Passenger pigeon

• 1. Introduction

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  In 1813, the naturalist and artist John James Audubon tried to count passenger pigeons with a pencil. He sat on a rise of ground and put down one dot for every flock that passed. In twenty-one minutes he had made 163 dots, and the birds were still pouring in. He gave up the count and rode on toward Louisville, fifty-five miles from Hardensburgh. The flocks kept coming for three days in a row. Audubon wrote that "the light of noon-day was obscured as by an eclipse."

  Today no passenger pigeons remain. How does a bird that dims the midday sun for days on end vanish completely? What did such multitudes eat, where did they nest, and what did the land lose when they were gone? The answers begin with a name that took almost two centuries to settle.

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• 2. Names and Kin

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  In 1758, the Swedish naturalist Carl Linnaeus used a single name, Columba macroura, for two different birds. The passenger pigeon and the mourning dove both sat under it, and Linnaeus appears to have thought them identical. Nothing suggests he ever handled either bird. He built his entry from two older books. One was Mark Catesby's Natural History of Carolina, Florida and the Bahama Islands, published between 1731 and 1743. Catesby called the pigeon Palumbus migratorius and included the earliest published illustration of it. The other source was George Edwards, who described the mourning dove in 1743.

  By 1766, Linnaeus had dropped macroura. He now called the passenger pigeon Columba migratoria and the mourning dove C. carolinensis. That edition also listed C. canadensis, taken from a 1760 description by Mathurin Jacques Brisson. Brisson's bird later proved to be a female passenger pigeon. In 1827, William Swainson placed the species in its own new genus, Ectopistes, partly because of its long wings and wedge-shaped tail.

  In 1906, Outram Bangs pointed out that Linnaeus had wholly copied Catesby's text, so macroura belonged to the passenger pigeon. In 1918, Harry C. Oberholser argued that canadensis should win because it appeared on an earlier page. In 1952, Francis Hemming asked the International Commission on Zoological Nomenclature to give macroura to the mourning dove and migratorius to the passenger pigeon. The commission agreed and made it official in 1955, using its plenary powers.

  The genus name Ectopistes means moving about or wandering, and migratorius points to migration. The full name therefore translates as migratory wanderer. The English name comes from the French word passager, meaning to pass by in a fleeting way. While the bird lived, people used passenger pigeon and wild pigeon interchangeably. Rarer names included blue pigeon, merne rouck pigeon, wandering long-tailed dove, and wood pigeon. In eighteenth-century New France it was the tourte, while French speakers in Europe said tourtre.

  The Lenape called the bird amimi, the Ojibwe said omiimii, and the Kaskaskia Illinois said mimia. The Mohawk word was ori'te. The Choctaw name putchee nashoba means lost dove. The Seneca word jahgowa means big bread, because the bird fed their communities. Chief Simon Pokagon of the Potawatomi reported the name O-me-me-wog. He said Europeans took up none of these names, since the birds reminded them of domestic pigeons. They called the pigeons wild, just as they called native peoples wild men.

  The oldest known fossil of the genus is a single upper-arm bone, catalogued as USNM 430960, from the Lee Creek Mine in North Carolina. It comes from Pliocene rock between 5.3 and 3.6 million years old. For a long time, the mourning dove looked like the obvious cousin. Some authors, including Thomas Mayo Brewer, even filed the mourning dove under Ectopistes as E. carolinensis.

  Genetics overturned that idea. In 2002, Beth Shapiro and colleagues ran the first ancient DNA analysis on passenger pigeon museum specimens, in a paper mostly about the dodo. It placed the pigeon beside the cuckoo-dove genus Macropygia. A fuller 2010 study instead tied it to the New World Patagioenas pigeons, including the band-tailed pigeon of western North America. Its authors suggested the ancestors reached the Americas from Southeast Asia, either over the Pacific or across Beringia. A 2012 study read the nuclear DNA, confirmed the Patagioenas link, and floated the opposite idea that the family began in the tropical New World.

  Museum skins have since become test material for better ways of assembling genomes from degraded DNA. Researchers often sample the toe pads, which can be cut without seriously harming a valuable specimen. No subspecies of the passenger pigeon is known. In the aviary of Charles Otis Whitman, who owned many of the last captive birds, a passenger pigeon once hybridized with a Barbary dove. The offspring were infertile.

