Archive for August, 2010

Pleistocene Passenger Pigeon Populations

August 27, 2010

(Please forgive the excessive alliteration in the title.)

It’s hard to imagine the massive number of passenger pigeons (Ectopistes migratorius) that used to live in North America as recently as the mid to late 19th century.  For a description of their numbers, I’ve dug up an account J.J. Audubon gave in his Ornithological Biography.  Before I reprint this passage I want to comment on his writing style.  I enjoy his prose, but he does have a bad habit of writing in the passive voice, a style Stephen King in his book, On Writing, referred to as farting in an elevator.  Also, English was his second language because he was born in France.  Nevertheless, I think this makes for a fascinating description of a nature scene that no longer exists.

The multitudes of wild pigeons in our woods are astonishing.  Indeed, after having viewed them so often, and under so many circumstances, I even now feel inclined to pause, and assure myself that what I am going to relate is fact.  Yet I have seen it all, and that too in the company of persons, who, like myself, were struck with amazement.

In the autumn of 1813, I left my house at Henderson, on the banks of the Ohio, on my way to Louisville.  In passing over the barrens a few miles beyond Hardensburgh, I observed the pigeons flying from north-east to south-west, in greater numbers than I thought I had ever seen them before, and feeling an inclination to count the flocks that might pass within the reach of my eye in one hour, I dismounted, seated myself on an eminence, and began to mark with my pencil, making a dot for every flock that passed.  In a short time finding the task which I had undertaken impractical, as the birds poured in countless multitudes, I rose, and counting the dots put down, found that 163 had been made in 21 minutes.  I traveled on, and still met more the farther I proceeded.  The air was literally filled with pigeons; the light of the noon-day was obscured as by an eclipse; the dung fell in spots, not unlike melting flakes of snow; and the continuing buzz of wings had a tendency to lull my senses to repose…

“It may not, perhaps, be out of place to attempt an estimate of the number of pigeons contained in one of those mighty flocks, and of the quantity of food consumed by its members.  The inquiry will tend to shew the astonishing bounty of the great Author of Nature in providing for the wants of his creatures.  Let us take a column of one mile in breadth, which is far below average size, and suppose it passing over us without interruption for three hours, at the rate mentioned above as one mile in a minute.  This will give us a parallelogram of 180 miles by 1,  covering 180 square miles.  Allowing two pigeons to the square yard, we have one billion, one hundred and fifteen million, one-hundred and thirty-six thousand pigeons in one flock.  As every pigeon daily consumed fully half a pint of food, the quantity necessary for supplying this vast multitude must be eight million seven hundred twelve thousand bushels per day.”

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Some archaeologists believe the massive population of passenger pigeons that colonists in North America reported from 1700-1870 was a temporary phenomenon.  Thomas Neuman has written at least two journal articles suggesting passenger pigeon populations exploded following the decimation of Indians after their first contact with European diseases such as smallpox, influenza, and measles.  Before this, Dr. Neuman believes this species was not particularly common.  Supposedly, when Indian populations were reduced, there was more forest mast available for birds because humans weren’t gathering the nuts and acorns they fed upon.  In his book 1491 Charles Mann discusses this theory and notes that archaeologists find few passenger pigeon bones at sites of large Indian settlements.

I disagree with this theory because it makes little sense for several reasons which I shall enumerate.

1. Passenger pigeons could not survive as a species unless they existed in extremely large populations.  The survival strategy of this species was to reproduce rapidly and roost and nest in enormous colonies so that they overwhelmed predation.  Predators ate many individuals, but there was a limit to how much their stomachs could hold.  If, as these archaeologists suggest, the passenger pigeon was just an occasional bird, the species would’ve become extinct long before the white man arrived on the continent because their defense mechanisms revolved around living in large colonies.

2. Even if human populations were at the high end of what archaeologists believe, they would’ve made little impact on the amount of forest mast available.  Pre-Columbian forests were extensive, and there was always plenty of forest mast for both humans and huge pigeon colonies.

3. Archaeologists don’t find many passenger pigeon bones in sites of large Indian settlements because Indians probably went to their roosting grounds and feasted on them there and simply didn’t bring the bones back to their villages.

