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|Live passenger pigeon in 1896, kept by C.O. Whitman|
|Species:||† E. migratorius|
|Distribution map, with breeding zone in red and wintering zone in orange|
Some estimate 3 to 5 billion passenger pigeons were in the United States when Europeans arrived in North America.[B] Others argue the species had not been common in the pre-Columbian period, but their numbers grew when devastation of the American Indian population by European diseases led to reduced competition for food.[C]
The species went from being one of the most abundant birds in the world during the 19th century to extinction early in the 20th century. At the time, passenger pigeons had one of the largest groups or flocks of any animal, second only to the Rocky Mountain locust.
Some reduction in numbers occurred from habitat loss when European settlement led to mass deforestation. Next, pigeon meat was commercialized as a cheap food for slaves and the poor in the 19th century, resulting in hunting on a massive and mechanized scale. A slow decline between about 1800 and 1870 was followed by a catastrophic decline between 1870 and 1890. Martha, thought to be the world's last passenger pigeon, died on September 1, 1914, at the Cincinnati Zoo.
Taxonomy and systematics
The passenger pigeon was a member of the pigeon and dove family Columbidae and was originally described in 1766 as Columba migratoria by Carl Linnaeus. In 1827 William John Swainson moved the passenger pigeon from the genus Columba to the newly erected monotypic genus Ectopistes due in part to the greater length of the tail and wings, larger size, sexual dimorphism, and lack of a facial stripe. Many other scientific names have been applied, including names with the mourning dove's specific name macroura and Ectopistes canadensis, but have been rejected in favor of Ectopistes migratorius. It had no known subspecies.
The passenger pigeon's closest living relatives were originally thought to be the Zenaida doves, particularly the mourning dove, based on morphological grounds. The mourning dove was even suggested to belong to the genus Ectopistes and was listed by some authors as E. carolinensis. However, genetic analysis in 2010 demonstrated that the passenger pigeon was in fact closely related to the American Patagioenas pigeons, including western North America's band-tailed pigeon, to which the passenger pigeon may have been an eastern counterpart. Ectopistes and Patagioenas were shown to belong to a different clade of pigeons than the Zenaida doves, and were most closely related to the Southeast Asian cuckoo-doves in the genera Macropygia and Reinwardtoena. This group is also closely related to the Columba and Streptopelia doves of the Old World, and the passenger pigeon was able to hybridize with the Eurasian collared dove (Streptopelia decaocto) in captivity, though the offspring were infertile.
More than 130 passenger pigeon fossils have been found scattered across 25 states and provinces. These records date as far back as 100,000 years ago in the Pleistocene era, during which the pigeon's range extended at least to California and other Western states that were not a part of its modern range.
Etymology and usageThe common name "passenger pigeon" derives from the French word passager, which means "to pass by" in a fleeting manner. The generic epithet translates as "wandering about", the specific indicates it is migratory; the passenger pigeon's movements were not only seasonal, as with other birds, but they would also mass in whatever location was most productive and suitable for breeding. While the pigeon was extant, the name passenger pigeon was interchangeable with wild pigeon. It also gained a number of less-frequently used names, including blue pigeon, merne rouck pigeon, wandering long-tailed dove, and wood pigeon.
In the 18th century, the passenger pigeon in Europe was known to the French as tourtre; but, in New France, it was called tourte. Urban legend has it that in today's Canadian province of Quebec, the traditional meat pie called "tourtière" was once cooked with the bird, but the word could also be derived from Latin torta. In modern French, the bird is known as tourte voyageuse or pigeon migrateur, among other names.
In the native Algonquian languages, it was called amimi by the Lenape, omiimii by the Ojibwe, and mimi8a by the Kaskaskia Illinois. Other names in indigenous languages include ori'te in Mohawk, putchee nashoba, or lost dove, in Choctaw, and yu-ak-oo-was in Seneca.