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• 3. Feathers and Voice

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  A male passenger pigeon measured 390 to 410 millimeters in length, and the species weighed between 260 and 340 grams. His head, nape, and hindneck were bluish gray. On the sides of his neck sat iridescent display feathers that observers called bright bronze, violet, or golden-green, depending on the angle of the light. His breast was a rich pinkish-rufous that faded to white toward the belly. His bill was black, his legs a bright coral red, and his eye had a carmine-red iris. The white outer edges of his tail carried dark spots that showed clearly in flight.

  The female was slightly smaller and duller. Her forehead, crown, and nape were grayish brown, her breast was buff-gray, and her neck feathers shone less. Her legs were a paler red and her iris an orange red. Young birds resembled females but had no iridescence at all. Pale fringes on their wing feathers gave them a scaled look, and the plumage of the sexes stayed similar through the first year.

  Of the hundreds of surviving skins, only one looks truly abnormal in color. She is an adult female from the collection of Walter Rothschild, now at the Natural History Museum at Tring. Her back and tail are washed brown where they should be gray, and her primaries and underparts are white. Her iridescence is untouched. The brown comes from a shortage of the pigment eumelanin, while the white feathers are thought to be bleaching from sunlight.

  In 1914, Robert W. Shufeldt examined a male skeleton and found little to set it apart from other pigeons. Julian P. Hume looked again in 2015, in more detail, and found several distinctive features. The breast muscles that power the wings were particularly large. The sternum was very large, with a keel 25 millimeters deep. The coracoid, a shoulder bone, measured 33.4 millimeters and was sturdier than in other pigeons. The wings were long and pointed and the tail wedge-shaped. The head and neck were small, so the whole bird looked like a streamlined rock dove.

  A flock's noise was described as deafening and audible for miles. A single bird's voice was loud, harsh, and unmusical. In 1911, the behavioral scientist Wallace Craig published an account of the gestures and sounds, with musical notations, based on watching captive birds in 1903. He wanted to help people recognize any survivors in the wild, since mourning doves could easily be mistaken for passenger pigeons.

  Craig recorded a harsh single "keck" used to catch another pigeon's attention. A scolding "kee-kee-kee-kee" or a repeated "tete" called to a mate or warned off enemies. A long, drawn-out "tweet" could bring a passing flock down into a nearby tree. A soft "keeho" was kept for a mate. A nesting bird gave a stream of at least eight mixed high and low notes that ended in "keeho." Females were quieter and called less often. Craig thought the strident voice and "degenerated" musicality came from life in crowded colonies, where only the loudest sounds carried. He expected this "meager information" to be nearly all that would ever be left.

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• 4. Flocks and Range

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  East of the Rocky Mountains, from the Great Plains to the Atlantic coast, the passenger pigeon lived in the eastern deciduous forests. The main breeding grounds lay in southern Ontario and the Great Lakes states, then south through the states north of the Appalachian Mountains. Winter drew the birds from Arkansas, Tennessee, and North Carolina south to Texas, the Gulf Coast, and northern Florida. They preferred big swamps, especially alder swamps, and settled for pine forest when swamps were scarce. The western forests looked similar, but band-tailed pigeons held them, and competition may have kept the passenger pigeon out.

  Stragglers turned up in several western states, Bermuda, Cuba, and Mexico, often in harsh winters. Records from Scotland, Ireland, and France may be escaped captives or mistakes. More than 130 fossils from 25 US states, including the La Brea Tar Pits of California, show that the range once reached western states. Some of these fossils are 100,000 years old.

  In 1866, a flock over southern Ontario was described as 1.5 kilometers wide and 500 kilometers long. It took fourteen hours to pass and held more than 3.5 billion birds. That figure may represent a large share of the whole species at the time, or even all of it. Henry David Thoreau, by contrast, noted in Concord, Massachusetts, in November 1859 that a modest flock had bred there the previous summer. Flock size swung enormously from place to place.

  At its height the species is estimated at three to five billion birds, which may have made it the most numerous bird on Earth. The researcher Arlie W. Schorger believed it made up 25 to 40 percent of all land birds in the United States. That roughly matches the number of birds that spend each winter in the United States in the early twenty-first century. The writer Christopher Cokinos has suggested that, flying in single file, they would have circled the Earth 22 times.

