A New Study of Pleistocene Lion (Panthera spelaea) Genetics Confirms it was a Distinct Species

A couple of my readers brought 2 new studies of lion genetics to my attention.  One of the studies confirms the notion that the extinct Eurasian lion (Panthera spelaea) was a distinct species from the present day African lion (Panthera leo).  (See: https://markgelbart.wordpress.com/2012/05/02/three-pleistocene-lions-were-they-distinct-species-or-the-same-animal/ ) The scientists who co-authored this study analyzed the DNA from 2 ~30,000 year old specimens of “cave” lions and used it to compare with the DNA of other felid species.  They extracted the DNA from a lion arm bone found in Yukon, Canada and some lion hair preserved in Siberian permafrost.  The study suggests Panthera spelaea and P. leo were sister species that diverged ~1.89 million years ago.  This divergence precedes the oldest known lion fossil by over 1 million years.  Panthera fossilis, an extinct archaic species of lion, was thought to be ancestral to both P. spelaea and P. leo.  However, this species lived 700,000 years ago, and the divergence likely occurred before P. fossilis evolved.  Fossils of a cat in the panthera genus that date to 3.5 million years ago have been found in Africa, but not enough skeletal evidence exists to narrow it down to species level.  P. spelaea certainly evolved a greater physiological adaptation to colder climates at the beginning of the Pleistocene as periodic Ice Ages became more severe in Eurasia.  This physiological difference may explain the speciation event that separated P. spelaea from P. leo.

Although this study didn’t examine Panthera atrox, the species of lion that occurred across North America south of the Cordilleran Glacier, the results do make it seem more likely that it too was a different species.

Specimens used in the below referenced study–a lion arm bone found in the Yukon and a hair sample found in Siberian permafrost.

The other study looked at the genetics of present day lions living in Africa and India.  This study determined there are 6 distinct regional breeding populations of lions–the west, central, northwest, northeast and south Asian, east/southern, and southwest.  These breeding populations have been repeatedly isolated from each other because of altered landscapes influenced by cyclical Pleistocene climate changes.  Lions prefer open savannah habitats but avoid thick tropical jungles and large deserts.  A belt of monsoons currently brings heavy rain to west central Africa, but this monsoon belt shifts every ~21,000 years, changing the zones of tropical forests and deserts.  Populations of lions become isolated from each other when their favored savannah habitat fragments and is separated by forest and desert.  Other species of savannah habitat show similar intraspecific genetic isolation including giraffe, water buffalo, bushbuck, waterbuck, hartebeest, warthog, cheetah, and spotted hyena.

The common ancestor of all present day clades of African lion diverged ~245,000 years ago.  The genetic evidence suggests all clades of lions were relegated to small refugia during the Last Glacial Maximum when much of Africa hosted landscapes unsuitable for the big cats.  Humans have recently translocated lions from different regions into other regions in an attempt to rebuild populations.  This interference results in the crossbreeding of different clades with each other.  Zoo lions are also crossbred clades for the most part.

References:

Barnett, Ross; et. al.

“Mitogenetics of the Extinct Cave Lion, Panthera spelaea, Resolve its Position Within the Panthera Cats”

Open Quaternary June 2016

Bertoli, L.S.; et. al.

“Philogeographic Pattern in Africa and High Resolution Delineation of Genetic Codes in the Lion (Panthera leo)

Scientific Reports May 2015

 

Salt Domes of Texas and Louisiana

Salt domes are fascinating geological structures of ancient origin.  Over 500 subsurface salt domes have been mapped in Texas, Louisiana, and Mississippi.  During most of the Mesozoic Age from 150 million years BP to 65 million years BP a shallow inland sea covered this region.  The Western Interior Seaway periodically dried, leaving vast salt deposits.  Later, when the ocean re-filled the basin; loads of sediment, sea shells, and coral reefs were deposited on the layers of salt.  Sedimentary rocks such as sandstone, shale, and limestone formed from these deposits.  Meanwhile, organic rich mud buried under these layers was transformed into petroleum.  On the surface of the earth salt is a solid crystal.  But deep underground where it is heated and under high pressure, salt becomes malleable–like toothpaste.  All those miles of sedimentary rock squeeze the salt upward (and sometimes sideways and downward), not unlike an hand squeezing a tube of toothpaste.  This process explains the shape of salt domes.

