Posts Tagged ‘indigo snake’

Extralimital Species of Pleistocene-aged Turtle Remains Found in the Upper Coastal Plain of Alabama

August 21, 2015

George Phillips wrote his Masters Thesis about Pleistocene-aged, non-mammalian, vertebrate remains found in creeks that flow through the Alabama and Mississippi upper coastal plain, a region also known as the Black Prairie.  Turtle shells are by far the most abundant remains found here because of preservational bias.  Turtle shells are very durable, helping protect the reptile while they are alive.  This durability also makes turtle shells more likely to survive the ravages of time when the bones of most other vertebrates disintegrate.  The results of his study show that several species of turtles have experienced interesting range redistributions since the end of the Ice Age.

Map of Alabama highlighting Dallas County

Dallas County, Alabama.  Bogue Chitto Creek, located in this county, yields many Pleistocene fossil remains.

Blanding’s turtle (Emboidia blandingii) is an endangered species presently restricted to the upper Midwest and parts of New England.  Most of this species’ present day range was under glacial ice during the Ice Age and thus uninhabitable.  Remains of Blanding’s turtle can be found in Pleistocene deposits as far south as the Black Prairie region in Alabama.  The presence of this species in Alabama suggests much cooler summers in the south during the Ice Age (though winters may have been as mild or just a little cooler than those of today). Blanding’s turtles may be unable to endure the long hot summers of the present day south, and this may be the limiting factor on their range today.

Blanding’s Turtle occurred in Alabama during the Ice Age but no longer ranges this far south.

Map of Blanding's Turtle

Present day range of Blanding’s turtle.  During the Ice Age about 70% of this territory was under glacial ice.

The wood turtle (Glyptemys insculpta) is another species of turtle with northern affinities that lived in Alabama (and other parts of the south) during the Ice Age.  This species may also be unable to survive long hot summers.

Plastron of an adult male.

Wood turtle.

Present day range map of the wood turtle.  During the Ice Age >90% of this range was under glacial ice and this species retreated south.  Longer hotter summers chased them back up north.

The only known Pleistocene-aged specimen of a musk turtle (Sternotherus carianitus) was found in Catalpa Creek, Alabama. Today, this species occurs to the west of this site.  Its rarity in the fossil record is unexplained and is probably just due to chance.  During the Pleistocene it apparently ranged further east than it does today.  Any number of unknown reasons could explain its extirpation from the most eastern parts of its range–disease, excessive egg predation, or competition with other species of turtles.

File:Carapace Sternotherus carinatus.JPG

Musk turtle.

Present day range map for musk turtle.  They formerly ranged a little further east during the Pleistocene.

There are 3 species of red-bellied turtles.  The Florida red-bellied turtle (Pseudemys concinna) is presently restricted to peninsular Florida, but Pleistocene-aged remains of this species have been found in Bartow County located in north Georgia.  The Alabama red bellied turtle (Pseudemys alabamensis) is presently restricted to extreme southern Alabama and Mississippi.  The red bellied turtle (P. rubriventris) is presently restricted to the mid-Atlantic states, but Pleistocene -aged remains of this species have been found in the upper coastal plain of Alabama.  It’s likely these 3 species of red-bellied turtles diverged from 1 continuous population that existed before the Pleistocene-Holocene transition when for some unknown reason they became geographically isolated into their present day ranges.  Their curious range distributions beg for a study of their molecular DNA.  The 3 present day species represent a speciation event that may have occurred as recently as 10,000 years ago.  I can’t determine why red-bellied turtles were extirpated from regions in between their present day ranges.  Did overharvesting by humans play a role?

Present day range map for the mid-Atlantic red-bellied turtle (Pseudemys rubriventris)  Remains of this species have been identified from Alabama.

Range map for Alabama red-bellied turtle.  The Pleistocene/Holocene transition was likely a speciation event that caused the 3 species of red-bellied turtles to diverge.

