One of the most dramatic extinctions in recent times underlines the importance of species protection
“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.”
Echoed through time are the words of John James Audubon, iconic American ornithologist, who, in the autumn of 1813, watched a flock of passenger pigeons fly over the Ohio countryside. Its numbers were so vast, he recounted, that it took more than three days for the birds pass overhead.
“I cannot describe to you the extreme beauty of their aerial evolutions, when a Hawk chanced to press upon the rear of a flock,” he wrote. “At once, like a torrent, and with a noise like thunder, they rushed into a compact mass, pressing upon each other towards the centre. In these almost solid masses, they darted forward in undulating and angular lines, descended and swept close over the earth with inconceivable velocity, mounted perpendicularly so as to resemble a vast column, and, when high, were seen wheeling and twisting within their continued lines, which then resembled the coils of a gigantic serpent.”
Hunters used large nets to catch passenger pigeons in the 1800s.
Then on September 1, 1914, just over one hundred years after Audubon’s account and exactly one hundred years ago today, the last member of what may have been the most numerous bird species on the planet died in a cage in the Cincinnati zoo.
The passenger pigeon (Ectopistes migratorius) was once the most common bird in North America, comprising an estimated 20 to 40 percent of the entire avian population of the United States. Ranging east of the Rocky Mountains from central Canada to the southern U.S., flocks were purported to contain millions of birds, with some reports counting billions in a single, “infinite” mass. They ate acorns whole, built hundreds of nests in a single tree, and could fly 100 kilometers per hour (62 mile per hour).
“A velocity such as this would enable one of these birds, were it so inclined, to visit the European continent in less than three days,” wrote Audubon.
And yet, even with seemingly inexhaustible numbers and an ability to travel great distances to find food, they went from billions to extinction in less than a century. The exact reasons as to how this could happen are still being investigated to this day, but one thing seems certain – humans most definitely had a hand in propelling the species to oblivion. The birds were very vulnerable to commercial hunting, with hundreds of nestlings harvested in the felling of a single tree. Tunnel nets were often used by hunters and farmers, and could catch 3,500 birds at a time. Pigeons were shot, clubbed, and intoxicated with alcohol-soaked grain, then pickled, smoked, and salted for winter stores.
 Passenger pigeons were somewhat “sexually dimorphic,” with the males more colorful than the females. Painting by John James Audubon. |
Railroad expansion in the mid-1800s made it easier to transport killed pigeons from the relatively unpopulated U.S. Midwest to the more lucrative East Coast markets, with 1.8 million pigeons shot and shipped in 1851 alone. In the 1870s the birds were still so common that the prices they fetched at market weren’t enough to pay for the costs of the barrels and ice needed to ship them, leading to a shift to live-caught birds.
However, by the 1890s, it was becoming very clear that the species was in trouble. Already extirpated from the East Coast, pigeon populations completely crashed in the Midwest over the course of just ten years.
“Extinction of the Passenger Pigeon came with stunning rapidity,” write biologist Paul R. Ehrlich and colleagues in a 1988 essay. “Michigan was its last stronghold; about three million birds were shipped east from there by a single hunter in 1878. Eleven years later, 1889, the species was extinct in that state.”
Efforts were made to head off extinction, with a bill brought forth to the Ohio State Legislature seeking protection for the species. However, the proposal was denied, with a Senate report stating the passenger pigeon “is here today and elsewhere tomorrow, and no ordinary destruction can lessen them, or be missed from the myriads that are yearly produced.”
While that view today may seem shortsighted, ill-informed, and full of sad irony, the fact is at that time no research had been done that could have predicted with any certainty the extinction of the passenger pigeon. Even now, advancements in the field of conservation genetics and the rebounding of California condors, kakapos, and other species decimated to a handful of individuals are showing that many species can recover from very low population sizes.
However, some research indicates that not all species can bounce back. Social species that evolved to live in large numbers can have very precarious population structures, so that even relatively low reductions may lead to collapse. A concept called the “Allee effect” first proposed in the 1940s but not extensively studied until 50 years later uses the observation that not all of the adult members in a social population are breeders, yet still may have important roles in ensuring the population’s survival. One such social species is the Seychelles warbler (Acrocephalus sechellensis), in which many individuals do not breed but instead help others in a colony raise their young.
