Pleistocene Passenger Pigeon Populations

(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

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Pleistocene Survivors–The Corvids

As I noted in the very first blog entry I wrote for this website, every animal and plant speciess alive today survived and had an ecological niche during the Pleistocene.   Perhaps one of the most remarkable and successful families of Pleistocene survivors are the corvids–a bird family that includes crows, ravens, jays, magpies, and nutcrackers.  Today, only three species of corvids inhabit Georgia regularly.  In addition to those,  ravens may occasionally appear in the mountains of the northern part of the state, but their numbers have drastically declined in the region for reasons I discuss later.  But during the Pleistocene, there were seven species of corvids that lived within what’s now the state boundaries, though not necessarily simultaneously.  Here’s a look at each.

Illustration by Louis Agassiz Fuertes

Northern Raven–Corvus corvax

This is a bird of the deep wilderness.  Because Georgia Before People was nothing but wilderness, they were a common species in the northern half of the state and probably in the southern half too.  They are large–about the size of a small hawk.  I’ve never seen one in the wild but was impressed with the size of a mounted specimen I saw at a nature center in the Nantahala National Forest.  Some large crows fall within the size range of ravens, but there are some other features that can help one discern the difference between the two–ravens have a kind of beard under their chin, a more rounded tail, and a different call.  Though they’re omnivorous, they favor meat more than common crows.  Whereas this species thrived scavenging from the Pleistocene megafauna carrion and later from the herds of bison that once roamed across the Great Plains, they were unable to adapt when man converted grassland to fields of grain, nor did they like forests converted to suburbs, and therefore their range has contracted to remote wilderness areas.  Raven fossils have been recovered from Kingston Saltpeter Cave in Georgia (Bartow County) and Bell Cave in northern Alabama, suggesting they were once even more widespread in the southeast than they were when Columbus discovered America.

Common Crows–Corvus brachyrhyncos

The range of these intelligent, adaptable birds has expanded, while that of the raven has contracted.  They’re more omnivorous than ravens and actually prefer the company of man, thriving on our grain fields and garbage dumps.  They love nesting in suburbs which provide the perfect habitat for them, and they require much smaller nesting territories than ravens.  But they did live during the Pleistocene too.  Genetic tests show they diverged from European carrion crows 2 million years ago, about when they colonized North America.  Specimens of crows are also common in the fossil record.

Fish Crows–Corvus ossifragus

Scientists debate whether this is even a different species than the common crow.  Genetic tests show common crows are ancestral to this one.  They live along waterways, eating fish, shellfish, and sea bird eggs.  They also have a different call than the common crow.

Illustration by Louis Agassiz Fuertes

Blue Jay–Cyanocitta cristata

These common, noisy jays prefer oak forests and suburbs.  Oak forests existed throughout the Pleistocene, though their extent fluctuated with climatic conditions.  Fossils of blue jays were discovered at Kingston Saltpeter Cave, dating to about 13,000 years ago.

Florida Scrub Jay–Aphelocoma coerulescens

This species no longer lives in Georgia, but it must have inhabited this area sometime during the Pleistocene.  Currently, this bird’s range is a discontinous one with a population from Nebraska west to California, and another in central Florida where it inhabits scrubby prairie, alongside the burrowing owl.  During some climatic fluctuation of the Pleistocene, this scrubby habitat was more widespread across the continent, as I discussed in my blog entry entitled, “The Disjunct Range of the Burrowing Owl.”  When the climatic phase favorable to the development of scrubby prairie maximized across the region, scrub jays lived in south Georgia.

Gray Jay or Canada Jay–Perioreus canadensis

This species no longer lives anywhere near Georgia, but during the Pleistocene its current range was under miles of glacial ice, rendering that area uninhabitable.  Today, it lives in Canada and the Rocky Mountains, preferring deep wilderness areas, consisting of coniferous forests, where they’re known as “camp robbers,” because they frequent logging camps and are so tame, being unaccostomed to people, they scavenge human food and miscellaneous items without fear.  During the Ice Age the Laurentide Glacier depressed this species range south.  Fossils of gray jays were discovered in Cheek Bend Cave in Tennessee, and I’m certain this species inhabited north Georgia during the last glacial maximum.