4. Jacques Cartier, an early explorer, reported large pigeon colonies on Prince Edward Island in 1534…before Indian populations were reduced by disease.

5. Pigeon fossils are abundant in an early Holocene fossil site in Western Canada (Charlie Lake, British Columbia).  They are also a common fossil in late Pleistocene avifaunas including Bell Cave, Alabama, Cheek Bend Cave, Tennessee, and Ladds and Kingston Saltpeter Cave in Georgia.

At Ladds fossils of only 4 bird species were discovered.  Passenger pigeons were 1 of the 4.  This may be coincidence, but it’s believed that passenger pigeon biomass made up 25% of all bird populations in North America during the early part of the 19th century.  Many more species of birds were found in the deposit at Kingston Saltpeter Cave.  I compared the minimum number of individual passenger pigeon fossils from KSC to the total bird remains of all other species found there.  Ruffed grouse were the most common species, making up 30% of bird remains, but passenger pigeons made up 6%, despite being a highly migratory bird.  Assuming they spent 6 months of the year around KSC, that means at times, they may have made up to 12% of the bird population in the area.  If they stayed in the area around the cave for only 2 months of the year, they quite possibly made up 36% of the bird population at certain times of the year there.

I must mention, however, that estimating ancient bird populations based on the number of bird fossils found in cave deposits is a rather dubious method.  Nevertheless, habitat for passenger pigeons in southeastern North America during the Pleistocene must have been ideal for this species.

During colonial times this bird nested throughout the midwest, but spent September-February in southeastern states.  For much of the duration of the Wisconsin Ice Age, most of the area where they later nested was under glacial ice, so it’s likely their nesting areas shifted south.  They probably were year round residents everywhere south of the Laurentide ice sheet, except during nesting season when they nested in southern river bottomlands where beech and oak trees remained plentiful, even during cold arid climatic phases.

Today, beech trees are a rare relic in much of the southeast, but during certain climatic phases of the Wisconsin Ice Age, they were even a dominant tree on some lands, according to records of fossil pollen in Alabama, and South Carolina.  From 14,000-11,000 years BP beech was a common tree, while pine, which dominated southern forests during the LGM, temporarily declined drastically.  Beech is well adapted to pigeon and squirrel foraging because this tree spreads through sucker roots, and if animals eat the tree nuts, this species can still propagate.  Beech tree pollen is also present in the Nodoroc fossil site in central Georgia near Winder and at the Gray’s Reef site off Sapelo Island, which was above sea level 30,000 years ago.  The latter site yielded evidence of a forest consisting of a strange mixture of cool temperate and warm weather species of plants.  The south’s Ice Age ecosystem was a mixture of woodlands and grasslands, and it provided excellent habitat for passenger pigeons.  I think the expansion of southern beech tree forests, as the Ice Age waned, is evidence the population of pigeons may have spiked about 14,000 years BP, creating the nucleus that later colonized the midwest after the glacier melted and broadleaf trees re-established themselves there.

References.

Driver, J.C.; and K.A. Hobson

“A 10,500 year sequence of bird remains from the southern boreal forest region of western Canada”

Arctic 45 (2) 1992

Ellsworth, Joshua; and Brenda McComb

“Potential effects of Passenger Pigeon flocks on the structure and composition of pre-settlement forests of eastern North America”

Conservation Biology 17 (6) pp. 1548-1558 2003

Mann, Charles

1491

Knopf 2005

www.paleodb.org

Georgia’s Pleistocene Horses

August 20, 2010

A herd of handsome, reddish-brown horses graze on a small beautiful prairie at the bottom of a lightly forested foothill.  A stallion pauses and raises his head from a clump of grass and white asters, while his harem of six with three foals continue tearing at the tawny and green broomsedge.  He detects the distinct odor of dire wolf nearby.  He whinnies in alarm and begins high-stepping as if signaling for his mates that they must gallop away from this place and now.  The mares get ready to follow his lead, but one seems reluctant to leave.  He nips her on her side to get her going, and they stampede 400 yards to the other side of the prairie where he leads them on a well-used trail through a young stand of oaks and pines.  A flock of grouse explode into the air, startling the horses and sending them in a different direction.  They hurdle bushes, vines, and fallen trees and reach a small creek.  Here they encounter a lone bull mastodon which they perceive as no threat.  They stop and drink, the wolves no longer close enough to pose an immediate threat.