The top of salt domes comes into contact with ground water.  The chemical reaction of ground water + salt dome creates cap rock, consisting of sulfur, calcite, gypsum, and anhydrite.  Miners extract and process these materials because they have wide industrial and agricultural uses.  The structure of sedimentary rocks on the edge of the salt domes often trap petroleum, so oil wells are drilled adjacent to them as well.

Illustration of subterranean salt domes in Texas.

Illustration of a typical salt dome.  They often trap petroleum deposits.

Cattle grazing on top of Damon Mound, an above ground salt dome located in Texas.

A shallow sea existed over Texas and Louisiana during the Mesozoic.  It repeatedly dried out, concentrating vast amounts of salt.

Although there are hundreds of known subsurface salt domes in the region, just an handful breach the surface.  Damon Mound in Texas (near Houston) is an example of an aboveground salt dome.  It rises 80 feet above the surrounding coastal plain.  Avery Island, Louisiana is another aboveground salt dome.  It is a forested hill, surrounded by salt marsh.  The cap rock here contains Pleistocene-aged sediments where the remains of prehistoric mammals including mammoth, mastodon, Harlan’s ground sloth, Jefferson’s ground sloth, horse, and bison have been excavated.  The Mcilhenny family grows tobasco peppers on Avery Island for their famous hot sauce.  Hugh Mcilhenny, founder of the company, discovered some of these bones after the Civil War.  He kept them on display but the specimens were lost after his death, then later re-discovered by 2 professors.  Some were sent to the Smithsonian Museum and others were sent to LSU and Tulane.  In 2012 they were returned to Avery Island where they are available for display upon request.

The Inner Space Cavern Fossil Site near Georgetown, Texas

Construction workers building an highway bridge over a railroad line accidentally discovered Inner Space Cavern in 1963.  This site is located on the edge of the Edward’s Plateau 1 mile south of Georgetown, Texas.  The eastern side of the Edward’s Plateau is a hilly landscape sitting on Cretaceous-age limestone bedrock.  Rain dissolves limestone creating many underground caves in the region.  The workers drilled down 33 feet and when the drill bit reached the cavern it fell an additional 24 feet becoming lodged in stalagmites.  Inner Space Cavern is also known as Laubach Cave, named after the family who owns the land.  The Laubachs opened up an accessible entrance to the cave, and it is now a tourist attraction.  The cave is underneath the rail line and Highway 35.  Skeletal remains of late Pleistocene age vertebrates have been excavated from 5 sites in the cave.  However, radiocarbon dating of these specimens was executed during the late 1960s and early 1970s when this technology was still in its infancy, and the resulting dates are not considered accurate.  The specimens are at least 13,000 years old, but it’s unclear if they can even be radiometrically dated.

Location of Georgetown, Texas.  Inner Space Caverns is just south of this town.

View inside Inner Space Cavern.

An unique assemblage of grazing fauna roamed central Texas during the late Pleistocene.  Mammoth, bison, horse, camel, glyptodont, and a large extinct species of pronghorn (Tetrameryx shuleri) occupied the plains.  The fossil record suggests Tetrameryx shuleri was restricted to what is now the state of Texas during the late Pleistocene.  Because it was a regional species, it was more vulnerable to extinction when man colonized the area.  A single specimen of the scimitar-toothed cat (Dinobastis serum) was found in Laubach Cave.  Although this species ranged widely over North America, the distribution of its remains suggests the region from Texas and Oklahoma to western Tennessee may have held a core population.  Other large mammal remains found in the cave include Jefferson’s ground sloth, deer (probably white tail rather than mule), flat-headed peccary, jaguar, dire wolf, and the extinct Florida spectacled bear (Tremarctos floridanus).  This is the westernmost known occurrence of the Florida spectacled bear during the late Pleistocene.

