Bull Sharks (Carcharhinus leuceus) in Fresh Water Rivers

Not long ago, Noel Todd caught an 8 foot long, 368 pound bull shark in Shell Creek which is located in Valona, Georgia.  Shell Creek is a brackish stream not far from the coast, so it’s not shocking that a shark  might be found here.  However, bull sharks have been sighted 2500 miles up the Amazon River.  The North American inland shark-catching record was set in 1937 when 2 fishermen caught a bull shark in the Mississippi River next to Alton, Illinois.

“Nearly comatose” bull shark discovered in Lake Pepin, Minnesota which is connected to the Mississippi River.  This is the lake where Laura Ingalls’ father (of Little House on the Prairie fame) used to fish.  Bull sharks are tropical to semi-tropical species, not well adapted to such cold waters.  I discovered 15 months after posting my article that this photo is an APRIL FOOLS JOKE.  I was fooled and I apologize to my readers.

The bull shark that Noel Todd caught in Valona, Georgia in a  brackish water tidal inlet.

In Georgia before the dam that created Lake Seminole was built, bull sharks used to congregate in the Chattahoochee River adjacent to a beef processing plant above Albany where the factory dumped the offal into the water.  Bull sharks are common in 2 freshwater lakes that have access to an oceanic outlet–Lake Nicaragua in Central America and Lake Pontchartrain, Louisiana.

Unlike most species of sharks, bull sharks are capable of living in freshwater because their kidneys with the aid of a special gland help them retain salt.  Most other species of sharks don’t have the physiology to be able to withstand long exposure to freshwater.  Other species of sharks would suffer cell edema if trapped in freshwater, and they would die.  The ability to survive in freshwater gives bull sharks a tremendous advantage over other shark species.  Bull sharks are a shallow water species that live in coastal waters.  The females give birth to 1-13 live pups which often travel to freshwater rivers where they immediately become a top predator.  Instead of being vulnerable prey like most juvenile marine life, they top the food chain.  They simultaneously avoid predators, while gaining access to a bounty of prey items.  This may also help them avoid cannabilistic adults of their own kind.  Most of the young pups stay in brackish waters and return to the ocean when they grow larger.  Scientists don’t know why a few swim great distances up freshwater rivers, but I believe that behavior is influenced by a random mutation that could potentially lead to a beneficial adaptation.

Bull sharks account for more attacks on man than any other shark species, probably because they’re a coastal species more likely to come into contact with people.  It was probably this species that inspired Peter Benchley to write Jaws. Five shark attacks that occurred along the New Jersey coast in 1916 provided the plotline for his classic story.  Two of the shark attacks occurred in Matewan Creek–16 miles inland. 

Bull sharks get their name from their habit of attacking and eating other sharks, making them a bully among sharks.  They also feed upon fish, rays, shrimp, crabs, sea snails, turtles, carrion, and garbage.  They’re considered a near threatened species which is not surprising since the entire ocean has pretty much been overfished.

Bull sharks are not the only primarily salt water species of fish found way up freshwater rivers.  Flounder, hogchokers, mullet, tarpon, and needlefish expand their range from brackish water and swim into the freshwater of the middle Savannah River basin every summer.  I’ve never had the opportunity to fish in a brackish segment of the a river but it must be interesting.  Largemouth bass, gar, and catfish are common freshwater species found in brackish waters where they swim alongside bullsharks, mullets, and flounder.

Hog chokers, a type of flounder, swim into the middle Savannah River every summer.

Needlefish–another saltwater species that spends summer vacations in the middle portion of Georgia’s freshwater rivers.

Mullet–a great tasting meaty fish that schools up freshwater rivers.  I used to catch these with a cast net in the ocean off Harbor Island, South Carolina.

The pristine waters of the Pleistocene must have held exponentially more fish then those of today, but modern day damming, overfishing, and pollution have decimated fish populations.  Bull sharks likely swam way up freshwater rivers during the Pleistocene, but the odds of finding a fossil bull shark’s tooth hundreds of miles inland must be very low.  Bull shark’s teeth have been found at the Pleistocene-aged Isle of Hope site but this is on the coast in Chatham County.