A scene such as I described was probably a common one in North America during the Pleistocene.  Fossils of horses are usually found in most Pleistocene sites.  In Georgia disarticulated horse bones and especially teeth have been recovered from Ladds Mountain and Kingston Saltpeter Cave in Bartow County, and from the Isle of Hope, the Mayfair site, Porter’s Pit, Savannah River Dredgings, and Turtle River Dredgings along the state’s coast.

I perused the scientific literature to determine how many Pleistocene species of horse there were in what’s now Georgia and have concluded there were at least two.  An early paleontologist (Leidy, 18th century) identified one horse fossil from Georgia as belonging to the complex-toothed horse (Equus complicatus), also found in many eastern sites from Kentucky to Mississippi.  Horse fossils from South Carolina have been identified as belonging to the brother horse (Equus fraternus).  And Dr. Clayton Ray wrote that horse teeth from Ladds compared favorably to those of the Mexican horse (Equus conversidens).  However, a genetic study conducted by scientists from the San Diego Zoo compared DNA from the modern horse (Equus caballus) with that from Pleistocene-age fossils of the Yukon horse (Equus lambei), and they determined the two were actually one and the same species.  This calls into question the supposed large number of species of North American horses living here during the Ice Age.  It’s likely the number of species is inflated and many of the supposed different species are also simply no different than the modern horse, so loved by many today.

The confusing classification of Pleistocene horses is no surprise.  Different scientists in different places looked at newly discovered fossil horse teeth and couldn’t find an exact match, so they declared them as belonging to new species when the differences from known teeth were probably interspecific and due to a wide range of natural variance because horses were so abundant and widespread.  Imagine if horses went extinct today, and 10,000 years later a scientist in one region found bones of a large Clydesdale horse, and a scientist in another region found bones of a Shetland pony.  Each would conclude they’d discovered a new species, not realizing the great variability within the species.

True horses, known as caballoids, inhabited Georgia, but wild asses or donkeys, known as hemionids, lived here as well.  In Florida fossils of the pygmy onager (Equus tau) are sometimes found.  The hemionids are also split into many different species but probably can be simplified into one.

Upper left photo is of a wild horse.  Upper right is a photo of a horse tooth identified as Equus complicatus, that was discovered near Natchez, Mississippi.  Bottom photo is of Asian wild asses.  The confusing number of Pleistocene species of horses can probably be simplified into two:  the true horses or caballoids, and the wild asses, or hemionids.  The horse photo is from www.rewilding.org.  The ass photo is from www.birding-southamerica.com. The tooth photo is from an interesting website www.backyardnature.net.  An essay on this latter site discusses the glacial loess found in northern Mississippi.

During the Pliocene the zebra was probably the most common horse species in what’s now Georgia.  The zebra may have been one of the first single-toed horses to  evolve from their 3-toed ancestors.  There’s no way of knowing whether it had stripes like modern zebras.  Photo from www.JamesWarwick.co.uk.

Farther back in time, during the Pliocene, a species of horse (Equus simplicidens) resembling Grevy’s zebra roamed over what’s now Georgia along with the last of the 3-toed gazelle horses which were a dominant herbivore throughout the Miocene.  Horses first evolved in North America, and scientists found evidence of the very oldest known species of horse (the dawn horse) at the Red Hot Fossil Site in Mississippi.  A Wal-Mart has been built next to the site, but the site is still protected.  Fossils from here date all the way back to the Eocene, some 50 million years ago.  The dawn horse is famous for being at the bottom of the horse family tree in biology textbook discussions of horse evolution.

What happened to North America’s horses?