Today, the Texas kangaroo rat (Dipodomys elator) is restricted to 10 counties in north Texas bordering Oklahoma.  Remains of this species found in Laubach Cave show it formerly ranged further south.  Black-tailed prairie dogs (Cynomys ludovicianus) and meadow voles (Microtus pennsylvannicus) also no longer occur this far south.  Short-tailed shrews (Blarina carolinensis) don’t live this far west any more.  The presence of these small mammals suggests the climate in this region was wetter with cooler summers during the Ice Age than it is today.

Texas kangaroo rat (Dipodomys elator).  Skeletal remains of this species dating to the late Pleistocene were found in Inner Space Cavern.  It no longer occurs this far southeast.

Skeletal remains of this extinct pronghorn (Tetrameryx shuleri) were found in Inner Space Cavern.  This was its easternmost known occurrence. Note the 4 prongs.

Evidence from Inner Space Caverns shows the extinct Florida spectacled bear (Tremarctos floridanus) lived as far west as central Texas.

The faunal composition of Laubach Cave indicates this region during the Ice Age was dominated by grassy plains but with some riparian woodlands and mesquite/acacia scrubland.  Grazers such as mammoth, horse, and camel clearly are evidence of prairie habitat.  The presence of Jefferson’s ground sloth, deer, cottontail rabbit, spectacled bear, and jaguar (an ambush predator)  make it seem likely that finger shaped communities of trees grew alongside rivers and creeks.  These riparian woodlands probably consisted of centuries old live oaks, cottonwoods, and sycamores.  Flat-headed peccaries, jackrabbits, and kangaroo rats prefer (or in the case of the extinct species, preferred) scrub habitat.  Texas kangaroo rats almost exclusively burrow beneath the roots of mesquite.

Vegetation of this region was similar to that of today, yet slightly different.  The moderate increase in precipitation combined with cooler summer temperatures meant deeper top soils and greater stream flow through rivers.  The alternate climate caused changes in the abundance and density of some species of plants.  Prairies were mixed with some tall grass and some shortgrass, depending upon the topography.  These prairies, like many other natural communities, were thick with wildlife until man came along.

Reference:

Sansom, Jones; and Ernest Lundelius

“Inner Space Cave: Discovery and Geological and Paleontological Investigation”

Austin Geological Society Bulletin 2005

If I could Live During the Pleistocene Part 13–Making Insecticide from Tobacco

This is the newest installment of an irregular series I write for this blog about my favorite fantasy.  I daydream that I traveled back in time to east central Georgia 36,000 years ago where I enjoy a life of self-sufficiency but with modern conveniences. (See: https://markgelbart.wordpress.com/category/if-i-could-live-during-the-pleistocene/ ) In my fantasy world I have a farm surrounded by a high stone fence that keeps mastodons and bears from raiding my garden and orchard, but it recently occurred to me this wall wouldn’t stop insect pests.  As an experiment in my real world yard, I planted peach trees from seed.  Most fruit sold in grocery stores comes from mutated varieties grafted on root stocks because fruit trees don’t produce the same quality from seed, but peaches reportedly are an exception.  Some sources claim peaches grow true to seed, while others say peaches grown from seed are inferior.  My peach trees started to bear this year, and the ones I salvaged tasted as good as farmer’s market peaches.  Unfortunately, most of the peaches fell off or were ruined because of an insect pest known as plum curculio (Conatrachelus nenophar), a little beetle in the true weevil family.  This experience made me realize I needed to revise my fantasy and make my own insecticide, if I want to have fruit at my Pleistocene homestead.  In the modern world I can buy the most delicious local peaches, nectarines, and plums; but I won’t have any fruit in the Pleistocene without spraying.

This is one of my least damaged peaches.  Most of the others fell off long before they ripened.  In some localities spraying fruit is necessary.

I won’t spray until after the petals fall off because I don’t want to poison the butterflies and bees that pollinate the flowers.