The passenger pigeon was much larger than the somewhat similarly-plumaged mourning dove. Physically it was adapted for speed and maneuverability in flight, with a small head and neck, long and wedge-shaped tail, and long, broad, and pointed wings. It had particularly large breast muscles that enabled it to fly for long distances. The male was about 15.4 to 16.1 in (39 to 41 cm) long, while the female was slightly smaller at 14.9 to 15.7 in (38 to 40 cm) in length. The long, tapering tail accounted for much of this length as it was between 6.9 and 8.3 in (18 and 21 cm) long. It weighed between 9 and 12 oz (260 and 340 g). This pigeon had a carmine-red iris surrounded by a narrow purplish-red eyering. The bill was black, while the feet and legs were a bright coral red in the male, slightly duller in the female, and just a dull red in the juvenile.
The adult male passenger pigeon had a blueish-gray head, nape, and hindneck. On the sides of the neck and the upper mantle were display feathers that had a bright violet to golden-green iridescence. The upper back and wings were a pale gray that turned into grayish-brown on the lower wings. The bird's secondaries and primaries were a blackish-brown with a narrow white edge on the outer side of the feather. The greater and median wing-coverts were pale gray. The wing also had a small number of black spots. The back and rump were a dark blue-gray that became grayish-brown on the uppertail-coverts. The tail pattern was distinctive as it had white outer edges with blackish spots that were prominently displayed in flight. The lower throat and breast were richly pinkish-rufous and became a paler pink further down the belly. The undertail was white with a few black spots.
The adult female was browner on the upperparts and paler on the underparts than the adult male. The wings, back, and tail were similar in appearance to those of the male except that the outer edges of the primary feathers were edged in buff or rufous buff. The wings also had more spotting than those of the male. It was a grayish-brown on the forehead, crown, and nape down to the scapulars, and the feathers on the sides of the neck had less iridescence than those of the male. The lower throat and breast were a buff-gray that developed into white on the belly and undertail-coverts.
The juvenile was similar in plumage to the female, but lacked the spotting on the wings, and was a darker brownish-gray on the head, neck, and breast. The feathers on the wings had pale gray fringes to feathers, giving it a scaled look. The secondaries were brownish-black with pale edges, and the tertial feathers had a rufous wash. The primaries were also edged with a rufous-brown color. The neck feathers had no iridescence.
VoiceWhile many observers described the noise produced by flocks of passenger pigeons as deafening, the only scientific notes on the species' calls come from a small captive flock. Generally, the bird's voice was loud, harsh, and unmusical. One call was a simple harsh "keck" that could be given twice in succession with a pause in between. This was said to be used to attract the attention of another pigeon. A second call was the more frequent and variable scolding call. This call, described as "kee-kee-kee-kee" or "tete! tete! tete!", was used to either call to its mate or towards other creatures it considered to be enemies. One variant of this call, described as a long, drawn-out "tweet", could be used to call down a flock of passenger pigeons passing overhead, which would then land in a nearby tree. "Keeho" was a soft cooing that, while followed by louder "keck" notes or scolding, was directed at the bird's mate. A nesting passenger pigeon would also give off a stream of at least eight mixed notes that were both high and low in tone and ended with "keeho". Overall, female passenger pigeons were more quiet and called infrequently.
Distribution and habitat
The passenger pigeon was found across most of North America east of the Rocky Mountains. It originally bred from the southern parts of eastern and central Canada south to eastern Kansas, Oklahoma, Mississippi, and Georgia in the United States, but the primary breeding range was in southern Ontario and the Great Lakes states south through states north of the Appalachian Mountains. The pigeon wintered from Arkansas, Tennessee, and North Carolina south to Texas, the Gulf Coast, and northern Florida; however, flocks occasionally wintered as far north as southern Pennsylvania and Connecticut. There were also sightings of passenger pigeons outside of its normal range, including in several Western states, Bermuda, Cuba, and Mexico, particularly during severe winters. It has been suggested that some of these extralimital records may be considered extralimital more on the basis of the paucity of observers in what was then unsettled country than on the actual extent of wandering passenger pigeons, and that the bird may have appeared anywhere on the continent except for the Far West. There were also accidental records from Scotland, Ireland, and France, although these birds may have been escapees.