They became extirpated from the continent about 12,000 years ago.  I think human hunting contributed to the destruction of the entire population.  Humans didn’t kill every last individual, but they increased the mortality enough so that combined with normal natural mortality due to disease and predation, it exceeded the horse’s ability to reproduce and maintain a viable population.  Climate change models of extinction for North America’s horses don’t make sense.  When Europeans re-introduced horses, the beasts thrived in feral populations everywhere from Georgia to Nevada.  It’s hard to imagine a climatic phase that occurred 12,000 years ago that for only a narrow window of time rendered the entire continents of both North and South America unfit for horses.  And there is even archaeological evidence of humans hunting North American horses.  Clovis arrowheads with horse blood on them have been discovered associated with horse bones at Wally’s Beach in Alberta, Canada.  The scientists who studied the site think human-hunting combined with climate change caused the extinction of horses on the continent, but I disagree.  It was either one or the other.  I favor human hunting because horses survived millions of years of sometimes drastic climate changes but didn’t become extinct here until man shows up in the archaeological record.

Unlike bison, wild horses don’t migrate long distances.  Once humans exterminated them from a region, they were gone.  The last wild horses and asses lived in only the most remote areas of Asia and north Africa, indicating these regions remained less populated with people than any region in North America.

It pleases me to think of wild horses galloping across the woods and savannahs of Georgia.  Today, a nearby neighbor keeps horses that I sometimes hear whinnying in the evening.  I relax and imagine myself living in a cabin 36,000 years ago.

Atlatl Adventures Part 1

August 13, 2010

Men designed and used deadly advanced weapon systems thousands of years before firearms existed.  Even before the bow and arrow, man’s intelligence provided the solution to the problem of how to subdue much larger, powerful, and faster beasts that were born with fang and claw.  Archaeologists know not when man first developed the spear-thrower, also known as the atlatl, but the earliest evidence of this weapon is from a site in France that dates to 19,000 years BP.  The atlatl allowed man to extirpate or render extinct many large animals that reproduced too slowly to maintain a viable population when faced with an increase in mortality.

The atlatl seems simple but is a marvel of technology, considering what materials primitive men had available.  The atlatl is basically a heavy short stick upon which a long spear is loosely attached.  The stick affords extra leverage, enabling the spear to be thrown a greater distance and with more speed and velocity.

The atlatl is the lower object; the spear or dart is the upper object.  Bob Perkins engineered this atlatl.  It’s a replica of those found in the Great Basin which I believe includes Nevada and parts of California.  The dart is made of aluminum.  The Indians would’ve used a lightweight wood or bamboo.

This is the weight that adds stability to throws.  It’s held on to the atlatl with sinew.

This is the bone hook upon which the dart is loosely attached before a throw.

The handle of the atlatl.  The thrower puts their thumb and middle finger between the straps.

I’m about to throw the spear.  It wasn’t hard to launch competent-looking throws immediately.

After release.  Who cares what the neighbors think?  They already know I’m a weirdo.

Paleo-indians didn’t wear shirts.  Why should I?  It’s 100 degrees.

I found it quite easy to execute good-looking throws as soon as I began, and I’m only of slightly above average athleticism and dexterity.  My throws averaged 30-40 yards which is far shorter than the world record which exceeds 800 feet.  I haven’t had time to purchase a target yet, so after throwing the spear up and down the street, I tried aiming for the newspaper tube from about 25 feet away.  I came close–putting it between the tube and the mailbox a couple times, but most of my throws sailed high.  Possibly, the ideal range for me might be 50 feet.

There is youtube video of a 7 year old boy killing a deer with a spear thrown with the aid of an atlatl, but tough-skinned Pleistocene mammals must have posed a problem.  Even heavy stone arrow heads might’ve bounced off the thick skin, especially that of the edentates such as giant armadilloes and ground sloths.  The paleo-indians must’ve aimed their arrows at vulnerable spots.  And there is evidence of this.  There’s a kill site in Venezuala that suggests the Indians impaled a haplomastodon in the anus.  This kind of wound would cause death through either blood-poisoning or bleeding, and men could track the animal until it died.  In areas of the world where elephants are successfully protected from hunting, they tolerate the approach of humans to a reasonable distance.  On one nature program (I can’t recall which one) a scientist was able to approach Asian elephants within spear-throwing range.  When he got too close, the elephants merely turned their backs and kicked out as a warning.  This behavior offered an easy target for a spear thrown up its buttocks and is evidence of how the kill site in Venezuala transpired.