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Squirrel Migrations

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.

Is the 9-banded Armadillo (Dasypus novemcinctus) a Dwarf Mutation of the Pleistocene Species, Dasypus bellus?

A couple of weeks ago, I drove on Highway 56 in Augusta, Georgia and saw a live armadillo roaming a damp meadow adjacent to a creek bottom.  The setting sun and rising mist from a recently expired thunderstorm seemed like an appropriate atmosphere to witness this Pleistocene relic.  This was the first occasion I’d ever seen a live armadillo, though road-killed individuals are a common sight during summer when they become active at night.  Alarmed armadilloes jump vertically–an effective  defense mechanism that thwarts big carnivores but it is a disaster if the danger is a passing car, straddling the dumb creature.

9-banded armadilloes–now common from the coastal plain of the southeastern U.S. south to South America.

9-banded armadilloes are members of the Xenarthan order of mammals, also known as the edentates.  The species in this order have teeth with no enamel.  The Xenarthan order includes sloths, anteaters, and the extinct glyptodonts as well as armadilloes.  Armadilloes eat insects, grubs, and worms; and therefore require mild, moist climates where that kind of food is available year round.  Southeastern North America provides plenty of mesic habitats and soft soils favorable for this species.  Armadilloes survive hot summer days and cold winter nights by digging narrow burrows that shelter them.  Because they are relatively primitive mammals with low metabolic rates (almost like reptiles), they have difficulty maintaining a constant body temperature, and extreme temperatures, especially hard frosts, can kill up to 80% of the population. 

Mother armadilloes give birth to 4 identical clones from 1 egg, making them a particularly interesting creature for scientific study.  Scientists use armadilloes as lab animals to study leprosy because they’re one of the few animal species other than man that is susceptible to the bacteria responsible for causing leprosy.  The leprosy thrives in armadilloes due to their low body temperatures.

9-banded armadilloes have been expanding their range into North America since about 1849.  They were reported in south Texas during the mid-19th century and some were introduced into south Florida circa 1921.  Now, they are well established across the southeast as far north as the piedmont region, but they are restricted to creek bottoms with soft soils.  During the Pleistocene the beautiful armadillo (Dasypus bellus) apparently was common in eastern and midwestern North America.  Specimens of this extinct armadillo have been found in just about every Pleistocene fossil site in the southeast, and their remains have also been recovered from as far north as Indiana.  According to the scientific literature, the supposedly extinct beautiful armadillo was anatomically very similar to the 9-banded armadillo.  Sometimes the word,” identical,” is used to describe the comparison.  The main difference is size–the Pleistocene species was on average twice as big as the modern species.  Dasypus bellus became extinct probably between ~10,000 BP-~7,000 BP.  I hypothesize that Dasypus bellus and Dasypus novemcinctus are the same species.

Dasypus bellus–the supposedly extinct beautiful armadillo.  Note it is also 9-banded.  I propose it’s the same species as the modern day 9-banded armadillo which is nothing other than a dwarf mutation of this Pleistocene species.

I propose that following man’s extermination of the megafauna, the paleo-indians began to rely more on small to medium-sized animals for protein.  Men intensified their predation on Dasypus bellus–its leathery armour was no match for human ingenuity.  Men became expert in locating armadillo burrows, pulling the animals out, and dispatching them.  I think man caused the extinction of Dasypus bellus.  There is no known climatic event within the last 12,000 years that could have caused their extinction from southeastern North America, and it’s almost certain there were no unusual cold waves in Central America.  However, somewhere in South or Central America, a dwarf mutation of Dasypus bellus occurred.  Dasypus novemcinctus is practically unknown from Pleistocene fossil sites (I think 1 specimen is reported from the literature).  I believe Dasypus novemcinctus is simply a recent dwarf mutation of Dasypus bellus. Because of its smaller size, Dasypus novemcinctus reached breeding age earlier than Dasypus bellus.  Faster breeding allowed Dasypus novemcinctus to survive human hunting pressure.  This species is now in the process of recolonizing its former range–an interesting example of evolution that has occurred within written historical times.  Some scientists propose that this recolonization is occuring because man has reduced the population of natural predators, but this is implausible because 9-banded armadilloes originated from a geographical area where jaguars, cougars, and Mexican gray wolves abounded.