Its primary habitat was in eastern deciduous forests. During the day, it left the roosting forest to forage on more open land. Beeches and oaks produced the mast needed to support nesting and roosting flocks. It preferred to winter in large swamps, particularly those with alder trees; if swamps were not available, forested areas, particularly with pine trees, were favored roosting sites.
Ecology and behavior
The passenger pigeon was one of the most social land birds. It lived in colonies stretching over hundreds of square miles and practiced communal breeding with up to a hundred nests in a single tree. At the height of its population of three to five billion it may have been the most numerous bird on Earth, and A. W. Schorger believed that it accounted for between 25 and 40% of the total landbird population in the United States. Even today the passenger pigeon's historic population is roughly the equivalent of the number of birds that overwinter in the United States every year.
The passenger pigeon was nomadic and had no site fidelity, often choosing to nest in a different location each year. Pigeon migration, in flocks numbering billions, was a spectacle without parallel. John James Audubon described one flock he encountered with the words:
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 impracticable as the birds poured in in countless multitudes, I rose, and counting the dots then put down, found that 163 had been made in twenty-one minutes. I traveled on, and still met more the farther I proceeded. The air was literally filled with Pigeons; the light of noon-day was obscured as by an eclipse; the dung fell in spots, not unlike melting flakes of snow; and the continued buzz of wings had a tendency to lull my senses to repose... Before sunset I reached Louisville, distance from Hardensburgh fifty-five miles. The Pigeons were still passing in undiminished numbers, and continued to do so for three days in succession.Others frequently described these flocks as being so dense that they blackened the sky and as having no sign of subdivisions. The flocks ranged from only 3.3 ft (1.0 m) above the ground in windy conditions to as high as 1,300 ft (400 m). These migrating flocks were typically in narrow columns that twisted and undulated, but they were reported as being in nearly every conceivable shape.
The passenger pigeon was an excellent flyer, and is estimated to have averaged 62 mph (100 km/h) during migration. It flew with quick, repeated flaps that increased the birds velocity the closer the wings got to the body. It was equally as adept and quick at flying through a forest as through open space. A flock was also adept at following the lead of the pigeon in front of it, and flocks swerved together to avoid a predator. When landing, the pigeon flapped its wings repeatedly before raising them at the moment of landing. However, the pigeon was awkward when foraging on the ground, and used a "jerky, alert step" to move around. The pigeon bathed in shallow water, and afterwards lay on each side in turn and raised the opposite wing to dry it.
At roosting sites the passenger pigeons packed so densely on branches that even thick ones often broke under their collective weight. They often piled on top of each other's backs to roost. The pigeons rested in a slumped position that hid their feet. They slept with their bills concealed by the feathers in the middle of the breast while holding their tail at a 45-degree angle. Dung could accumulate under a roosting site to a depth of over 1 ft (0.30 m).
If the pigeon became alert, it would often stretch out its head and neck in line with its body and tail, then nodded its head in a circular pattern. When aggravated by another pigeon, it raised it wings threateningly, but passenger pigeons almost never actually fought.
Nesting colonies attracted large numbers of predators, including American minks, weasels, American martens, and raccoons that preyed on eggs and nestlings, predatory birds, such as owls, hawks, and eagles that preyed on nestlings and adults, and wolves, foxes, bobcats, bears, and mountain lions that preyed on injured adults and fallen nestlings. Accipiters and falcons pursued and preyed upon pigeons in flight, which in turn executed complex aerial maneuvers to avoid them; the Cooper's hawk was known as the "great pigeon hawk" due to its successes, and Cooper's hawks allegedly followed migrating passenger pigeons. It is believed that the large congregations of pigeons were based on the anti-predator benefits of very large numbers. While many predators were drawn to the flocks, individual pigeons were largely protected due to the sheer size of the flock, and overall little damage could be inflicted on the flock by predation. Despite the number of predators, nesting colonies were so large that they were estimated to have a 90% success rate if not disturbed.