The atlatl was an effective weapon.  Even after bows and arrows were invented in North America about 3000 years ago, many Indians still used them, and Australian aborigines never had the need to invent them and used atlatls which they called woomeras.  (Atlatl is an Aztec word.  Aztecs used them to kill at least some Spanish conquistadors in their losing war.)

This entry is part 1.  My series on atlatl adventures will be irregular, written after whenever I have a chance to experiment with my new toy.

References:

www.atlatl.com

www.flight-toys.com/atlatl.html

Parallel Unconformities in Florida and South Carolina Fossil Sites

August 9, 2010

Unconformities often puzzle geologists.  An unconformity is a geological term in the study of stratigraphy for a region where sediment from one age overlays sediment from an older age, but fill from the age in between is missing.  For example at the Peace River fossil site located in southwest Florida, late Pleistocene-age fossils are found in sediment over fossiliferous Miocene-age sediment, but rocks and fossils from the Pliocene and early Pleistocene are completely absent.  Geologists are some times at a loss to explain exactly why unconformities occur in certain areas, and of course, creationists jump all over the lack of a definitive answer as proof against an old age earth.  However, they are wrong.  Though scientists don’t know for sure why an unconformity occurs, there are plausible reasons.

Most likely, the Pliocene and early Pleistocene were particularly arid.  The rivers in the region dried up and floods were rare.  Floods wash sediment over bones, thus creating fossils, so without fluvial sedimentation, fossil evidence never was preserved from this intervening age.  This dry climate phase may explain why Georgia’s piedmont is almost barren of Pliocene and Pleistocene fossils, though I’m convinced a concerted search of Georgia’s river basins would discover some of the latter age here.

The fossiliferous strata off the coast of Edisto Beach, South Carolina parallels that of the Peace River fossil site and may be due to the same climate phase.  This site too yields both late Pleistocene fossils mixed with Miocene shark’s teeth, so this unlocated Pleistocene strata must overlay Miocene strata, and the ocean currents are eroding both.  At the Ashley River site, also in South Carolina, the Pleistocene fossils overlay even older Oligocene strata.

In the Peace River the fossils are located in an area of only about 84 square feet in sediment about 6-12 feet underwater.  Scuba divers uncovered the fossils.  Miocene fossils are not only found underneath the Pleistocene ones, but they’re intermixed with them and river currents even work them to modern surfaces.  As river currents wash away ancient sediment, they expose these fossils.  Nevertheless, scientists can use knowledge of chemistry to discern the difference in age between Miocene and Pleistocene fossils.

Scientists analyze the ratio of rare earth elements within the fossils.  Rare earth elements are a family that aren’t particularly rare but consist of few a layman would know.  They include 14 in the lanthanide series and 14 in the actinide series.  All actinides, such as uranium, are radioactive.  Lanthanum, cerium, and erbium are some examples of lanthanides.  Rare earth elements exist in small quantities in ground water, and they occur in consistent ratios with each other.  However, these ratios change over time.  When animals drink water they ingest these elements and absorb them into their bones in the same consistent ratios.  Naturally, Pleistocene fossils have ratios of rare earth elements that occured in Pleistocene ground water, while Miocene fossils have ratios of rare earth elements from Miocene-age water.

The list of Pleistocene fossils found at the Peace River is impressive and includes large, warm climate species.

gar

box turtle,

giant tortoise

river cooter

red bellied turtle

rattlesnake

undetermined duck or goose

cormorant

turkey

pampathere (giant armadillo)

glyptodont

eremotherium (giant ground sloth)

Harlan’s ground sloth

raccoon

Florida spectacled bear

dire wolf

jaguar

bobcat

giant beaver

capybara

tapir

horse

flat-headed peccary

collared peccary

stout-legged llama

long-necked llama

bison (antiquas)

white tail deer

mammoth

mastodon

manatee

Miocene fossils from this site are largely marine–shark’s teeth, ray plate teeth, fish bones, dugong bones, and whale bones.  Notably though, 20 specimens from 5 species of three-toed gazelle horses have been recovered here.  Here’s the list:

Cormohipparion plicatile

Cormohipparion ingenuum

Pseudohipparion skinneri

Calippus elachistus

Nannihippus marganui

Three-toed gazelle horses were a common herbivore of the Miocene.  They had a slender build resembling modern day deer.  During the later Pliocene deer likely began to replace them in the ecological niche they occupied, while surviving horses evolved into the one-toed horses of today.

