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Conservation and Management
Effects Of Human Activity
“The pigeons were reduced by the destruction of the great forests that formerly fed them, destroyed by market hunters and netters, and finally, their vast flocks gone, broken up and scattered, the survivors roamed the country, targets for a million shotguns, until the inevitable end” (Forbush 1927: 79).
Ultimately, humans were the cause of extinction of Passenger Pigeons. How and why have been subject of much speculation. Bucher (1992) pointed out that there are 2 issues: the initial population decline and the inability of the species to persist at low numbers. Blockstein and Tordoff (1985) and Bucher (1992) provide competing hypotheses based on the unique ecological characteristics of Passenger Pigeons.
Two factors predominated in causing the decline: habitat destruction and direct exploitation by humans for food. It is likely that the interplay of these factors, with habitat destruction reducing opportunities for nesting, and shooting (Fig. 6; particularly at nesting colonies where in later years it caused abandonment of entire colonies), reduced the population size. Other explanations have been proposed, including climate, disease, and weather-related catastrophe, but there is no clear evidence for any of these (Bucher 1992).
Every Passenger Pigeon colony that was accessible to humans was exploited. Many archeological sites of native people in eastern North America include Passenger Pigeon remains (J. E. Ducey pers. comm.). There apparently was variation among tribes in the degree to which they disturbed nesting colonies or waited until the nestlings had reached sufficient size (see Kalm 1911, Fenton and Deardorff 1943). Many of the earliest writings of European colonists mention hunting of Passenger Pigeons either in transit or at nesting colonies or roosts. “When these roosts are first discovered, the inhabitants, from considerable distances, visit them in the night with guns, clubs, long poles, pots of sulphur, and various other engines of destruction. In a few hours, they fill many sacks and load their horses with them” (Wilson 1812: 104).
Commercial trade in pigeon meat, fat, and feathers began early in North American history. Professionals used massive nets (2 m wide × 6–10 m long) to capture live pigeons for sale to be used in shooting matches and to capture birds to be killed for market (Roney 1879). A large area, known as “the bed,” was cleared and prepared either by creating mud mixed with saltpeter and anise or by baiting a dried area with grain or even mast (Brewster 1889). Natural salt licks were also used. The net was laid alongside the bed and set by an adjustment of ropes and a powerful spring pole (Roney 1879). The operator sat in a blind made of boughs. A captured “stool pigeon” was used to help attract passing flocks. It was attached to a perch or box and manipulated to flap its wings or tossed from its tethered post into the air when a flock passed by. When the flock came to the bait, the net was sprung. As many as 10 “strikes” of the net were made at a single bed on 1 d, with “forty or fifty dozen” birds being a good haul for 1 strike, although twice as many could be captured at once (Brewster 1889). Pigeons were killed by pinching their necks or heads with pincers. This extensive killing probably had little, if any, impact on pigeon populations until the infrastructure was available to transport pigeons and carcasses from nesting colonies to markets in urban areas, beginning around 1840.
Blockstein and Tordoff (1985) argued that the development of the transcontinental railroad and the telegraph in the nineteenth century were key factors leading to extinction. Other authors also have mentioned the railroad as a factor (Forbush 1913, 1927; Brisbin 1968). Railroads allowed access to nesting colonies and the telegraph provided a way for scouts who located colonies to inform the professional pigeon trappers, who numbered some 600–1,200 men (Mann 1880–1881, Phillips 1907). “As settlement advanced, as railroads were built, spanning the continent, as telegraph lines followed them, as markets developed for the birds, an army of people, hunters, settlers, netters and Indians, found in the pigeons a considerable part of their means of subsistence, and the birds were constantly pursued and killed whenever they appeared, at all seasons of the year ” (Forbush 1927: 67).
In 1842, 3,000 live pigeons were transported by rail from Michigan to Boston. In 1851, an estimated 1,800,000 pigeons were sent to New York City from a nesting in n. New York (Schorger 1955: 145). By the time the Civil War ended, most of the U.S. east of the Mississippi was covered by railroad. Only a handful of nesting colonies was too far from rail or ship for market exploitation. Even a nesting in 1881 in Oklahoma, 176 km from the railroad, was pillaged by commercial trappers (Anon. 1881, Judy 1881).