A recent DNA study supports my hypothesis.  Brandon Letts and Betti Shapiro were able to recover DNA from a fossil specimen of Dasypus bellus. They compared this DNA with Dasypus novemcinctus DNA and concluded  the 2 species showed a “surprisingly close relationship.”  Surprisingly close enough to be considered the same species?  DNA studies along this line are in their infancy.  I hope more studies like this are on the way.

Rapid evolution of size among the Xenarthan order is well documented in the scientific literature.  Dr. Hulbert of the University of Florida catalogued the changes in size between presumed ancestral and later species of Xenarthans.  It’s astonishing to see that the average length of the femur from a northern pampathere ( Holmesina floridanus–a species of extinct giant armadillo) went from 20.3 cm during the late Pliocene to 25 cm during the Irvingtonian Land Mammal Age of the mid-Pleistocene (when it evolved into Holmesina septentrionalis) to 33.2 cm during the late Pleistocene Rancolabrean Land mammal Age.  The same size increases were found for giant ground sloths, glyptodonts,  and the beautiful armadillo.  The size increases likely evolved as a naturally selected defense against predation.  The larger individuals were more likely to survive attacks from carnivores.  In the case of Dasypus novemcinctus the environment has naturally selected for a size decrease that fostered faster breeding.

The Northern Pampathere–Holmesina septentrionalis

Jaw bone of the extinct northern pampathere–an armadillo that grew to the approximate size of a bear.

In addition to Dasypus bellus an even larger species of armadillo lived during the Pleistocene in Florida, the coastal plain of Georgia and the Carolinas, Texas, Louisiana, and southern Arkansas.  It was 3 feet tall, 6 feet long, and weighed up to 500 pounds.  In Georgia its fossil remains were found at the Mayfair site in Chatham County, and in South Carolina its fossils have been found at Edisto Beach and 2 other coastal sites.  To sustain its size, it likely ate more plants than invertebrates.  Glyptodonts, distant relatives of armadilloes, occurred within a similar geographic range.  They grew to the size of a small car.

South American Species of Armadilloes

Over 20 species of armadilloes live in South America .  Here are photos I found online of 3 interesting species.

The giant armadillo (Priodontes maximus) found in the Amazon jungle.  It can weigh up to 130 pounds.

The screaming hairy armadillo (Chaetophroctor vellerusus).

The Pink Fairy Armadillo (Chlamyphorus truncatus).  Looks like something from the Star Trek episode, The Trouble with Tribbles.

References:

Letts, Brandon; and Betti Shapirl

“The Recovery of Ancient DNA from Dasypus bellus Provides New Possiblities for Investigating Late Pleistocene Mammal Response to Climate Change”

ECU General Assembly Abstract May 2010

Mcdonald, Gregory H.

“Paleoecology of Extinct Xenarthans and the Great American Biotic Interchange”

Bulletin of the Florida Museum of Natural History 2005 45 (4) 313-333

A Geriatric Saber-tooth and Other Odd Vertebrate Fossils

Many vertebrate fossils look familiar, even to laymen.  The average man on the street could identify the complete reconstructed skull of a Smilodon.  Other relatively common fossils are so easily recognizable that the amateur novice fossil collector can quickly learn to ID them.  It’s not hard to discern the difference between a mammoth and mastodon tooth, and after a little practice the difference between a horse and tapir tooth is quite apparent.  Size alone makes bones such as a femur of a proboscidean distinguishable from that of a bison.  But the chances are just as likely that a fossil collector will stumble upon a bone so odd it creates a mystery.  The hyoid bone is one example that without consulting a book, I’d never be able to identify.

A comparison of hyoid bones from 3 closely related species of proboscideans–Africans elephants, Indian elephants, and Columbian mammoths.  The hyoid bone is the tongue bone.

A Neanderthal hyoid bone.  About a dozen muscles including the tongue are attached to it.  It’s more often found with one of the ends broken off.