In addition to attracting predators, the passenger pigeon hosted at least two species of parasite. One species of phtilopterid louse, Columbicola extinctus, was originally thought to have lived on just passenger pigeons and became extinct with them. However, this coextinction was proven inaccurate by 1999 when Columbicola extinctus was rediscovered living on band-tailed pigeons. Another louse, Campanulotes defectus, was thought to have been unique to the passenger pigeon; however, it is now believed to have been a case of a contaminated specimen as the species is now considered to be the still-extant Campanulotes flavus of Australia. There is no record of a wild pigeon dying of either disease or parasites.
One of the primary causes of natural mortality was the weather, and every spring many individuals froze to death after migrating north too early. In captivity, a passenger pigeon was capable of living at least 15 years; Martha, the last known living passenger pigeon, was at least 17 and possibly as old as 29 when she died. However, it is unknown how long a wild pigeon lived.
The bird is believed to have played a large ecological role in the composition of presettlement forests of eastern North America. For instance, forests while the passenger pigeon was extant were dominated by white oaks. This species germinated in the fall, therefore producing acorns during the spring to be devoured and spread by the pigeons. The absence of the passenger pigeon's seed dispersal may have led to the modern dominance of red oaks. At roosting sites, few plants grew for years after the pigeons left. Additionally, the immense amount of dung present at these sites increased both the frequency and intensity of forest fires.
DietThe passenger pigeon changed its diet depending on the season. In the fall, winter, and spring, it mainly ate beechnuts, acorns, and chestnuts. During the summer, berries and softer fruits, such as blueberries, grapes, cherries, mulberries, pokeberries, and the fruit of dogwoods, became the main objects of its consumption. It also ate earthworms, caterpillars, and snails, particularly while breeding. Additionally, the passenger pigeon took advantage of cultivated grains, particularly buckwheat, when it found them. The species was particularly fond of salt, which it ingested either from brackish springs or salty soil.
The passenger pigeon foraged in flocks of tens or hundreds of thousands of individuals that overturned leaves, dirt, and snow with their bills in a frantic search for nuts. These flocks had a rolling appearance as birds in the back of the flock flew overhead to land at the front of the flock, dropping leaves and grass in flight. They also had wide leading edges in order to better scan the landscape for food sources. When nuts on a tree loosened from their caps, a pigeon would land on a branch and, while flapping vigorously to stay balanced, grab the nut, pull it loose from its cap, and swallow it whole. Collectively, a foraging flock was capable of removing nearly all fruits and nuts from their path. Birds in the back of the flock flew to the front in order to pick over unsearched ground; however, birds never ventured far from the flock and hurried back if they became isolated. It is believed that the pigeons used social cues in order to identify abundant sources of food, and a flock of pigeons that saw others feeding on the ground often joined them. They regularly flew 62 to 81 mi (100 to 130 km) away from their roost daily in search of food, and some pigeons reportedly traveled as far as 100 mi (160 km).
After feeding, the pigeons perched on branches and digested their food, which they had stored in their crops. This crop was capable of expanding to about the size of an orange; this allowed a bird to quickly grab any food it discovered in the highly competitive flock. The crops were described as being capable of holding at least 17 acorns or 28 beechnuts, 11 grains of corn, 100 maple seeds, plus other material; it was estimated that a passenger pigeon needed to eat about 3.7 in3 (61 cm3) of food a day in order to survive, all of which was digested overnight. At the historic population of three billion passenger pigeons, this amounted to 55,000,000 US gal (210,000,000 L) of food a day. The pigeon was also able to regurgitate food from its crop when more desirable food became available.
The passenger pigeon drank at least once a day, typically at dawn, by fully inserting its bill into lakes, small ponds, and streams. Pigeons were seen perching on top of each other in order to gain access to water, and if necessary, the species could alight on open water to drink.