  At roughly 100 kilometers per hour, the migrating pigeon was a fast and agile flyer. It flapped in quick, repeated beats and moved as nimbly through a forest as across open ground. Flocks flew as low as one meter above the ground in windy weather and as high as 400 meters. They traveled in narrow, twisting columns that observers likened to nearly every conceivable shape. Each bird followed the one ahead, so a whole flock swerved together to dodge a predator. Audubon compared a flock pressed by a hawk to "the coils of a gigantic serpent." On the ground, by contrast, the bird was awkward and moved in jerky, alert steps.

  Roosting areas ranged from a few acres to 260 square kilometers or more. Some were reused for years and others only once. The birds piled onto each other's backs, and thick branches snapped under the load. They slept in a slumped position, with the bill tucked into the breast feathers and the tail held at a 45-degree angle. Droppings could build up to more than 0.3 meters deep. Cold killed many each spring, when birds migrated north too early and froze.

  In 2014, a genetic study of three individuals suggested wild swings in population over the last million years, tied to the ups and downs of the nut supply. It proposed that the bird mostly persisted at roughly one ten-thousandth of its nineteenth-century total, with vast outbreak phases in between. A 2017 study sequenced two more genomes and analyzed the mitochondrial DNA of 41 individuals. It found a stable population for at least 20,000 years, with an effective size of 13 million birds. That is only about one three-hundredth of the historic figure.

  The 2017 study found another surprise. Genetic diversity was very low despite the enormous numbers, and the authors blamed natural selection acting on a huge, cohesive population. They concluded that the earlier suggestion of population instability contributing to extinction was invalid. The evolutionary biologist A. Townsend Peterson said the idea of extreme fluctuations was "deeply entrenched." He added that the study's in-depth analysis and massive data persuaded him.

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• 5. Mast and Forests

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  A crop that swelled to the size of an orange let the passenger pigeon grab food fast. It could reportedly hold at least 17 acorns or 28 beechnuts, plus 11 grains of corn and 100 maple seeds. A very elastic mouth and throat and a joint in the lower bill let the bird swallow acorns whole. A pigeon needed about 61 cubic centimeters of food a day. When a hunter shot one with a full crop of nuts, it hit the ground with a sound like marbles rattling in a bag. Overnight, a muscular gizzard, often holding gravel, ground the food down.

  Beeches and oaks produced the mast, which is the crop of nuts and acorns that forest trees drop. In fall, winter, and spring, the pigeon ate mainly beechnuts, acorns, and chestnuts. Summer brought blueberries, grapes, cherries, mulberries, pokeberries, and bunchberry. It also ate worms, caterpillars, and snails, especially while breeding. It raided buckwheat fields and craved salt, which it found in brackish springs and salty soil.

  Flocks of tens or hundreds of thousands foraged together, overturning leaves, dirt, and snow with their bills. One observer described the motion as rolling, because birds at the back kept flying over the others to the front. The wide leading edge scanned for food. A bird that strayed from the flock hurried back. Each day the birds flew 100 to 130 kilometers from the roost to feed, and some went as far as 160 kilometers. Mast is plentiful in different places at different times and rarely in consecutive years. That is one reason the flocks never stayed put.

  A pigeon could eat and digest 100 grams of acorns a day. Across a population of three billion, that adds up to 210,000,000 liters of food daily. Such appetite shaped the forest. A 2018 study found that the bird's gape limited the seeds it could swallow. Between 13 and 69 percent of red oak seeds were too large, while all white oak seeds fit. Seeds were destroyed in digestion, so the pigeons probably spread them only by regurgitating them or by dying.

  Red oaks drop acorns in spring, when pigeons were nesting and hungry. White oaks drop theirs in fall, when fewer pigeons were around, and they follow an irregular masting pattern. The 2018 study concluded that these habits evolved under pigeon pressure, which helps explain why white oaks dominated where the birds were common. Roosts left behind so much waste that few plants grew there for years. Broken limbs and dead foliage fed fires that favored fire-tolerant bur, black, and white oaks over red oaks. Some ecologists call the passenger pigeon a keystone species, and forest managers have proposed opening canopies to mimic its effects.

  Around 1905, an imported Asian fungus called chestnut blight began to kill American chestnuts, which had supplied much of the pigeon's mast. As many as thirty billion trees are thought to have died in the following decades. The pigeon was already gone from the wild by then. In its absence, white-footed mouse numbers grew exponentially on the leftover oak, beech, and chestnut seeds. Because those mice are reservoir hosts of Borrelia burgdorferi, it has been speculated that the extinction raised the rate of tick-borne Lyme disease.