Who besides a medical doctor or trained vertebrate paleontologist would have thought this bone rests a few inches above the pharynx?  Usually, only half of this u-shaped bone is found, and it resembles an erect penis.  A dozen muscles are attached to this bone including the tongue, so in laymen’s terms it can be known as the tongue bone.  Howler monkeys may have the largest hyoid bones in the animal kingdom.  It makes the area below their chins ovoid in shape, and it aids the high volume of their howls.

Howler monkeys have big hyoid bones.  Situated above the pharynx, it contributes to the monkey’s ability to loudly vocalize.

Other odd fossils may be hard to ID, simply because they’re  so nondescript.

Woolly Mammoth heel bone (Calcaneum).

The calcaneum or heel bone looks like an uninteresting rock.  In the living animal it’s attached by ligaments and tendons to the astralagus or ankle bone which is much more interesting to examine.

Camel astralagus or ankle bone.

Many fossils are unusual due to morphology.

Giant ground sloth bone with a puncture mark made by a big cat of some kind.

The above fossil is interesting because of the cat canine puncture mark on it.  A big cat either killed this baby ground sloth or scavenged it.  Cats eat fresh kills far more often than they scavenge.  It seems likely the cat killed this unfortunate animal.  How did it get past the mother ground sloth?  Adult ground sloths were much larger than any cat species, and had claws and armoured hides under thick fur.  I’m sure the mother wouldn’t give up their offspring without a fight.  Perhaps, the young sloth wandered too far from the protective vicinity of its mother.  Which species of cat did the damage?  I say jaguar, but the scientists who examined the specimen believe it was a scimitar tooth (Dinobastis serum).  Jaguars have a more powerful bite and their canine can easily puncture bone.  The fanged cats didn’t have as powerful a bite–I’m not sure it would’ve punctured bone.  But if it is from the scimitar-tooth, we are looking at the results of a confrontation between 2 extinct mammals never to be seen again.

Many vertebrate bones also show evidence of invertebrate activity.  A fossil collector gave me a piece of a dugong bone with holes made by burrowing clams. (See https://markgelbart.wordpress.com/2010/04/  It’s the third article down in the April 2010 archives.) Terrestrial vertebrate bones occasionally have holes made by burrowing beatles.  Vertebrate bones with this kind of morphology are evidence the fossils rested on top of the ground or within topsoil for years.

Smilodon Vertebrae fused together from arthritis.

The photo above shows that a tough old Smilodon, aged enough to develop arthritis, still survived for years despite its ailment.  A high incidence of severe injuries occurred among the population of saber-tooths that left specimens found in the La Brea tar pits.  Apparently, these big cats wrestled large, heavy-bodied prey to the ground before killing the beast by slicing through the soft throat with their fangs.  They often suffered the kinds of injuries a human might get from lifting too much weight.  But they survived these debilitating injuries, suggesting to some scientists that they lived in prides and took care of each other.  However, other scientists think they were not social animals for 2 reasons: they have relatively small brains compared to those of lions, and the vast majority of cat species are solitary.  I agree with the those who think Smilodon was a solitary species.  I think saber-tooths could survive serious injuries because even a partially crippled one was more than a match for most other carnivores, and they could drive them from their kills, not unlike the way Clint Eastwood chased away young punks in his movie, El Camino.

The Savannah Wildlife Refuge

Until the late 18th century a vast cypress swamp covered the area just north of Savannah, Georgia, a city founded in 1704 by General Oglethorpe. Plantation owners had cultivated rice in the South Carolina low country for a century before they cleared the cypress swamp north of the then young metropolis of Savannah.  In the process they completely converted the landscape from deeply wooded swamp to a virtually treeless marsh.  The end of the Civil War also brought an end to rice cultivation in this region because the freed slaves left, and the white plantation owners didn’t know how to farm rice.   The rice fields gave way to freshwater marshes that became a haven for wintering waterfowl.  In 1927 the federal government bought the land and declared it a National Wildlife Refuge.  Federal maintenance workers still operate the rice field trunks that control the flow and level of water for the benefit of wild plants.  The aquatic vegetation provides a bounty of food for wintering ducks.