Often hundreds of thousands of adults and squabs were shipped from a single nesting. Large numbers of birds were destroyed by locals or otherwise killed but not transported. A million birds could be lost at a single nesting. Yet even these large numbers of birds killed were probably not sufficient to cause the precipitous decline in the population. Overhunting did not exterminate the Passenger Pigeon as is commonly believed. Rather, the disturbance of the nesting colonies led the birds to abandon the nestings prematurely (Blockstein and Tordoff 1985). This, coupled with slaughter of nestlings as well as adults, largely eliminated replacement of the population. The first recorded abandonment of a nesting colony due to disturbance “by Indians and others” was in 1860 in Minnesota (Swanson 1940, from Mankato, MN, Record, 22 May, 1860). The last known attempt at a colonial nesting, in Wisconsin in 1887, also was abandoned. The birds left about 2 wk after they started to nest, probably due to the commotion from the shooting in the colony. In late Apr and early May 1888, “large flocks of pigeons” passed through Michigan. Professional netters prepared to capture birds at what they expected to be nesting colonies, but the birds passed north without nesting (Brewster 1889). Thus for nearly 30 yr, well over twice the lifetime of the average bird, there was a history of unsuccessful mass nestings. “The destruction of most of the young birds for a series of years would bring about such a diminution of the species as occurred soon after 1878” (Forbush 1913: 103). “The question often is asked, ‘how is it possible for man to kill them all?’ It was not possible, nor was it necessary that he should do so in order to exterminate them. All that was requisite to bring about this result was to destroy most of the young birds hatched each year. This was done year after year and nature cut off the rest” (Forbush 1927: 78).
Deforestation was also a major factor in the decline because it reduced the area available to the pigeons and thus reduced the opportunities for nesting and roosting colonies. Being nomadic, Passenger Pigeons needed enormous areas to find some conditions suitable for nesting (Askins 2000). Because nesting colonies formed only where there was sufficient mast, the reduction in the forest meant that in some years there was no nesting at all. Forbush (1927: 66) agreed that the decrease “was due in part to the destruction of the forests, particularly the beech woods. . . .” Another nineteenth-century technology, the portable saw mill introduced in 1870s, sped the destruction of what had once been a completely forested landscape. By 1880, about 80% of the original forest of New England had been cleared (Irland 1982). Deforestation in the major nesting area of north-central Pennsylvania began in 1872, but did not reach full speed until 1892 (French 1919: 110). Michigan was still well wooded in 1883 (Rand McNally and Co. 1883), although it was being logged rapidly, particularly for its pines, which would have had less impact on the Passenger Pigeon than logging of deciduous trees.
Deforestation, which occurred from east to west, reduced the available habitat. In the early eighteenth century, Wilson (1812: 109) noted that although the species was sometimes very numerous in the Atlantic states, it never appeared in “such unparalleled multitudes” of “congregated millions” as in the “western forests” of Ohio, Kentucky, and Indiana. The last recorded mass nesting in Massachusetts was in 1850s (Forbush 1927), in New York in the 1870s. From 1870 on, almost all of the nesting colonies recorded were in the forested Alleghenies of n. Pennsylvania and the Great Lake states of Michigan, Wisconsin, and, to a lesser extent, Minnesota (Mershon 1907). These were the areas where intact original forest remained (Williams 1989). In 1892, Bendire (1892: 132–133) wrote, “breeding range . . . principally in thinly settled and wooded region along our northern border . . . as well as . . . Canada, and north at least to Hudson Bay. Isolated and scattering pairs probably still breed in New England States, northern New York, Pennsylvania, Michigan, Wisconsin, Minnesota, and a few other localities further south, but the enormous breeding colonies . . . are . . . things of the past, probably never to be seen again. In fact, the extermination . . . has progressed so rapidly during the last twenty years that it now looks as if their total extermination might be accomplished in the present century.”
Schorger (1955) and Blockstein and Tordoff (1985) argued that the extent of mast-bearing forest in the 1870s and 1880s was sufficient to support the population. However it apparently was not enough to allow nesting colonies every year. After another 3 decades, there was essentially no sufficient forest left. But the pigeons were gone before the last deciduous forests. “The destruction of the forest was not yet complete; for, although great tracts of land were cleared, there remained and still remain vast regions more or less covered by coppice growth sufficient to furnish hosts of pigeons with food, and the cultivation of land and the raising of grain provided new sources of food supply. Therefore, while the reduction of the forest area in the east was a factor in the diminution of the pigeons, we cannot attribute their extermination to the destruction of the forest” (Forbush 1927: 66).