Magpie–Pica pica

Today this species inhabits the far west; its range is nowhere close to Georgia.  It’s a scavenging bird, heavily dependent upon carrion.  Large carcasses of dead megafauna supported populations of magpies in Pleistocene Georgia.  Magpie fossils were discovered in Georgia’s Kingston Saltpeter Cave and in Bell Cave in northern Alabama.

Interesting Facts about Crows

–Besides parrots and macaws, crows and other corvids are the most intelligent birds.  Their skull to body ratio is similar to that of mammals rather than birds.  Their intelligence rivals small monkeys.

–Crows build fake nests to fool predators.

–Experiments prove crows can count to six.

–Crows use tools.  They use splinters to impale insects hidden in crevices.  They drop nuts, clams, and small turtles on hard surfaces.  Some crows even place nuts under rolling car tires.  In experiments they learned to bend wire into hooks which they use to draw small containers of water.

–Crows crush ants and rub them on themselves to ward off parasites.

–Pet crows give their owners names.

–Crows can mimic humans, other animals, and machine noises.  They have dozens of calls, denoting predators, food, and family members.

–Crows living within 3 miles of human beings have a 2.3% annual mortality rate.  Crows living more than 3 miles from people have a 38.9% annual mortality rate.

–Wild crows can live 14-20 years.  Captive crows can live 40-80 years.

–Crows mate for life, but males will cheat.

–Male crows have no penis.  Their sperm is transferred from their cloaca to the female cloaca.  Copulation lasts 15 seconds.

–Crows living in suburban areas require only 10% of the nesting area of crows living in wilderness areas, and they’re more tolerate of range overlap.

–Crows have been reported to eat over 1000 food items, including insects, worms, berries, birds eggs and nestlings, small mammals, bats, fish, snakes, frogs, salamanders, animal dung, grain, nuts, carrion, fried chicken, hamburgers, Chinese food, french fries, and human vomit.

–Crows chase sparrows into buildings, stunning and eating them.

–An experiment showed crows prefer French fries in a McDonalds bag over those in a brown paper bag.

–A nestling can eat 100 grasshoppers in 3 hours.

–Crows sunbathe for Vitamin D.

–Mobbing crows can seriously injure hawks.  Scientists suspect one eagle was even killed by mobbing crows.

–Healthy crows help crippled crows.

–Crows occasionally murder each other for reasons that mystify scientists.

–Crows can learn to distinguish between different people.  On the campus of the University of Washington with 40,000 students and professors, crows learned to specifically avoid the few scientists who had captured them.

Cheek Bend Cave

Northern ravens, magpies, and gray jays weren’t the only northern and western fauna that lived in the southeast during the last Ice Age.  In the late 1970’s scientists excavated Cheek Bend Cave in Tennessee before it was flooded by the Columbia Dam Reservoir.  They found many fossils of species with affinities for cooler climate, including 13-lined ground squirrels, pocket gophers, arctic shrews, water shrews, red-backed voles, yellow cheeked voles, red squirrels, northern flying squirrels, heather voles, wood turtles, hawk owls, boreal owls, saw whet owls, gray jays, pine grosbeaks, prairie chickens, pine siskins, and red-breasted nuthatches.  All of these today are normally found in boreal forests of Canada or western grasslands.  Fossils of some of these species have been recovered from caves in north Georgia as well, providing interesting evidence of cooler climates in the south where a patchwork of open woodland and prairies wilderness existed.  These species lived side by side with those that prefer more temperate conditions.

References

Forbush, Edward

A Natural History of American Birds of eastern and central North America

Houghton Mifflin 1939

Marzluff, John; and Tony Angell

In the Company of Crows and Ravens

Yale University Press 2005

Parmalee, Paul; and Walter Kleppel

“Evidence of Boreal Fauna in Middle Tennessee during the late Pleistocene”

The Auk V. 99 1981