Recess Plantation Trail.  It’s over 3 miles long and is simply an old rice dike.  Birdlife abounds.

Vegetation is lush and includes giant cutgrass, giant plume grass, wild rice, cattails, bamboo cane, lilly pads, and arrowleaf, among many other species of plants.

A thick stand of arrowleaf (Sagitteria).  Also known as duck potato, in the fall and winter it produces an underground tuber that allegedly tastes similar to new potatoes.  It was an important food of Native Americans.

The SWR also protects a still extant cypress swamp on the Georgia side of the Savannah River, but this part is accessible only via boat.  Last Monday, I visited the readily accessible South Carolina side.  The 4 mile long Laurel Hill Wildlife Drive is a road that crosses the top of an old rice dike.  Lush, year round vegetation grows in the wet fields.  The flora is dominated by giant cutgrass, giant plume grass, cattails, wild rice (yes, the edible gourmet grain), and arrowleaf.  I was going to harvest some wild rice, but it grows in deep water surrounded by alligators.  (It wasn’t until after I read the visitor center’s brochure that I realized harvesting plants was against refuge rules.)  Many of the aquatic plants are edible for humans as well as birds. 

Even though I visited the refuge at a bad time of day and year, I saw lots of birdlife.  The first bird I saw was an especially exciting find–an immature roseate spoonbill (Ajaia ajaja).  The bill on this species is unmistakable, but according to bird guides it lives no farther north than south Florida.  I couldn’t get close enough for a photo, but other birders have seen and photographed this species in South Carolina and Georgia, so it must be expanding its range.  Below is a photo of a roseate spoonbill taken in South Carolina by another birder.

Roseate spoonbills develop pink feathers from eating shrimp.  The immature ones are pure white. It feeds on small animals by using its spoonbill to sift through shallow water.

Swallows (I think tree swallows, but they never stay still enough for positive ID), red-winged blackbirds, and cattle egrets were the most common birds.  I saw several purple gallinules–along with the roseate spoonbill another species I’d never seen before.  Though this chicken-sized rail can fly, they more frequently escape danger by running across lilly pads, diving into water, or climbing into ditch-side bushes.

A purple gallinule (Ionornis martinica).  Click to enlarge and examine the bottom center of the photo.  I saw or heard about 16 species of birds in little over an hour about noon on a hot August day.  The best time for bird-watching in the SWR is during the winter when over 20 species of ducks migrate here.  The flocks attract hunting bald eagles.

Other birds on my checklist for the 90 minutes I was inside the refuge include eastern kingbirds, mourning doves, great egrets, little blue herons, a small unidentified heron or bittern, double crested cormorants, a clapper rail (I think), an unidentified duck, and turkey vultures.

Spanish moss clinging from a live oak.  An island in the middle of the marsh supports a maritime forest of live oaks, palms, and loblolly pines.  This is the only place in the refuge where mosquitoes bothered us.

A live oak  growing on the island.  Grass is growing out of the ancient cistern that rests in front of this tree.  The cistern is the sole surviving relic from the days of rice cultivation.  Archaeologists think gutters from the roofs of 4 slave houses led to the cistern.  The slaves who cultivated the rice lived on the island which is the only dry land in the marsh.  After the Civil War and the collapse of slavery, rice farming in South Carolina died.  No white southerners knew how to cultivate rice.

The only reptiles I saw were 2 alligators, and I could hear bullfrogs.  Reportedly, cottonmouth water moccasins and banded water snakes are common here.

Click to enlarge the photo and look for the 5-8 foot gator swimming in the canal.

Lilly pad covered expanse of water.

I didn’t arrive early enough in the day to see mammals which are more likely to emerge at night, but the refuge is reported to be home for bobcats, mink, otter, raccoons, rice rats, and marsh rabbits.  Habitat such as this artificially maintained marsh would be ideal for some now extinct aquatic species of Pleistocene mammals–giant beavers (Casteroides ohioensis), 2 different species of capybaras (Neochoreus and Hydrochoreus), and mastodons (Mammut americanum).  Fossil specimens from these species have been recovered locally, suggesting that open marsh environments did exist in the region long before men could have felled the cypress swamps.  Dramatic climate fluctuations must have been the primary force creating marshy habitat where cypress swamps later dominated.  I propose that alternating wet and dry climate cycles caused a varying combination of drought, fire, windstorms, and flood, resulting in these pre-historic marshes.  These are not unlike the factors influencing the make-up of the current day Okefenokee Swamp where marshland is interspersed with cypress swamps.

