Some estimate that there were as many as five billion passenger pigeons in the United States at the time Europeans arrived in North America. Others argue that 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.
During the 19th century, the species went from being one of the most abundant birds in the world to extinction. At the time, passenger pigeons had one of the largest groups or flocks of any animal, second only to the desert locust. They became such a threat to farmers that in 1703 the Roman Catholic bishop of Quebec actually formally excommunicated the species.
Some reduction in numbers occurred as a result of loss of habitat, when the Europeans started settling further inland. However, the primary factor emerged when pigeon meat was commercialized as a cheap food for slaves and the poor in the 19th century, resulting in hunting on a massive scale. There was a slow decline in their numbers between about 1800 and 1870, followed by a catastrophic decline between 1870 and 1890. "Martha", thought to be the world's last passenger pigeon, died on September 1 1914 in Cincinnati, Ohio.
In the 18th century, the passenger pigeon in Europe was known to the French as "tourtre" but in New France, the North American bird was called "tourte". In modern French, the bird is known as the pigeon migrateur.
During summer, passenger pigeons lived in forest habitats throughout North America east of the Rocky Mountains: from eastern and central Canada to the northeast United States. In the winters, they migrated to the southern U.S. and occasionally to Mexico and Cuba.
The passenger pigeon was a very social bird. It lived in colonies stretching over hundreds of square miles, practicing communal breeding with up to a hundred nests in a single tree. Pigeon migration, in flocks numbering billions, was a spectacle without parallel:
Early explorers and settlers frequently mentioned passenger pigeons in their writings. Samuel de Champlain in 1605 reported "countless numbers," Gabriel Sagard-Theodat wrote of "infinite multitudes," and Cotton Mather described a flight as being about a mile in width and taking several hours to pass overhead. Yet by the early 1900s no wild passenger pigeons could be found. — The Smithsonian Encyclopedia
Even prior to colonization, native Americans occasionally used pigeons for meat. In the early 1800s, commercial hunters began netting and shooting the birds to sell in the city markets as food, as live targets for trap shooting and even as agricultural fertilizer.
Once pigeon meat became popular, commercial hunting started on a prodigious scale. The bird painter 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.Pigeons were shipped by the boxcar-load to the Eastern cities. In New York City, in 1805, a pair of pigeons sold for two cents. Slaves and servants in 18th and 19th century America often saw no other meat. By the 1850s, it was noticed that the numbers of birds seemed to be decreasing, but still the slaughter continued, accelerating to an even greater level as more railroads and telegraphs were developed after the American Civil War. Three million pigeons were shipped by a single market hunter in the year 1878. 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 population. As their numbers decreased along with their habitat, the birds could no longer rely on high population density for protection. Without this mechanism, many ecologists believe, the species could not survive.
Possibly, the birds may have suffered from Newcastle disease, an infectious bird disease that was introduced to North America; though the disease was identified in 1926, it has been posited as one of the factors leading to the extinction of the passenger pigeon.
Attempts to revive the species by breeding the surviving captive birds were not successful. The passenger pigeon was a colonial and gregarious bird practicing communal roosting and communal breeding and needed large numbers for optimum breeding conditions. It was impossible to reestablish the species with just a few captive birds, and the small captive flocks weakened and died. Since no accurate data were recorded, it is only possible to give estimates on the size and population of these nesting areas. Each site may have covered many thousands of acres and the birds were so congested in these areas that hundreds of nests could be counted in each tree. One large nesting in Wisconsin was reported as covering 850 square miles, and the number of birds nesting there was estimated to be around 136,000,000. Their technique of survival had been based on mass tactics. There was safety in large flocks which often numbered hundreds of thousands of birds. When a flock of this huge a size established itself in an area, the number of local animal predators (such as wolves, foxes, weasels, and hawks) was so small compared to the total number of birds that little damage would be inflicted on the flock as a whole. This colonial way of life and communal breeding became very dangerous when man became a predator on the flocks. When the passenger pigeons were massed together, especially at a huge nesting site, it was easy for man to slaughter them in such great numbers that there were not enough birds left to successfully reproduce the species. As the flocks dwindled in size with resulting breakdown of social facilitation, it was doomed to disappear.
The extinction of the passenger pigeon aroused public interest in the conservation movement and resulted in new laws and practices which have prevented many other species from going extinct.
One method of killing was to blind a single bird by sewing its eyes shut using a needle and thread. This bird's feet would be attached to a circular stool at the end of a stick that could be raised five or six feet in the air, then dropped back to the ground. As the bird attempted to land, it would flutter its wings, thus attracting the attention of other birds flying overhead. When the flock landed near this decoy bird, nets would trap the birds and the hunters would crush their heads between their thumb and forefinger. This has been claimed as the origin of the term stool pigeon, though this etymology is disputed.
One of the last large nestings of passenger pigeons was at Petoskey, Michigan, in 1878. Here 50,000 birds were killed each day and the hunt continued for nearly five months. When the adult birds that survived the slaughter attempted second nestings at new sites, they were located by the professional hunters and killed before they had a chance to raise any young. In 1896, the final flock of 250,000 were killed by American sportsmen knowing that it was the last flock of that size. Conservationists were ineffective in stopping the slaughter. A bill was passed in the Michigan legislature making it illegal to net pigeons within two miles of a nesting area, but the law was weakly enforced. By the mid 1890s, the passenger pigeon had almost completely disappeared. It was too late to protect them by passing laws. In 1897, a bill was introduced in the Michigan legislature asking for a ten-year closed season on passenger pigeons. This was a futile gesture. A highly gregarious species, the flock could initiate courtship and reproduction only when they were gathered in large numbers; it was realized only too late that 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 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.
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"
Fifty-seven years later, on September 1, 1914, Martha, the last known passenger pigeon, died in the Cincinnati Zoo, Cincinnati, Ohio. Her body was frozen into a block of ice and sent to the Smithsonian Institution, where it was skinned and mounted. Currently, Martha (named after Martha Washington) is in the museum's archived collection, and not on display.
The dramatic story of the passenger pigeon has taken a strong hold on popular imagination.