The formation of a nesting colony did not necessarily take place until several months after the pigeons arrived on their breeding grounds, typically during late March, April, or May. The colonies, which were known as cities, were immense, ranging from 120 acres (49 ha) to thousands of hectares in size, and were often long and narrow in shape. Due to the topography, they were rarely continuous. Since no accurate data were recorded, it is not possible to give more than estimates on the size and population of these nesting areas. The largest nesting area ever recorded was in central Wisconsin in 1871; it was reported as covering 850 sq mi (2,200 km2), with the number of birds nesting there estimated to be around 136,000,000. In addition to these cities, there were regular reports of much smaller flocks or even individual pairs setting up a nesting site.
Courtship took place at the nesting colony. John James Audubon described the courtship of the passenger pigeon as:
The male assumes a pompous demeanor, and follows the female, whether on the ground or on the branches, with spread tail and drooping wings, which it rubs against the part over which it is moving. The body is elevated, the throat swells, the eyes sparkle. He continues his notes, and now and then rises on the wing, and flies a few yards to approach the fugitive and timorous female. Like the domestic Pigeon and other species, they caress each other by billing, in which action, the bill of the one is introduced transversely into that of the other, and both parties alternately disgorge the contents of their crop by repeated efforts.Captive passenger pigeons did not perform the bowing, strutting, and billing described by Audubon, and there is some debate over the accuracy of Audubon's description. Unlike other pigeons, courtship took place on a branch or perch. The male, with a flourish of the wings, made a "keck" call while near a female. He then gripped tightly to the branch and vigorously flapped his wings up and down. When he was close to the female, the male then pressed against her on the perch with his head held high and pointing at her. If receptive, the female pressed back against the male. As both pigeons took care of the nest, the pairs were monogamous for the duration of the nesting.
When ready to mate, the pair preened each other. This was followed by the birds billing, in which the female inserted her bill into and clasped the male's bill, shook for a second, and separated quickly while standing next to each other. The male then scrambled onto the female's back and copulated, which was then followed by soft clucking and occasionally more preening.
Nests were built immediately after pair formation and took two to four days to construct; this process was highly synchronized within a colony. Nearly every tree capable of supporting nests had them, often more than 50 per tree; one hemlock was recorded as holding 317 nests. The female chose the nesting site by sitting on it and flicking her wings. The male then carefully selected nesting materials, typically twigs, and handed them to the female over her back. He then went in search of more nesting material while the female constructed the nest beneath her. Nests were built between 6.5 and 66 ft (2.0 and 20.1 m) above the ground, though typically above 13 ft (4.0 m), and were made of 70 to 110 twigs woven together to create a loose, shallow bowl through which the egg could easily be seen. This bowl was then typically lined with finer twigs. The nests were about 6 in (15 cm) wide, 2.4 in (6.1 cm) high, and 0.75 in (1.9 cm) deep.
Generally, the eggs were laid during the first two weeks of April across the pigeon's range. Each female laid a single egg immediately or almost immediately after the nest was completed; sometimes the pigeon was forced to lay it on the ground if the nest was not complete. Occasionally, a second female laid her egg in another female's nest, resulting in two eggs being present. The egg was white and oval shaped and averaged 1.56 in (40 mm) by 1.32 in (34 mm) in size. If the egg was lost, it was possible for the pigeon to lay a replacement egg within a week. A whole colony was known to renest after a snowstorm forced them to abandon their original colony. The egg was incubated for 12 to 14 days, with the male incubating it from midmorning to midafternoon and the female incubating it for the rest of the time.
Upon hatching, the nestling was blind and covered sparsely only with yellow, hairlike down. It developed quickly and within 14 days weighed as much as its parents. During this brooding period both parents took care of the nestling, with the males attending for midday. The nestlings were fed crop milk exclusively for the first three or four days. After 13 to 15 days, the parents abandoned their nestling, which begged in the nest for a day before fluttering to the ground and begging for food from nearby adults. It was another three or four days before it fledged. The nesting colonies broke up after the nestlings fledged, and it is unknown whether colonies renested after a successful nesting. The passenger pigeon sexually matured during its first year and bred the following spring.