An extinct Pleistocene subspecies of box turtle (Terapene Carolina putnami) was common in Alabama’s coastal plain.  It was larger than present day box turtles but otherwise was similar.  There is no direct evidence of gopher tortoises (Gopherus polyphemus) from the Black Prairie region during the Pleistocene, but a Pleistocene-aged specimen of an indigo snake was found in Bogue Chitto Creek located about 40 miles north of the present day range of this tortoise.  Indigo snakes depend upon gopher tortoise burrows for shelter, so the presence of this snake suggests the presence of gopher tortoises nearby.  Gopher tortoises require sandy soils for burrowing.  They don’t burrow in the heavy upland clay soils so widespread in this region, but they may have burrowed in the alluvial (streamside) sands by the creek.  Gopher tortoises require open environments where they can feed upon short sun-loving plants.  The closure of the forest canopy would have caused their extirpation here.

Two scutes of the extinct giant tortoise (Hesperotestudo crassicutata) were found in this region.  Scientists puzzle over the co-existence here of the cold adapted wood turtle and Blanding’s turtle with the giant tortoise, a species they assume required a frost free environment.  I disagree with their assumption.  I hypothesize giant tortoises were capable of surviving freezing temperatures by either burrowing underground, like their closest living relative (the gopher tortoise), or by utilizing burrows dug by giant ground sloths. If giant tortoises could survive mild frosts as I believe, this species could have co-existed in the same region as cold-adapted species of turtles.  However, it’s just as likely their remains represent a warm climate phase, temporally distinct from when wood turtles and Blanding’s turtles roamed the creek bottoms.  As far as I know, none of these specimens has been radio-carbon dated.

Species of turtle remains found in Pleistocene deposits here that still occur in the region include snapping turtle, alligator snapping turtle, spiny softshell, stinkpot, painted, slider, and Alabama map turtles.

Reference:

Phillips, George

“Paleofaunistics of Non-mammalian Vertebrates from the Late Pleistocene of the Mississippi Black Prairie”

North Carolina State Masters Thesis 2006

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The Orianne Indigo Snake Preserve

May 1, 2013

It’s too late to save most of North America’s megafauna.  Man overhunted most of the magnificent animals on this continent into extinction thousands of years ago, and Europeans nearly eradicated the rest within historical times.  But it’s not too late to save an apex predator of the southeastern coastal plain–the indigo snake (Drymarchon couperi).  A private charitable group, the Orianne Indigo Snake Society, is purchasing land and negotiating with other large landholders to manage their property for the benefit of this snake.  Their goal is to protect 48,704 acres of land within the Orianne Indigo Snake Preserve.  Presently, they own 2,607 acres and have permission to manage an additional 8,678 more acres (mostly owned by lumber companies) for the benefit of the snake.  This seems like a lot of land, but male indigo snakes require as much as 3000 acres of habitat because they are top predators, in fact predators of predators.

Images from the Orianne Snake Society website.

The preserve is located along the Ocmulgee River where there are many sandhills.

Indigo snake range map.  They were extirpated from Alabama decades ago.

Orianne Society volunteer with an indigo snake.  Strippers like to use indigo snakes in their acts because they are long and docile, seldom biting humans.  It’s the largest North American species of snake.

Indigo snakes require 2 different types of habitat.  During winter they den in gopher tortoise burrows located in open pine savannahs with sandy soils, but during summer they forage in shaded bottomland swamps.  They need access to both environments unobstructed by manmade structures, such as busy roads where automobiles take a heavy toll.  Modern day development makes areas with vast acreages of both types of habitat rare.  Moreover, open pine savannahs have been replaced with pine tree farms which are inadequate habitats for gopher tortoises.  Indigo snakes can survive on pine tree farms without gopher tortoises, as long as the lumber operators leave refuse piles for the snakes to seek refuge during colder months.  Indigo snakes also make use of armadillo dens and hollow logs.  The Orianne Society manages habitat by conducting prescribed burns which improve habitat for gopher tortoises, and by encouraging lumber operators to leave debris piles.