The Laurel Hill Drive Exit.  A park maintenance worker had just mowed here, stirring up insects, and attacting cattle egrets which were one of the most visibly common birds in the refuge.  An extinct species of stork was likely the Pleistocene ecological counterpart to the cattle egret.

Map of the South Carolina part of the Savannah Wildlife Refuge.  Laurel Hill Drive is off 170, not 17 as erroneously reported on other online sites.  Make sure you approach the refuge from Savannah to see the view from on top of the Herman Talmadge memorial bridge.  The refuge from this vantage point looks like an African savannah.

Tybee Island Avifauna

We stayed at the Howard Johnson Hotel on Tybee Island the night before out trip through the SWR.  It gave me a little time to survey the avifauna on this narrow barrier island east of Savannah, Georgia.   Along the beach laughing gulls, herring gulls, and boat-tailed grackles abound.  Mourning doves and dusky seaside sparrows forage in the dunes immediately behind the beach.  This was the first time I’d ever seen the latter species.  The literature states that dusky seaside sparrows (Ammospiza maritima) occupy a narrow niche, living  in salt marshes and beach dunes.  Unlike most species of sparrows which feed mainly on grass seeds, dusky seaside sparrows eat snails, fiddler crabs, and other animal matter.  However, I saw them feeding on sea oat grains.  I surveyed 2 other sea birds–brown pelicans and a least tern (I think).  On the inland part of the island I saw city pigeons, starlings, and a cardinal.

AJ’s Dockside Restaurant 

We ate supper at AJ’s Dockside Restaurant.  It offers a great view of a small dock and a large salt marsh.  Dolphins and schools of mullet are probably often seen in the inlet behind the back patio where we ate, but I didn’t see any.  My fried flounder po’ boy was delicious.  My daughter ordered grilled pork chops.  The chops were good, but I must say they were served with the worst hushpuppies I ever ate in my life.  They were dense and doughy.  Hushpuppies should be light and airy.  AJ’s needs to change the recipe they use for hushpuppies.  Stick to the po’boys.  They’re good and won’t bankrupt you.

View from AJ’s Dockside Restaurant.

Humans Cultivated Figs During the Pleistocene

Israeli archaeologists found the burned remains of a house near the ancient biblical town of Jericho.  The site, named Gilgal 1, is much older than Jericho, dating to 11,400 BP.  They discovered 9 dried figs within the site of the house.  Scientists determined this variety of fig was a cultivated mutant that resulted in a sweeter fruit than any wild fig, and it had no seeds.  Most wild figs requre tiny pollinating wasps but this mutation did not–proof that it must have been propagated by people.  This makes the fig the oldest known cultivated plant, and it predates the known cultivation of cereal grains by thousands of years.  It’s the only known cultivated fruit dating to the Pleistocene.

This variety of fig is known as LSU purple, developed by the Louisiana State University agricultural department.  I grew these in my backyard.  The tree is incredibly productive, but the fruit is only of high quality, if there is little rain during the week they ripen.

Figs are easy to propagate.  Simply cut a 12 inch twig from an existing bush and plant it in a container.  Keep it well watered.  The leaves will die back as the twig grows roots.  Soon, the twig will refoliate and grow into a bush or tree.

My Celeste fig hasn’t been producing in recent years, so I cut a twig from it and planted it in this container last summer.  This is a 1 year old fig sapling.  It should begin producing Celeste figs within the next few years.