Relationship with humans
The passenger pigeon played a religious role in some northern Native American tribes. The Huron believed that every twelve years during the Feast of the Dead, the souls of the deceased changed into passenger pigeons, which were then hunted and eaten. Before hunting the juvenile pigeons, the Seneca made an offering to the old passenger pigeons, an offering of wampum and brooches that were placed in a small kettle or other receptacle by a smoky fire. The Ho-Chunk considered the passenger pigeon to be the bird of the chief, as they were served whenever the chieftain gave a feast.
The Seneca believed that a white pigeon was the chief of the passenger pigeon colony, and that a Council of Birds had decided that the pigeons had to give their bodies to the Seneca because they were the only bird that nested in colonies. The Seneca developed a pigeon dance as a way of showing their gratitude.
The early colonists thought that large flights of pigeons would be followed by ill fortune or sickness. When the pigeons wintered outside of their normal winter range, some believed that they would have "a sickly summer and autumn."
The flavor of the flesh of passenger pigeons varied depending on how they were prepared. In general, juveniles were thought to taste the best, followed by birds fattened in captivity and birds caught in September and October. The fat was also kept as butter.
Though they did not last as long as the feathers of a goose, the feathers of the passenger pigeon were frequently used for bedding. Pigeon feather beds were so popular that for a time in Saint-Jérôme, Quebec, every dowry included a bed and pillows made of pigeon feathers. In 1822, one family in Chautauqua County, New York, killed 4,000 pigeons in a day solely for their feathers.
In the 18th and 19th centuries, various parts of the pigeon were alleged to have medicinal properties. The blood was supposed to be good for eye disorders, the powdered stomach lining was used to treat dysentery, and the dung was used to treat a variety of ailments, including headaches, stomach pains, and lethargy.
The passenger pigeon was an important source of food for the people of North America. The Native Americans ate passenger pigeons, and tribes near nesting colonies would sometimes move to live closer to them and eat the juveniles. The juveniles were killed at night with long poles. Most Native Americans were careful not to disturb the adult pigeons, and instead ate only the juveniles as they were afraid that the adult pigeons might desert their nesting grounds; in some tribes disturbing the adult pigeons was considered a crime. Away from the nests, large nets were used to capture adult pigeons, sometimes up to 800 at a time. Among the game birds, passenger pigeons were second only to the wild turkey in terms of importance for the Native Americans living in the southeastern United States. The bird's fat was stored, often in large quantities, and used as butter. Archaeological evidence supports the idea that the Native American ate the pigeons frequently prior to colonization.
After colonization, the passenger pigeon was an important source of food for the poor or common people due to its availability and low cost. It was of particular value on the frontier, and some colonies counted on the pigeon to support their population.
In the early 19th century, commercial hunters began netting and shooting the birds to sell in city markets as food, as live targets for trap shooting, and even as food for pigs. Once pigeon meat became popular, commercial hunting started on a prodigious scale. John James Audubon described the preparations for slaughter at a known pigeon-roosting site:
Few pigeons were then to be seen, but a great number of persons, with horses and wagons, guns and ammunition, had already established encampments on the borders. Two farmers from the vicinity of Russelsville, distant more than a hundred miles, had driven upwards of three hundred hogs to be fattened on the pigeons which were to be slaughtered. Here and there, the people employed in plucking and salting what had already been procured, were seen sitting in the midst of large piles of these birds. The dung lay several inches deep, covering the whole extent of the roosting-place.One method of capture was to hunt at a nesting colony, particularly during the period of a few days after the adult pigeons abandoned their nestlings but before the nestlings could fly. Some hunters used sticks to poke the nestlings out of the nest, while others shot the bottom of a nest with a blunt arrow to dislodge the pigeon. Others cut down a nesting tree in such a way that when it fell, it would also hit a second nesting tree and dislodge the pigeons within. An extreme method, practiced only by particularly unscrupulous hunters, was to set fire to the base of a tree nested with pigeons; the adults would flee and the juveniles would fall to the ground, bursting open.
There were a wide variety of other methods that were used to capture and kill passenger pigeons. Sulfur was sometimes burned beneath the nesting tree to suffocate the birds, which fell out of the tree in a weakened state. At least one trapper used alcohol-soaked grain as bait to intoxicate the birds and make them easier to kill. Salt was also frequently used as bait, and many trappers set up near salt springs. Stool pigeons, which traditionally were blinded, were also used to attract flocks of pigeons that thought that the stool pigeon had found food.