Indigo snakes were extirpated from Alabama.  Indigo snakes are a major predator of venomous snakes, and copperhead populations skyrocketed in Alabama, since indigo snakes disappeared there.  The Orianne Society has a captive breeding program.  Two years ago, they began releasing indigo snakes in the Conecuh National Forest in Covington County, Alabama.  Eventually, this may help reduce copperhead populations.

Indigo snakes are primarily forage hunters, though ambush hunting has been recorded.  They actively travel over land and capture other animals, especially snakes.  They bite their prey and thrash and bash the animal into submission.  One study found that 85% of their diet included gopher tortoises, snakes, and rodents.  They are immune to rattlesnake poison and commonly feed upon diamondback rattlesnakes.  They are cannibalistic, so human breeders of captive indigoes keep them in separate enclosures.  They also scavenge.  One was observed feeding on a dead shark, and they will eat fish in captivity.  Scientists suspect indigo snakes feed on fish stranded in shrinking pools during droughts, much like cottonmouth water moccasins do.   Another individual was observed ambushing 5 rufous-sided sparrows by a single puddle when the birds came to drink and bathe.  These behaviors show they are both active and passive feeders.  They’re big eaters despite being cold blooded reptiles.  A species of indigo snake native to Central America was observed feeding on a boa constrictor, then on a jumping viper before the former was digested.

There are 5 species of indigo snakes in the Drymarchon genus.  In addition to the one that lives in North America, 4 species live in Central and South America.  The genus is closely related to black racers.

The Orianne Indigo Snake Preserve protects several species of big snakes.  The indigo snake frequently grows to 7.5 feet long with a record length of 8.5 feet, but this only beats the record length of the coachwhip snake (Masticophis flagellum) by 1.5 inches.   Diamondback rattlesnakes (Crotalus adamateus) have been known to reach a length of 8 feet long, and pine snakes (Pituophis melanaleucus) get to 5 feet long.

Diamondback rattlesnakes grow to 8 feet long but occasionally fall prey to indigos.

Coachwhip snakes get their name because they are shaped just like a whip.  They are almost as long as indigos but are much skinnier.  They come in many different color variations.

Rainbow snakes (Farancia erystrogramma) grow to 3-4 feet long.  These snakes are also found on the Orianne Indigo Snake Preserve.  They burrow in sand and mud in swamps.  They specialize in feeding on eels.

By contrast southeastern crown snakes reach lengths of just 10 inches.  They specialize in feeding upon centipedes.  There are 3 species which diverged following sea level rises that isolated founding populations.

Fort Stewart has some of the best remaining habitat for big coastal plain snakes.  Here, the federal government is free to conduct prescribed burns that improve wildlife diversity, plus there are fewer roads and no real estate development on the base.  Live fire exercises on this and other army bases in Georgia also improve habitat for wildlife by igniting fires.  More species of snakes have been recorded from Fort Stewart than any other area of the state–33 species.  So far, just 21 species of snakes are known to occur on the Orianne Indigo Snake Preserve, but as this area becomes better studied that number will grow.  Fort Stewart is home to bald eagles, wood storks, and healthy populations of wood ducks, fox squirrels, deer, and wild boar.  If this military base is ever closed, I hope it’s protected as a wildlire preserve.

Most North American snakes have been recorded in the Pleistocene and Pliocene fossil records, and scientists think most of today’s existing snake genuses originated early in the Miocene.  Snakes are an ancient part of the ecosystem, and it would be a shame, if we lost any individual species.

References:

Stevenson, Dirk; et. al.

“Prey Records for the eastern Indigo Snake (Drymarchon couperi)”

Southeastern Naturalist 9 (1) 2010

http://www.oriannesociety.org/