Bucher (1992) contended that reduced mast availability on the breeding grounds due to deforestation played a pivotal role in the decline, and particularly in the extinction. In his view, the original decline resulted from a combination of deforestation, competition with feral pigs for mast, and intensive hunting and disturbance of the nesting colonies. He postulated that a positive feedback from the initial decline coupled with increasing difficulty for colonies to find sufficient mast (due to a decreased population to search for a food resource that had been reduced due to deforestation) could explain the accelerating population decline in the 1870s. However, this period was also a time of increased disturbance and abandonment of nesting colonies, which was certainly also a factor.
Causes Of Extinction
“The most probable cause for the disappearance of the pigeon lies in the fact that, through the clearing of the forests and the increasing persecution by man, the birds were driven from one place to another and gradually compelled to nest farther and farther to the north, and under conditions successively less and less favorable, so that eventually the larger part of the great flocks consisted of old birds, which through stress of weather and persecution, abandoned their nesting places and failed to rear any considerable number of young” (Barrows 1912: 248).
Once the population reached a level of thousands, rather than billions, the species was unable to recover. Several factors may have been involved. Persecution continued, nearly to the end. In spring 1883, all of the young were reportedly taken. One man was said to have taken 60,000 and several others 10,000 young each (E. S. Bond in Anon. 1883). Over 5,000 birds were reportedly killed at a roost in Missouri the following winter (Anon. 1884). Over 1,000 carcasses were shipped to Boston in 1891 (Editor 1891 in Schorger 1955: 218). Market-hunting continued until at least 1893, and shooting was reported to the end.
Blockstein and Tordoff (1985) hypothesized that the species slowly faded away throughout its last decade. By 1892, “the majority [were] no longer breeding in colonies, but scattering around the country and breeding in isolated pairs” (Bendire 1892: 133). Since the species lacked the numbers for predator satiation through mass nesting that had been responsible for its success and had no antipredator adaptations for nesting, such as nest concealment, and since it laid only a single egg, nest success must have been insufficient to maintain the population.
In contrast, Bucher (1992: 25) argued that the decline in numbers circumvented the social facilitation necessary for the flocks to find enough mast for a successful nesting. In his view, once a population went below a minimum viable size, “the remaining individuals were unable to find food patches at [an] adequate rate.” He felt it “likely that a whole flock may have ‘missed’ good spots when moving north and starved or at least failed to produce enough offspring to compensate for adult mortality.” However, a smaller flock would need less food to sustain itself, and it seems likely that a pair could have found enough food (mast and crops) to eat and probably even to breed.
Both arguments are based on the inability of a small population to maintain itself after numbers were insufficient to achieve the evolved strategy essential to the success of the species—predator satiation (Blockstein and Tordoff 1985) or social facilitation of foraging (Bucher 1992). The unknowable true cause may have had elements of each. However, it is known that the pigeons continued to nest in colonies, even as late as 1885–1887 (Schorger 1955: 216). After that, there was at least some success in nesting in very small groups or even lone pairs (as always had been the case with a minuscule proportion of the population). The last birds collected in 1899 in Wisconsin and in 1900 in Ohio were both immatures.
The extinction of the Passenger Pigeon predated any conservation movement in America. The extinction of the once “limitless” flocks of pigeons, along with the near extermination of the American bison (Bison bison), introduced Americans to the concept of human-induced extinction. Some states approved laws regulating the location of nets away from nesting colonies, prohibiting disturbance at the nesting colony (within 3.2 km in Michigan), but these laws were rarely enforced (Roney 1879) and were, for the most part, too late. The density and abundance of the pigeons were such that few people recognized that there were any risks to the species. Arguments that there was no need for protection generally doomed any proposed legal protection (Forbush 1927).
“There will always be pigeons in books and museums, but these are effigies and images, dead to all hardships and to all delights. Book-pigeons can not dive out of a cloud to make the deer run for cover, or clap their wings in thunderous applause of mast-laden woods. Book-pigeons cannot breakfast on new-mown wheat in Minnesota, and dine on blueberries in Canada. They know no urge of seasons, no lash of wind and weather. They live forever by not living at all” (Leopold 1947).