gray squirrels have been quicker to return and spread throughout their range.  Without human introduction fox squirrels may never return to formerly clear cut land.

Eastern gray squirrels boldly live next to people and their unique September shuffle makes them a super squirrel, able to expand their populations and survive where other squirrels can’t.

Reference:

Bruemmer, Corrie; Peter Lurz, Karl Larsen, and John Gurnell

“Impact and Management of Alien Eastern Gray Squirrel in Great Britain and Italy: Lessons from British Columbia”

Proceedings of the Conference on the Biology and Management of Species and Habitats at Risk 1999

 

 

The Cross Timbers Ecoregion. An Analogue for Georgia Environments during Some Stages of the Pleistocene?

June 13, 2012

The cross timbers is a North American ecoregion that exists between the eastern forest and the tall grass prairie.  Much of the cross timbers forest is still intact because the quality of the wood is so poor it was never clear cut.  Acreage never cleared for agriculture but used for pasturage still hosts plenty of really old trees.  400 year old post oaks and 500 year old red cedars are not unknown or even rare.  The cross timbers is also known as post oak/blackjack oak uplands, named for the 2 dominant tree species.  Neither species produces quality wood, explaining why, unlike in the eastern forests, lumber companies left this region alone.

Map of the cross timbers ecoregion.

Oak savannah in the cross timbers.  The flora is influenced by fire, drought, and tornado.  This is the southern part of tornado alley.

The cross timbers ecoregion is bounded by tall grass prairie to the north-northeast, oak-hickory-pine Ozark highlands to the east, and mixed grass plains to the west.  Steep hills, low mountains, rough escarpments, and 4 sizeable rivers shape the topography.  Young forests form impenetrable thickets of scrub oak, greenbrier, and sumac.  Mature forests become oak savannahs, influenced by frequent fire and tornado.  In addition to post oak and blackjack oak, bur oak, and black hickory (Carya texana) grow on the uplands, while big bluestem and Indian grass thrive between the widely spaced trees.  River bottomland forests consist of river birch, mockernut hickory, cottonwood, sycamore, black walnut, hackberry, and buttonbush.  Live oak is a component of the western part of this region.  Red cedar becomes a dominant cross timbers tree when fire is absent or suppressed.

I think the cross timbers region may be a near, but of course not exact, analogue to some parts of southeastern North America during some climatic stages of the Pleistocene, particularly the eoWisconsinian.  The eoWisconsinian is not precisely defined in the literature but generally is thought to be the early stages of the Wisconsinian Ice Age, perhaps roughly dated from 118,000 BP- 70,000 BP.  It encompasses 3 stadials (cold stages) and 3 interstadials (warmer stages).  The climate gradually became cooler and drier during this time period as the north polar ice cap began to reform and expand following its complete dissolution during the Sangamonian Interglacial.  This gradual cooling was interupted by sudden reversals when the climate turned wet and warm.  Temperatures at the beginning of the eoWisconsinian may have been as warm or warmer than they are today, but by the end average temperatures were below those of the present day.

The 3 pollen studies of southeastern North America that date to this time period suggest an environment dominated by oak and grass during interstadials.  The main difference between the Oklahoma cross timbers and the eoWisconsinian of southeastern North America is the considerable presence of pine in the latter, especially during cold stages.  Spruce was present but didn’t become a significant compoenent of southeastern Ice Age forests until after the eoWisconsin.

I also consider the Oklahoma cross timbers an analogue to eoWisconsinian environments of the southeast because of the intermingling of western and eastern fauna.  The fossil record shows that several species of extant mammals and birds today restricted to the west used to live in the south during the Ice Age.

13-lined ground squirrel

Current distribution of 13-lined ground squirrel.  This species lived in the southeast during the Ice Age.