Plum curculio.  This species of beetle destroyed all of my peaches.  It is abundant in my neighborhood probably because of the presence of wild plums and cherries.

Plum curculios are common in areas with wild plum and wild cherry trees.  They readily adapted to fruits introduced by Europeans, especially peaches.  The adult females burrow into unripe fruit and make a crescent shaped hole where eggs are deposited.  The crescent shape keeps the larva from being crushed when the fruit grows.  Most fruit falls off the tree, and any fruit that ripens is blemished so badly it can’t be sold.  The trees must be sprayed as soon as the flower petals fall and again when the fruit is in the shuck stage.

 

 

 

 

 

 

 

Tobacco plants.

It is easy to make insecticide from tobacco (Nicotiana tabacum).  Tobacco is in the nightshade family, a group of plants that evolved the ability to produce toxins in their leaves.  These poisons prevent insects and other animals from consuming the leaves.  To make insecticide mix 1 cup of dried tobacco leaves with 1 gallon of water and let it sit in the sun for 24 hours.  Then add 3 tablespoons of liquid soap.  (Just think: people who smoke cigarettes are smoking insecticide.)  The nicotine in tobacco destroys an insect’s nervous system.

I’d have to grow tobacco in my Pleistocene world, but I wouldn’t smoke it.  I prefer marijuana.

 

The Nature of Trials of the Earth by Mary Hamilton

One of the last great stands of wilderness in eastern North America existed along the Mississippi River during the late 19th century.  Loggers ruined this environment between 1880-1910, but in Mary Hamilton’s autobiography, Trials of the Earth, she described the awesome nature of this region.  Though her book focuses on her personal life and all the tragedies and hardships her family endured, I collected all of the interesting tidbits of natural history that she wrote about.

A fascinating book about the pioneer life of a woman in Mississippi and Arkansas during the turn of the 19th century.

In 1896 Mary Hamilton, along with her 2 young children and her brother and sister, followed her husband to a logging camp on Concordia Island, Mississippi.  The island was bound by a chute of the Mississippi River and the main channel.  Her husband was a supervisor at the camp, and he was too busy to bring her himself.  Instead, he marked a wagon trail through the wilderness, and a guide (actually an inexperienced teenaged boy) helped her find the camp where she eventually worked as a cook for 30 lumberjacks.  She was accustomed to this work, having boarded over 100 lumberjacks at a previous camp.

The family settled in a big white tent.  The island consisted of a dense forest of large mature oak, sweetgum, hackberry, and tulip trees with a thick undergrowth of bamboo cane that grew all the way to the lower limbs of the tall trees.  (See: https://markgelbart.wordpress.com/2013/01/28/canebrakes-are-forlorn-landscapes/)  Closer to the river, the forest thinned out, probably because of frequent flooding, and enormous sycamores and cottonwoods grew here.

The lumberjacks felled the trees and lashed them together in rafts to be tugged down the river to sawmills.  Some species of trees float, while others sink, so the lumberjacks had to lash “floaters” with “sinkers.”  Sweetgum and oak sink and had to be lashed to cottonwood, ash, or cypress.

Some species of trees sink, while others float.  Lumberjacks had to lash logs from “floaters” with logs from “sinkers” when they sent them downstream to the mills.

This is how people with wagons crossed rivers before bridges were built.  People who owned the ferry charged for its usage.

Mary’s younger brother was an accident prone Gomer Pyle type, and her husband was afraid he would hurt himself or somebody else, if they put him to work as a lumberjack.  Therefore, they assigned him the task of hunting and fishing to supplement their supplies.  It was difficult to supply this camp with food.  During times of high water, wagons couldn’t reach the camp, and supply wagons occasionally got lost in the wilderness and never arrived.  Sometimes the man in charge of the supply wagon ignored the grocery list and bought candy and cakes instead of the staples they needed.  So hunting was useful.  Deer and black squirrels were abundant.  Apparently, the black phase of the fox squirrel (Scirius niger) was the only species of squirrel on this island.  This surprises me because gray squirrels (Scirius carolinensis) prefer the kind of dense forest Mary describes.  In the south fox squirrels generally prefer more open woodlands.