Low-flying pigeons could be killed by thrown sticks or stones. At one site in Oklahoma, the pigeons leaving their roost every morning flew low enough that the Cherokee could throw clubs into their midst, which caused the lead pigeons to try to turn aside and in the process created a blockade that created a large mass of flying, easily hit pigeons.
Nets were propped up to allow passenger pigeons entry, then closed by knocking loose the stick that supported the opening, trapping twenty or more pigeons inside. Tunnel nets were also used to great effect, and one particularly large net was capable of catching 3,500 pigeons at a time. These nets were used by many farmers on their own property as well as by professional trappers.
Passenger pigeons were shot with such ease that many did not consider them to be a game bird, as an amateur hunter could easily bring down six with one shotgun blast; a particularly good shot with both barrels of a shotgun at a roost could kill 61 birds. They were frequently shot either in flight during migration or immediately after, when they traditionally perched in dead, exposed trees. The pigeons did prove difficult to shoot head-on, so hunters typically waited for the flocks to pass overhead before shooting them. Trenches were sometimes dug and filled with grain so that a hunter could shoot the pigeons along this trench.
Hunters largely outnumbered the trappers, and hunting passenger pigeons was a popular sport for young boys. At a nesting site in Petoskey, Michigan, in 1878, 50,000 birds were killed each day for nearly five months. The surviving adults attempted a second nesting at new sites, but were killed by professional hunters before they had a chance to raise any young. Neltje Blanchan documented that over a million birds could be exterminated at one time from a single flock, and that an equal number were left either wounded or orphaned before they could fend for themselves. Paul R. Ehrlich reported that a "single hunter" sent three million birds to eastern cities during his career.
It was common practice to fatten trapped pigeons before eating them or storing their bodies for winter. Dead pigeons were commonly stored by salting or pickling the bodies; other times, only the breasts of the pigeons were kept, in which case they were typically smoked.
By the mid-1800s, railroads had opened new opportunities for pigeon hunters. While previously it proved too difficult to ship masses of pigeons to eastern cities, the access provided by the railroad permitted pigeon hunting to become commercialized. After being opened up to the railroads, the town of Plattsburg, New York, is estimated to have shipped 1.8 million pigeons to larger cities in 1851 alone at a price of 31 to 56 cents a dozen.
By the late 1800s, the trade of passenger pigeons had become commercialized. Large commission houses employed trappers to follow the flocks of pigeons year-round. In 1874, at least 600 individuals were employed as pigeon trappers, a number which grew to 1,200 by 1881. Pigeons were so commonplace that by 1876, shipments of dead pigeons were unable to recoup the costs of the barrels and ice needed to ship them, which led to the pigeons being caught alive instead.
The extinction of the passenger pigeon had two major causes: commercial exploitation of pigeon meat on a massive scale and loss of habitat. In 2014, DNA genetic studies between preserved specimens and domestic pigeons performed by Chih-Ming Hung, a biologist at National Taiwan Normal University in Taipei and reported in the Proceedings of the National Academy of Sciences suggest that the passenger pigeons’ extinction may not have been solely due to human influence. Instead, the effects of an already natural population decline coupled with the pressures of hunting and population loss may have all contributed. “If it’s already on this track, human influence can further increase the speed that the population goes down,” Hung says. “And once it gets down to some really low level, there’s no way for the birds to recover.” 
Large flocks and communal breeding made the species highly vulnerable to hunting. As the flocks dwindled in size, populations decreased below the threshold necessary to propagate the species. Naturalist Paul R. Ehrlich wrote that its extinction "illustrates a very important principle of conservation biology: it is not always necessary to kill the last pair of a species to force it to extinction."
Another significant reason for its extinction was deforestation. The birds traveled and reproduced in prodigious numbers, satiating predators before any substantial negative impact was made in the bird's habitat. Reports of an abundance of passenger pigeons in forests were reported as late as 1871.