The rangemap above clearly shows the 13-lined ground squirrel (Spermophilus tridecemlineatus) is conspicuously absent from the southeast.  Yet, fossil specimens of this species have been recovered from Yarbrough Cave in north Georgia and the Turtle River in south Georgia–evidence it was widespread in the state during the Ice Age.  Ground squirrels hibernate for an astonishing 8 months.  The evolutionary advantage of being dormant during long winters might explain why they no longer live in south where winters are short.  However, the growing season in the Oklahoma cross timbers is over 7 months long.  I hypothesize its absence in the south today is due to a severe reduction in southeastern grasslands in the early Holocene when forests expanded. Later,  Indians regularly began setting fires here to enhance grassland development, but ground squirrels have been unable to recolonize the area.  It would be interesting to do a little experimental human- aided transport to see if they could live in the present day south on suitable habitat, but I’m sure ecologists would consider it an invasive species and object.  Along with ground squirrel specimens, other western species such as badger, northern raven, upland sandpiper, and magpie fossils often turn up in southeastern fossil sites dating to the late Pleistocene.

Fox squirrels are far more common in the cross timbers than gray squirrels.  The latter prefer dense young forest where they can jump from tree to tree to avoid predators.  Fox squirrels are larger and less agile and prefer to run on the ground between widely spaced trees when escaping predators.  Therefore, I hypothesize they were the more common squirrel in Georgia’s interstadial oak and grass savannahs.

Specimens of hog-nosed skunk (Coneputus mesoleucus) appear in some Georgia and Florida pleistocene fossil sites, but it too is absent in the present day south.  It’s not even a denizen of the cross timbers but occurs just west of that region in arid habitats.  I hypothesize patchy tracts of desert-like environments persisted throughout the south during most of the Ice Age, expanding during stadials but still existing as relics during interstadials.  The complete disappearance of these desert-like tracts may explain this species more restricted present day range.

Black-tailed jackrabbits, pronghorn antelopes, prairie dogs, and grizzly bears reached their easternmost range limit in the cross timbers during colonial times.  There’s no fossil evidence that jack rabbits and pronghorns ever recolonized the south after the mid-Pleistocene but they did occur in the region in the early Pleistocene and the Pliocene.  Probably, a large forest grew along the Mississippi River, forming an unsuitable ecological barrier that prevented their southeastern recolonization when climatic changes allowed favorable habitat to redevelop there.  Prairie dogs never lived in eastern North America as far as we know, but Pleistocene-age fossils of grizzly bears have been uncovered in Welsh Cave, Kentucky.  Why grizzly bears never colonized the rest of the southeast is a bit of an ecological mystery.

Incidentally, early white explorers reported the cross timbers to be rich in game.  In the early 19th century they saw mixed herds of thousands of bison, mustangs, deer, elk, and pronghorns.  One report mentions a bison herd that was 60 miles long.  In 1823 A.P. Chouteaux shipped the black bears skins of 300 females and 150 cubs from his trading post in northeast Oklahoma in just 1 season.  As late as 1911 a huge 720 lb black bear was killed in the cross timbers region.

Reference:

Claire, William; Jack Tyler, Bryan Glass, and Michael Mares

Mammals of Oklahoma

University of Oklahoma Press 1989

 

Fire Suppression = A Decline in Biodiversity (Part 2–The Animals of Longleaf Pine Savannahs)

June 29, 2011

Fox Squirrels come in several color phases–orange, black, and gray.  Some have white or gray masks as well.

Fox Squirrel–Sciurus niger

I love these big colorful squirrels.  I lived in Niles, Ohio until 1975, and our home was bordered by oak woods on 2 sides.  Big orange fox squirrels were the playful denizens there.  But since I’ve lived in Georgia, I’ve only seen one–a black masked fox squirrel foraging with a group of gray squirrels (Sciurus carolinensis) in a pecan orchard in Burke County.

This range map is bullshit.  No statewide survey of fox squirrels has been done in at least 50 years, if ever.  It’s likely an accurate range map would show a much patchier distribution.