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• 6. Cities of Nests

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  The largest nesting area ever recorded lay in central Wisconsin in 1871. It reportedly covered 2,200 square kilometers and held about 136,000,000 birds. Colonies like this were called cities. They ranged from 49 hectares to thousands of hectares and were often long, narrow, and L-shaped. Most accounts describe millions of birds. The pigeons showed no loyalty to a site and usually nested somewhere new each year. They reached southern latitudes around March, though a colony might not form until late March, April, or May.

  Courtship happened on a branch, unlike in other pigeons. The male gave a "keck" call, flapped his wings vigorously, and pressed against the female with his head held high. If she was receptive, she pressed back. The pair preened each other and then clasped bills. Audubon wrote that the birds also passed food between their bills. After watching captives, Wallace Craig thought it likely that no food passed and that Audubon had partly relied on analogy and imagination.

  Nests rose within two to four days of pair formation, and a whole colony worked in sync. The female chose the site by sitting on it and flicking her wings. The male then picked twigs and handed them to her over his back while she built the nest beneath herself. A nest used 70 to 110 twigs woven into a loose, shallow bowl through which the egg could be seen. Nests were about 150 millimeters wide. They sat anywhere from 2 to 20 meters up, though typically above 4 meters. One hemlock held 317 nests, and many trees had more than 50. The ground below looked swept clean of twigs but lay buried in dung.

  The pair laid a single white egg, about 40 by 34 millimeters, though two were reported from some nests. Sometimes a second female added her egg to another's nest. A lost egg could be replaced within a week, and one whole colony re-nested after a snowstorm drove it out. Both parents incubated the egg for 12 to 14 days, the male from midmorning to midafternoon. The squab hatched blind, with sparse yellow down. It fed on crop milk, a curd-like substance from the parents' crops, and was given adult food after three to six days. Within 14 days it weighed as much as an adult.

  After 13 to 15 days, the parents fed the young bird one last time and left the nesting area en masse. The squab begged for a day or two, then fluttered to the ground. It was another three or four days before it could fly. The entire cycle took about 30 days. Young pigeons matured in their first year and bred the following spring.

  The louse Columbicola extinctus was long thought to live only on passenger pigeons and to have died out with them. In 1999 it was rediscovered on band-tailed pigeons. Another louse, Campanulotes defectus, turned out to come from a contaminated specimen. There is no record of a wild passenger pigeon dying of disease or parasites.

  Minks, weasels, martens, and raccoons raided eggs and nestlings. Owls, hawks, and eagles took nestlings and adults, while wolves, foxes, bobcats, bears, and cougars took injured adults and fallen young. Cooper's hawk was known as the "great pigeon hawk" because of its success. Yet the sheer size of the flock protected individuals, and so many fat juveniles hit the ground at once that predators could take only a few. This predator satiation may explain the bird's extreme sociability. If left undisturbed, a colony was estimated to succeed 90 percent of the time.

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• 7. Lives Beside Humans

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  For fifteen thousand years or more before Europeans arrived, passenger pigeons and Native Americans shared the eastern forests. A study published in 2008 found that Native land-use practices shaped forest composition through most of the Holocene. Controlled burns, girdling of unwanted trees, and planting of favored ones boosted species that bore nuts, acorns, and fruit. Burning away litter also made fallen food easier to find. Some argue this helped the pigeons, while others say hunting and competition for acorns held them back.

  A 2016 study of ancient DNA found that the Native American population grew 60-fold, starting 13-16 thousand years ago. Pigeon DNA shows no matching response. That suggests the net effect of Native activity on the pigeon population was neutral.

  The Wyandot, or Huron, believed that every twelve years, at the Feast of the Dead, the souls of the dead turned into passenger pigeons, which were then hunted and eaten. Before hunting young pigeons, the Seneca left an offering of wampum and brooches for the old birds beside a smoky fire. They believed a white pigeon led the colony and that a Council of Birds had decided the pigeons must give their bodies to the Seneca. The Seneca also developed a pigeon dance to show gratitude. The Ho-Chunk called the pigeon the bird of the chief, since it was served at his feasts.

  Some tribes moved closer to nesting colonies and killed juveniles at night with long poles. Many took care not to disturb the adults, and in some tribes disturbing them was a crime. Away from the nests, nets caught as many as 800 adults at a time. At one site in Oklahoma, the Cherokee threw clubs into the low-flying morning stream of birds. The lead pigeons veered aside and created a jam of easy targets. Among game birds in the southeastern United States, only the wild turkey mattered more. The bird's fat was stored and used like butter.