I grow 2 varieties of figs.  LSU purple figs are large and as the name suggests, purple.  They produce abundant good quality fruit as long as the weather is dry.  Any significant rain while they are ripening causes the fruit to split open which attracts insects.  This makes them kind of yucky, and the rain also dilutes the sugar content, making them less sweet.  Split figs not invaded by insects are still usable.  Slice them and place them in a simple syrup made from brown sugar and water and boil them for about 5 minutes.  They taste just like canned Kadota figs.  The other variety of fig I grow is Celeste, a small brown fig with a purplish tinge.  This variety is more resistant to splitting from heavy rain.  I find it puzzling that LSU developed a fig so unsuited for the humid environment of Louisiana.  I recomend Celeste over LSU purple, though the latter looks so much better.

My figs attracted 5 species of birds this summer including crows, mockingbirds, cardinals, brown thrashers, and red bellied woodpeckers.  They’re likely drawn to the insects that infest the fruit such as wasps, ants, fruit flies, and stink bugs.  The combination of fruit and insects provides the birds with a balanced diet.

This is a photo of my fig tree with a crow on it.  Click on the photo to enlarge it, and you should be able to see the crow on the upper right side of the tree.  I tried to take a better photo, but crows are just too wary.  I took this photo from inside my home. 

Two species of figs are native to North America but are restricted to a range from central Florida south to the tropics of South America.  Strangler figs ( Ficus aureus and Ficus citrifolia ) have a fascinating life history.  Mature trees produce up to 1 million edible fruits every year.  Birds eat the fruit and deposit the seed in their dung on another tree’s bark.  The fig seeds begin their life as an epiphyte tree parasite and start growing on a host tree (often cypress, oak, or palm).  Eventually, they send roots to the ground and kill the host tree.

A strangler fig that appears to have smothered its host–apparently a live oak.  Now it’s a dead live oak.  Strangler figs depend on a tiny species of wasp (Pegoscapus mexicanus) for pollination.

Strangler figs may have ranged farther north during warm climate phases of the past.  It’s possible strangler figs colonized the Georgia and Carolina coasts during the Sangamonian Interglacial (~132,000 BP-~118,000 BP) which may have remained frost free as evidenced by the presence of giant tortoises.  The early Pliocene and most of the Miocene were also mostly frost free and strangler figs probably colonized the entire southern half of the North American continent.

Figs are in the same family (Moracea) as the mulberry (Morus rubra).  Mulberries were a common fruit of the Indians and formerly grew abundantly in virgin forests.  It’s not endangered but I’ve rarely encountered them.  Perhaps mulberries, a temperate species, evolved from a tropical fruit that grew in North America during the Miocene.

Changing Forest Composition in Northwest Florida over the Past 40,000 Years

Camel Lake is an ancient body of water located 30 miles west of Tallahassee, Florida in Liberty County.  Geologists haven’t been able to determine if it’s a limestone sink lake or an aquifer positioned near the surface of the land.  It’s not a large lake being 500 yards in diameter, and it is sometimes referred to as a pond.  Today, open pine savannah consisting of longleaf pine, turkey oak, and wiregrass surround the lake.  Cypress trees, Spanish moss-covered live and laurel oaks, myrtle, and titi grow adjacent to the water.  In 1986 three scientists took a core of the lake bottom.  They counted pollen grains, catalogued plant macrofossils, and carbon dated differing levels of the core.  The information they gathered provides a diary of changes in plant composition in the vicinity of Camel Lake over the past 40,000 years.

Shoreline at Camel Lake, Florida.  A core of sediment taken at this lake found Pleistocene -aged pollen dating to as old as 40,000 years BP.  They found plant macrofossils in abundance as well including needles resembling those from longleaf pine, leaves similar to those of live oak, a species of quillwort no longer found south of North Carolina, and many other species.

The period of time from ~40,000-~31,000 BP is known as the Mid-Wisconsinian Interstadial.  The climate during this era was at least as wet as today, and maybe more so, because the glacial ice covering much of Canada was in a meltwater phase, and more moisture flowed into the atmosphere.  But it was still the Ice Age and temperatures were slightly cooler than those of today, reducing evaporation rates.  The cooler temperatures and increased precipitation fostered a mesic forest in northwest Florida dominated by high numbers of oak (comprising 40% of pollen totals), hickory, elm, ash, and hornbeam.  Cypress, sweetgum, sycamore, and myrtle were also common.  Chestnut didn’t range this far south in this part of Florida during Colonial times, but during the Mid-Wisconsinian Interstadial, chestnut pollen was abundant in the air.  The authors of the below referenced paper believe the pollen was from the American chestnut, rather than chinkapin which is a small bush.  The pollen from these 2 related species can’t be distinguished, but the amount suggests it originated from great forests of chestnut, not small understory bushes.  At the beginning of the mid-Wisconsinian Interstadial pine was still common, but pine pollen dropped to less than 20% as the climate warmed.