Southern fox squirrels differ in their habitat requirements from northern fox squirrels, despite being the same species.  The former prefer mature longleaf pine savannahs with fingers of oak forests, while the latter thrive in oak/hickory woods.  Fox squirrels are declining in Georgia because longleaf pine savannahs were largely replaced with shorter rotation loblolly pine tree farms.  Lumber companies harvest loblolly pines every 50 years which is not enough time for trees to develop snags.  The Trees are also planted closely and fire is suppressed.  Gray squirrels are more abundant today in state because they’re well adapted to the dense young forests that have sprouted on abandoned agricultural lands.  Gray squirrels escape predation by jumping from tree top to tree top, while fox squirrels prefer to dash on the ground as far as they can before retreating to a tree.  Though clumsy in trees compared to their smaller cousins, their larger size allows them to put up more of a fight, if a predator catches up to them.  This difference in behavior explains why gray squirrels occur in closed canopy forests, and fox squirrels prefer open parkland forests.  For this reason I think fox squirrels were more abundant in this region during the Pleistocene when open environments were common.  Areas managed for red-cockaded woodpeckers should benefit fox squirrels.  Forest managers used longer rotations and fire to maintain the bird’s required habitat.

Red Cockaded Woodpecker–(Picoides borealis)

Photo of a red cockaded woodpecker from google images.  All the photos in this entry are borrowed from there.

Thirty years ago, this bird was on the verge of extinction, despite having formerly been common throughout the south.  Fire suppression and short forest management rotation nearly caused the death of this species.  Young pine trees never develop the soft rot that red cockaded woodpeckers need for boring nesting cavities.  As a defense mechanism, red cockaded woodpeckers constantly peck wells below their nesting cavities from which pine sap continously flows.  The pine resin repels rat snakes–their number one predator.  For this defense mechanism to work, live trees are a must.  And without fire hardwood understory reaches the level of the nesting cavity allowing flying squirrels, and other predators easy access.  Flying squirrels will decimate red cockaded woodpecker nests.

In a successful effort to save the birds, scientists identified habitat requirements and some suitable land was set aside and managed using prescribed burns and longer tree harvest rotations.  Birds were relocated to the best habitat, artificial nesting boxes were installed to supplement the shortage of good nesting trees, and flying squirrel exclusion devices were used.  In many protected areas red cockaded woodpecker family groups (family groups consist of 2-10 individuals) have increased dramatically to the point where it’s no longer necessary to provide artificial nests or to protect them from flying squirrels.  At SRS for example the population grew from 1 family group in 1987 to 30 by 2003.

Sandhill Crane–(Grus canadensis)

These impressive birds grow to 5 feet tall.  They prefer to nest in grassy marshes adjacent to prairies or savannahs.  The real life version of Sesame Street’s Big Bird used to be common, but since grasslands and wetlands have declined so have the birds.  Georgia’s population includes a permanent one consisting of small family groups, and large congregations of winter migrants.  They’re omnivorous feeding on insects, crayfish, mice, snakes, frogs, worms, acorns, fruit, roots, and farmer’s crops.

Bachman’s Sparrow–(Peucaea aestivalis)

Another inhabitant of open pine savannahs that is declining in abundance.  I heard this bird’s song on a youtube video and recognized it as one I’ve heard.  Evidentally, the sparrow still occurs in Augusta.

Indigo Snake–(Drymarchon corais)

This snake grows to 9 feet long, making it the longest serpent in North America.  They’re rare because their habitat has been fragmented, and they need large ranges.  They hunt during the day and retreat into gopher tortoise burrows at night.  A wide variety of prey is taken–other snakes including venemous ones, small mammals, birds, frogs, and fish.  Indigo snakes don’t kill by constriction or envenomation, but instead bite the head of their prey and thrash, breaking the spines of the small creatures.  Their metabolism is faster then that of most other snakes.

Gopher Tortoise–(Gopherus polyphenus)

 

Gopher tortoises depend on a frequent fire regime to spark the growth of the kinds of plant they eat.  They also like sandy soil that makes it easy for them to dig their elaborate tunnel systems.  They’re a keystone species–over 60 vertebrates and invertebrates depend on their burrows for shelter.  (See also my article–“The Giant Extinct Tortoise, Hesperotestudo crassicutata, must have been able to survive light frosts” from my April or March archives)

Popular game animals such as white tail deer, turkey, and quail thrive in longleaf pine savannahs.  Savannahs were a favored habitat of many extinct Pleistocene species as well including mammoth, long horned bison, horses, llamas, Harlan’s ground sloth, hog nosed skunks, giant tortoises, and others.