Black phase of the fox squirrel.

One day Mary’s brother encountered a mother bear playing with her cubs.  He threw down his gun and ran for his life, yelling “there’s a dozen lions after me.”  Bears were plentiful on the island, and the lumberjacks’ diet here included bruin along with local beef and pork (wild hogs ran wild everywhere) and corned beef from New Orleans.  Animals took advantage of the lumber camp as a source of food as well.  A bear stole a quarter of a beef left to hang outside one night.  Raccoons, opossums, and bobcats fought over the camp garbage every night, and Mary heard panthers screaming and wolves howling nightly.  Later, when her family moved to an homestead on the nearby Sunflower River she insisted her husband shine the lantern on her when she went outside to bring in the laundry every night  because she heard a panther screaming regularly on both sides of the river.  People didn’t know much about panthers and wolves then and were very afraid of them. Mary didn’t consider all nature unpleasant.  She liked to hear the birds and frogs in the spring, and one day she collected 5 gallons of blackberries the size of Guinea hen eggs.  The rich delta soil produced berries larger than modern cultivated ones sold in farmer’s markets.

Mary’s husband built a “freshwater shrimp” trap for her brother.  The trap worked and captured bags of “shrimp” everyday, but her brother didn’t know “shrimp” meant crawfish.  He always threw away the crawfish until he was informed of his ignorance.

The Mississippi River shifted direction during their time on Concordia Island.  This caused a near disaster.  The river started eroding the bank overhanging all the rafts of lumber.  The rafts could have become covered in sediment and lost.  They immediately sent for tugboats that hauled the floating rafts and most of the logs were saved.  This event, referred to as “sloughing,” must have been an impressive sight.  Trees fell into the river, and the sediment collapsing made a “boom, boom” sound.

Next, Mary’s family moved to a lumber camp near the Sunflower River, a tributary of the Yazoo.  This region too was all canebrake and woods where panthers screamed and wolves howled every night.  Getting water at this camp was laborious and difficult.  Iron pipes were driven into the ground to reach well water, but oftentimes this was hard water high in magnesium and calcium.  Hard water is safe for drinking but can’t be used for washing dishes or clothes.  Mary softened the water by adding lye made from wood ashes.  The addition of a base binds the calcium and magnesium ions, making the water usable for cleaning.  Too much water became a bigger problem at this camp.  Rainy weather flooded all the surrounding bayous, isolating the camp from civilization, and they ran short of food.  They realized the rising water was going to completely inundate the camp and the wooden clapboard house where they were living.  So Mary’s husband cut a path through a canebrake that led to an Indian mound located above the floodplain, and he built a small boat.  The boat wasn’t big enough for all of them, and he had to make 2 trips to save his wife and 3 children.  Mary waited with her 5 year old daughter and infant son for 6 hours, while her husband carried their other small child to safety and returned.  She spent all this time standing on a chair on the highest ground, holding her baby and comforting her young daughter.  The baby slept the entire time, despite the rain.  She saw a bear, deer, rabbits, mice, and snakes swimming by them, looking for high ground.

Tornadoes often storm up the Mississippi River valley, then turn inland and smash through forest.  Mary describes one such area that was known as “the cyclone,” an area estimated to be at least 36 square miles.  “The cyclone,” located near the present day site of the Parchman State Penitentiary, was an eerie landscape without a single standing tree.  Instead, the ground was littered with fallen timber covered in grapevines, poison oak, and thorny brier bushes.  Ecologists call these environments windthrows.  This windthrow was on rich soil and hosted luxuriant tangles of vegetation, making the area impassable.  Mary tells the story of a well-liked Jewish paymaster who chose to take a shortcut through “the cyclone” rather than travel the 5 mile path around it.  He was bringing the pay to a neighboring lumber camp.  He got lost for 4 days and went half-mad from panic and dehydration.  The thorns tore all his clothing off as he scrambled through the briers.  Search parties failed to find him.  He finally wandered close to the camp, completely naked and incoherent but with the money in his hand.