Pollen graph from the below referenced paper.  Shows the pollen levels from the last 40,000 years.  Click to enlarge.

Between ~31,000-~29,000 a transitional phase occurred.  The climate rapidly began to become colder and drier as the Laurentide Glacier over Canada resumed expansion.  Pine increased in abundance and oak remained common but chestnut, beech, and hornbeam disappeared.  Marsh elder, a plant that thrives in fluctuating water conditions, was common, indicating dramatic dry/wet seasons.

The Last Glacial Maximum, the coldest stage of the most recent Ice Age lasted from ~29,000 BP-~14,000 BP.  Pine pollen increased to over 80%.  Oak, hickory, and cypress were still present but at low levels.  A low diversity and density of plants covered the landscape.  Shallow water plant species macrofossils, such as quillworts and small pondweed, dominate this level of the core, showing lower water levels within Camel Lake.

A sudden change in climate is evident in the part of the core dating to between ~14,000 BP-~12,000 BP.  Pine pollen immediately drops from over 80% to less than 20%.  Hickory increased to an astonishing 25%.  A forest represented by this much hickory has no modern analogue.  Spruce represented 8% of the pollen and was soon joined by beech also representing 8%.  A hickory-spruce-beech forest interspersed by small prairies where grass, ragweed, wormwood, composites, and marsh elder grew composed the landscape.  Scientists initially misinterpeted the results of their study from this time period and proposed that this phase was the coldest of the Ice Age in Florida, colder even than the LGM.  However, this was before the discovery of Critchfield’s spruce, an extinct species of spruce thought to have grown in temperate climates.  Though Camel Lake produced no macrofossils of Critchfield’s spruce, it was probably the species exuding the pollen discovered in the core.  Critchfield’s spruce macrofossils have been found in Louisiana and southwest Georgia (https://markgelbart.wordpress.com/2011/09/03/the-extinction-of-critchfields-spruce-picea-critchfieldii/) .  With this in mind a better interpetation of the data indicates temperatures only slightly cooler than those of today and with increasing atmospheric moisture during this time period.

How did a forest of hickory, beech, and an extinct species of spruce frequented with prairie openings become the dominant type of flora for 2,000 years here?  I propose that megafauna and passenger pigeon foraging suppressed the spread of oaks which normally dominate in this type of climate.  Llamas, deer, peccaries, bison, bears, and passenger pigeons gobbled up the acorns.  But hickory nuts have hard shells, beech can grow from sucker roots, and spruce cones were not as palatable.  These defense mechanisms gave them an advantage over oaks. Increased frequency of thunderstorms spawned lightning-induced wild fires that created the prairie openings.  I regard this time period as harboring a particularly interesting environment in northwest Florida, the likes of which may never be seen again.

From ~12,000 BP-at least ~10,000 BP an increase in oak, sedge, and grass suggests a drier warmer climate.  The climate became so dry between 10,000 BP-7760 BP that no sediment was deposited and there is no pollen record for that time period here.  Since ~7760 BP the modern composition of plants as discussed in the first paragraph of this essay has predominated.  Climate has changed little over the past 7700 years following the final dissolution of the massive glacial Lake Agassiz in Canada…at least in comparison with Ice Age climate fluctuations. (See also https://markgelbart.wordpress.com/2011/01/06/temporal-correlations-between-lake-agassiz-the-okefenokee-swamp-and-ancient-flood-myths/)

Reference:

Watts, W.A.; et. al

“Camel Lake: A 40,000 Year Record of Vegetational and Forest History from Northwest Florida”

Ecology 73 (3) pp. 1056-1066 June 1992