References:

Hulbert, Richard; Gary Morgan, and Ardreas Kerner

“Collared Peccary (Mammalia, Artiodactyla, Tayassuidae, Pecari) from the late Pleistocene of Florida.”

Museum of Northern Arizona bulletin 65

Whitten, Kenneth; and Kenneth Gailey

General Chemistry with Quantitative Analysis

Saunders College Publishing 1984

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Bob Perkins has shipped me an atlatl.  Future blog entries will include an erratic series entitled “Adventures with an Atlatl.”  I’m also planning on entries about Georgia’s Pleistocene Horses, Pleistocene deer, a study of passenger pigeons, and another erratic series detailing my time travel fantasy of living in Georgia’s Pleistocene before people colonized the region.  This includes what technology I would bring back with me, what kind of house I would build, and what foods would I procure.

Carolina Parakeets, the now extinct Pliocene relic

August 2, 2010

Most species of the avian family (Psittaciformes) that includes parrots, parakeets, and cockatoos are tropical and not well adapted to surviving sub-freezing temperatures.  But a formerly common bird, the Carolina parakeet (Conuropsis carolinensis) did live as far north as the shores of the Great Lakes, until overhunted to extinction–the last survivors dying between 1918-1930.  John Audubon kept a journal of his trip down the Mississippi River in 1820, and he reported large flocks of these colorful birds living in the river bottom swamps.  On one occasion he killed twenty for specimens he could use as models for his portraits.

Portraits of the extinct Carolina parakeet by John Audubon.  He used birds he killed as models for his paintings.

Carolina parakeets nested in colonies , laying eggs in hollow tree cavities.   Like the extinct passenger pigeon, they survived predation by producing more offspring than predators could destroy–a kind of overwhelming fecundity.  They couldn’t survive anthropogenic overhunting, however.  Farmers considered them pests because these seed-eating birds destroyed fruit to get at the kernels, and they swarmed over shocks of harvested wheat to eat the grains.  So the farmers killed as many as they could.  They were quite easy to massacre because of a fatal behavioral flaw.  When a hunter shot into a flock, the noisy birds would scream in alarm, take to the air, circle the area, and alight in the exact same place as the slaughter of a few minutes earlier.  Eventually, the flock would be completely destroyed.

In my book Georgia Before People I wondered why they hadn’t been saved from extinction by pet fanciers.  After reading Audubon’s journals, I can understand why.  Audubon wrote that they made “indifferent” pets.  Actually, from his description, it sounds like they made terrible pets.  They never learned to mimic human voices or pretty bird songs, but instead emitted an annoying loud and constant shriek.  Upon escaping a cage, they used their powerful bills to rip apart furniture, books, etc.

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The Pliocene (5 million-2 million years BP) was a much warmer epoch than the Pleistocene (2 million -11,000 years BP).  Accordingly, a greater diversity of birds existed in North America because they weren’t limited to those species able to survive frigid conditions.  Subsequent Ice Ages reduced the variety of birds on this continent, including most of the Psittaciformes, but Carolina parakeets were the one member of this family that did evolve the ability to live in areas with sub-freezing temperatures.  They were a Pliocene relic, along with such plant species as passion flowers and paw paw trees.  Both of these plant families have large numbers of tropical species, but only one that evolved with the capability of surviving in temperate climates.

During the Pleistocene’s warmer stages, the interstadials and full blown interglacials, Carolina parakeets must have expanded their range almost to the extent that they did during the Pliocene, but curiously I’ve found no reference to their fossils being discovered at any Pleistocene fossil site, though I know they must have lived in North America then.

References:

Audubon, John

Audubon: Writings and Drawings

Penguin 1999