Mary Hamilton described an area near the present day site of Parchman Penitentiary as “the cyclone.”  It was a windthrow of at least 36 square miles covered in an impenetrable stand of vines, briers, and cane.

Mary worked hard most of her life, but shortly after she married she did enjoy a bit of a vacation in Missouri where she stayed with friends by the Castor River.  Here, she learned how to fish.  She mostly caught bass, but on one early morning before anyone else was awake she caught an eel.  This sent her screaming in terror back to the house.  She was so scared she didn’t let go of the rod and carried the eel to the front door.  Mary wanted to get rid of it, but her husband was from England where eel is considered a delicacy, and he prepared it for supper.  One kind of fish that Mary caught here was referred to as a “white salmon.”  It took a little research, but I determined her “white salmon” was actually a walleye (Sender vitreus).  The old Ozark term for walleye is “jack salmon.” 

Mary caught bass, an eel, and walleye (which she called “white salmon”) in the Castor River.

I’d like to live in a wilderness where panthers scream and wolves howl every night.  And it would be rewarding to live off the land, gardening and raising animals for food.  But I wouldn’t want to do this without modern conveniences.  Mary worked from dawn to past dusk for most of her life.  I envy the wilderness she got to see but not the hard life she endured.

 

 

Pleistocene Roadrunners (Geococcyx californianus)

Roadrunners are neotropical invaders that spread across North America, probably no earlier than the late Pleistocene.  Fossil remains of roadrunners dating to this time period have been excavated from sites in Arizona, New Mexico, and California.  Roadrunners are ground foraging birds in the cuckoo (Cuculidae) family.  All other members of this family prefer the tree canopy.  There are just 2 species of roadrunner–Geococcyx californianus ranges from central Mexico west to California and east to Arkansas and Louisiana and G. velox occurs in tropical deciduous forests from southern Mexico to Nicaragua.  The ancestor of these species likely diverged during an arid climate cycle of the Pleistocene.  G. californianus evolved a preference for desert scrub and cactus environments and moved north across the Rio Grande.  I think they are a fairly recent colonizer of this region because desert grassland and scrub habitat was widespread across southeastern North America during the late Pliocene/early Pleistocene about 2 million years ago, yet there is no fossil evidence of roadrunners in this region from that time period.    If roadrunners lived in southwestern North America during this early time period when their ideal habitat was so widespread, I believe they would have colonized the southeast.  And they would still persist in some areas of the southeast where favorable habitat exists.  There’s no shortage of thickets mixed with clearings in the southeast.  In Arkansas, the easternmost part of their modern range, roadrunners occur in farms and clearings, cedar glades, scrubby woods, and rocky outcroppings.  Currently, the Mississippi river appears to be a barrier that prevents them from expanding their range east.  They haven’t crossed the river yet because they are weak flyers and prefer to run in zigzag patterns between thickets.  They are the fastest runners among birds capable of flight, reaching speeds of 25 mph–about the speed of an Olympic male sprinter.

 

 

 

 

 

 

 

 

Roadrunner killing snake.  They kill their prey by bashing it against the ground until it is senseless.

Roadrunner range map.  I believe the Mississippi River is the barrier that keeps them from expanding their range east.

Video of a roadrunner ambushing an hummingbird at a feeder.

Real life roadrunners are smart like their cartoon imitation.

Pleistocene roadrunners were slightly larger than modern roadrunners but are considered to be the same species.  Scientists believe they grew to a larger size due to cooler Ice Age summers.  The modern smaller birds have more endurance in warmer conditions than larger birds and can chase down their favored prey (lizards, snakes, mice, scorpions, insects, and other birds) for longer periods.

Roadrunners are poorly studied.  I searched The Auk and The Condor, 2 ornithology journals, for more information about them and found very few articles..  They are an intelligent bird, not unlike their cartoon counterpart, and this makes them hard to study because they are smart enough to avoid traps.  This is 1 case when the cartoon imitation of an animal matches its real personality.