  Jacques Cartier reported passenger pigeons on his voyage in 1534. Samuel de Champlain and Cotton Mather later noted them too. Early accounts dwell on the countless numbers and the darkened skies. Colonists feared that large flights foretold misfortune or sickness, and some thought a winter outside the normal range meant a "sickly summer and autumn." In the eighteenth and nineteenth centuries, people used the blood for eye disorders and the powdered stomach lining for dysentery. The dung was used against headaches, stomach pains, and lethargy.

  In Saint-Jérôme, Quebec, every dowry for a time included a bed and pillows stuffed with pigeon feathers. The feathers did not last as long as goose feathers, but the demand was real. In 1822, one family in Chautauqua County, New York, killed 4,000 pigeons in a day solely for this purpose.

  Mark Catesby's 1731 illustration was the first published picture of the bird, though some later commentators called it crude. The British royal family bought his original watercolor in 1768. Alexander Wilson and John James Audubon both saw great migrations firsthand and tried to work out the numbers involved. Audubon's hand-colored aquatint in The Birds of America, issued between 1827 and 1838, is the most reproduced image. Craig and Shufeldt faulted it for showing two birds billing one above the other, and for the male's spread tail. They preferred the work of Louis Agassiz Fuertes and K. Hayashi. Most artists drew from stuffed birds. Only Charles R. Knight is known to have drawn the species from life, in 1903 and again at the Cincinnati Zoo, where he sketched a bird named Martha.

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• 8. Hunted to Extinction

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  In January 1565, the French explorer René Laudonnière described a "manna of wood pigeons" at Fort Caroline. His men shot more than two hundred a day with arquebuses for about seven weeks, close to 10,000 birds. That worked out to roughly one pigeon a day for each person in the fort. It may be the earliest account of Europeans hunting the species.

  After colonization, the hunting grew far more intensive than native methods. Settlements on the frontier relied on the meat. People fattened trapped birds before eating them, and they salted, pickled, or smoked the bodies for winter storage. In 1771-50,000 birds were reportedly sold at a Boston market. In the early nineteenth century, commercial hunters began netting and shooting pigeons to sell in city markets and even as pig feed.

  The birds were so easy to shoot that many people did not count them as game. An amateur could bring down six with a single blast, and a good shot with both barrels at a roost killed 61. Hunters fired skyward without aiming. They dug trenches and filled them with grain so pigeons lined up for the shot. Boys made a sport of it. In 1871, one ammunition seller supplied three tons of powder and 16 tons of shot during a single nesting.

  Live pigeons also served as targets in shooting tournaments, including trap-shooting with controlled releases. In one competition, 30,000 birds had to be killed to claim the prize. Nets propped open by a stick trapped twenty or more at a time, and one large tunnel net caught 3,500. Trappers baited with grain and salt, and at least one used alcohol-soaked grain to intoxicate the birds. Decoy "stool pigeons," sometimes blinded by sewing their eyelids shut, were tied to a stool and made to flutter down. Hunters poked nestlings out of nests, shot the bottoms of nests with blunt arrows, or felled one nesting tree onto another. In one case, 6 square kilometers of large trees were cut down for the birds.

  The decline came in two phases. A slow slide ran from about 1800 to 1870, and a rapid collapse followed between 1870 and 1890. Forest clearing destroyed habitat, and shrinking colonies fell below the size the species needed to survive. A plaque in Indiana states that the last confirmed wild passenger pigeon was shot in Laurel in 1902. Around the turn of the twentieth century, the last captive birds were split among three groups, and some were photographed alive.

  Martha, thought to be the last passenger pigeon, died at the Cincinnati Zoo on the 1st of September 1914. She was at least 17 and possibly as old as 29. In captivity, passenger pigeons could live at least fifteen years, but nobody knows how long wild ones lived. The loss stands as a notable example of extinction caused by humans.

  Walton Ford's 2002 painting Falling Bough is one modern work that still depicts the bird. The outreach group Project Passenger Pigeon used the centennial to spread awareness of human-induced extinction. Some have suggested the pigeon could serve as a flagship for other threatened North American birds. In 2014, John A. Ruthven, a winner of the National Medal of Arts, painted a mural in Cincinnati to mark the 100th anniversary of Martha's death.

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