In 1857, a bill was brought forth to the Ohio State Legislature seeking protection for the passenger pigeon. A Select Committee of the Senate filed a report stating, "The passenger pigeon needs no protection. Wonderfully prolific, having the vast forests of the North as its breeding grounds, traveling hundreds of miles in search of food, it is here today and elsewhere tomorrow, and no ordinary destruction can lessen them, or be missed from the myriads that are yearly produced."
Conservationists were ineffective in stopping the slaughter. A bill was passed in the Michigan legislature making it illegal to net pigeons within two miles (3 km) of a nesting area, but the law was weakly enforced. By the mid-1890s, the passenger pigeon almost completely disappeared. In 1897, a bill was introduced in the Michigan legislature asking for a 10-year closed season on passenger pigeons. This was a futile gesture. Similar legal measures were passed and disregarded in Pennsylvania. This was a highly gregarious species – the flock could initiate courtship and reproduction only when they were gathered in large numbers; smaller groups of passenger pigeons could not breed successfully, and the surviving numbers proved too few to re-establish the species. Attempts at breeding among the captive population also failed for the same reasons. The passenger pigeon was a colonial and gregarious bird practicing communal roosting and communal breeding and needed large numbers for optimum breeding conditions.
The extinction of the passenger pigeon aroused public interest in the conservation movement, and resulted in new laws and practices which prevented many other species from becoming extinct. Naturalist Aldo Leopold paid tribute to the vanished species in a monument dedication held by the Wisconsin Society for Ornithology at Wyalusing State Park, Wisconsin, which had been one of the species' social roost sites. Speaking on May 11, 1947, Leopold remarked:
Men still live who, in their youth, remember pigeons. Trees still live who, in their youth, were shaken by a living wind. But a decade hence only the oldest oaks will remember, and at long last only the hills will know.
The last fully authenticated record of a wild bird was near Sargents, Pike County, Ohio, on March 22 or 24, 1900, when the bird was killed by a boy named Press Clay Southworth with a BB gun. Sightings continued to be reported in the 20th century, up until 1930. All sightings after the Ohio bird, however, are unconfirmed, in spite of rewards offered for a living specimen.
Reports of passenger pigeon sightings kept coming in from Arkansas and Louisiana, in groups of tens and twenties, until the first decade of the 20th century.
The naturalist Charles Dury, of Cincinnati, Ohio, wrote in September 1910: "One foggy day in October 1884, at 5 a.m. I looked out of my bedroom window, and as I looked six wild pigeons flew down and perched on the dead branches of a tall poplar tree that stood about one hundred feet away. As I gazed at them in delight, feeling as though old friends had come back, they quickly darted away and disappeared in the fog, the last I ever saw of any of these birds in this vicinity."
By the turn of the 20th century, the last known group of passenger pigeons was kept by Professor Charles Otis Whitman at the University of Chicago. Whitman studied these pigeons along with rock doves and Eurasian collared doves. All of Whitman's pigeons were descended from the same pair. Whitman and the Cincinnati Zoo attempted to breed the surviving birds, including attempts at making a rock dove foster passenger pigeon eggs. Whitman sent a female named Martha to the Cincinnati Zoo in 1902. While Whitman had about a dozen passenger pigeons in 1903, they had stopped breeding, and by 1906 he was down to five birds.
On September 1, 1914, Martha, the last known passenger pigeon, died in the Cincinnati Zoo. Her body was frozen into a block of ice and sent to the Smithsonian Institution, where it was skinned, dissected, photographed and mounted. Currently, Martha is on display through September 2015 as part of the Once There Were Billions exhibit at the Smithsonian National Museum of Natural History. A memorial statue of Martha stands on the grounds of the Cincinnati Zoo.
(According to a 1915 article in the New York Press, the last passenger pigeon died in Chicago earlier in the year at the age of 27.)
John Herald, a bluegrass singer, wrote a song dedicated to the extinction of the species and Martha, the species' endling, that he titled "Martha (Last of the Passenger Pigeons)".