 

Passenger Pigeons (Ectopistes migratorius) and Forest Succession

The former abundance of the now extinct passenger pigeon amazed all of the pioneers who witnessed their migration and roosts.  Some researchers estimate passenger pigeons composed 25% of the total bird population in eastern North America during colonial times.  Their migrations consisted of billions of birds that could eclipse the sun for as long as 14 hours.  Pigeon dung fell like “snowflakes” underneath this eclipse.  They nested in enormous colonies, covering many square miles.  Their survival strategy was predator satiation.  With synchronized hatching there were billions of squabs on the forest floor during the week they left the nest and were learning how to fly.  There were just too many for predators to eat all at once. They nested and reproduced in the great deciduous and coniferous forests of the Midwest, then migrated to the middle south during the winter where they still roosted in large colonies.  Passenger pigeon roosts destroyed vast areas of the forest.  The weight of all those birds broke limbs off trees and even busted thick tree trunks in half.  The armies of pigeons vacuumed all the acorns, beechnuts, and chestnuts off the forest floor, leaving no mast for other animals.  But their dung was the most detrimental element of their roosts–overfertilizing the soil and killing all the trees in the vicinity.  Yet, ecologists believe passenger pigeons played a critical role in creating habitat diversity across the landscape.

Illustration showing how passenger pigeons created more diverse habitats.

Flocks of migrating passenger pigeons could eclipse the sun for as long as 14 hours.  Areas of the forest where they roosted were devastated.

Stuffed specimen of a male passenger pigeon.

The response of the environment following the aftermath of a cataclysmic pigeon occupation would have been interesting to study.  Unfortunately, passenger pigeons were overhunted to extinction before scientific studies of their ecological impact could be conducted.  However, we can safely assume the environment recovered in stages.  First, plants; such as ginseng, pokeberry, and Virginia creeper; that thrive in soils rich in nitrogen were the initial species to grow in the open conditions strewn with fallen dead trees and limbs.  Second, as rain reduced the concentration of nitrogen in the soil over the years; ragweed, grasses, sedges, and composites returned.  A shrubby stage with pioneer trees including cedar and pine gradually replaced the grassy stage.  Acorns carried by jays and squirrels sprouted into oaks that grew with the pioneer trees before eventually outcompeting them.  If undisturbed for centuries, shade tolerant species such as maple and beech took over from the oaks. The dead wood from the original pigeon roosts was flammable during dry weather, and wild fires were likely more common, explaining why fire-tolerant species of oaks (burr, white, and black) predominated in the Midwest.

In many areas of the Midwest some species of oaks are in decline, especially white oak, while red oak is increasing.  White oak germinates during the fall when passenger pigeons were absent in this region.  But the pigeons were able to consume spring-germinating red oak acorns after the snow melted.  Moreover, red oaks are less fire tolerant than white oaks.  Oaks are also shade-intolerant and are being replaced by shade tolerant maples.  Ecologists think white oaks are missing the passenger pigeon invasions that created the natural disturbance they need and reduced the competition they now face from red oaks.

Scientists with the Revive and Restore Project hope to genetically engineer the passenger pigeon by cutting and pasting their genes into the embryos of their closest living relative, the band-tailed pigeon.  I doubt they will successfully be able to re-establish passenger pigeons in the wild.  Passenger pigeons fail to breed unless they live in enormous colonies.  To survive predation, they must exist in large numbers…the sheer size of their population was the survival mechanism they required.  Researchers would need to release at least 10,000 birds to establish a successful breeding population in the wild.  Passenger pigeons evolved their survival strategy millions of years ago.  Though 1 genetic study suggests their overall numbers fluctuated with changes in climate phases, I am convinced they always occurred in large colonies. The task of re-establishing these numbers is probably an impossible one.

See also: https://markgelbart.wordpress.com/2010/08/27/pleistocene-passenger-pigeon-populations/