 Pigeons were shot by the millions. While hunting alone was not responsible for their extinction, it played a big role in their decline. |
Studies have implicated the Allee effect in the demise of the passenger pigeon. As human hunting started taking larger and larger chunks out of pigeon populations, and clearing of forests removed the beech, maple, and chestnut trees that provided the pigeons with their preferred foods, flocks were reduced to sizes that were just too small to survive. According to a study published in Current Ornithology, a small flock has fewer eyes, thus reducing its chances of finding trees in seed. A small flock also has fewer experienced, older members that know where and when to fly.
However, even in captivity small flocks could not be sustained.
“Although small groups of pigeons were held in various places in captivity, efforts to maintain those flocks failed,” write Ehrlich and his colleagues.
The last verified report of a passenger pigeon in the wild was in Ohio in 1900, where a boy shot one with a BB gun. Anecdotal sightings occurred until 1930, but none were confirmed. The last-known captive flock was kept in Chicago, but slowly whittled down as the birds refused to breed. One from this flock, a female named Martha, was sent to the Cincinnati Zoo in 1902 (however, some reports state she was hatched at the zoo) where she was housed with a handful of males. By 1910 the males had all died, and the zoo was offering a $1,000 reward (approximately $25,000 today) for the capture of another despite Martha’s official status as the last of her kind.
Then, on September 1, 1914, Martha’s caretaker found her dead on the floor of her cage. Her generally accepted age at death was 29 years. Her body was quickly frozen in a 300-pound block of ice and sent to the Smithsonian, where she was stuffed and put on display. Currently, she is being used in a special exhibit about passenger pigeons called “Once There Were Billions,” which will run until Sept 2015.
Since the demise of the passenger pigeon, the world has taken steps to protect its most vulnerable denizens such as the 1973 passage of the U.S. Endangered Species Act (ESA).
“This nation enacted the ESA so that we would never again experience a loss like the passenger pigeon, a human-caused extinction that could have been prevented,” said Jamie Rappaport Clark, president and CEO of Defenders of Wildlife. “Indeed, had the ESA been in place in the late 19th century, it likely would have saved the passenger pigeon. Though the ESA came too late to save Martha’s species, today we can look to it as a statement of America’s commitment to protecting our nation’s imperiled wildlife and plants for future generations.
 Martha, the last recorded passenger pigeon on Earth. She was named after Martha Washington. |
Today we live in what scientists term the “Sixth Great Extinction,” and studies estimate the world may be losing thousands of species every year — mostly due to human activity. Through hunting, deforestation, emission of greenhouse gases, and transmission of disease (among others), with casualties ranging from the megafauna of the Pleistocene to the golden toad of Costa Rica’s cloud forests, humans are changing the natural world at a rate that is unprecedented.
Yet, despite mounting threats to many species, policies that regulate human impact on the environment are still being challenged.
“Sadly, even after all we’ve learned about the critical importance of this landmark law, the ESA is on the chopping block in Congress once again,” Rappaport Clark said. “Too often, we have seen members of Congress move to dismantle key pieces of the ESA and gut protections for imperiled wildlife, rejecting the very conservation values that are the foundation of the ESA.
“It’s my hope that the haunting anniversary of the passenger pigeon’s extinction will remind our political leaders of what we have to lose from continued reckless attacks on the ESA. Truly, if there was ever a time to renew our nation’s defining values for conservation, it is on the 100th anniversary of the passenger pigeon’s demise.”
Along with other extinct animals like the mammoth and aurochs, some scientists have nominated the passenger pigeon as a candidate for “de-extinction” through cloning. However, since no intact passenger pigeon DNA exists, portions of rock dove (i.e., “city pigeon”) DNA would have to be substituted, resulting in a hybrid of sorts. Even if it were successfully recreated, it would be very unlikely (read: impossible) that the species would ever regain its historical scope and scale. For that, all we have are the words of those, like Audubon, who chanced upon them at their peak centuries ago:
“Their body is of an elongated oval form, steered by a long well-plumed tail, and propelled by well-set wings, the muscles of which are very large and powerful for the size of the bird.
“When an individual is seen gliding through the woods and close to the observer, it passes like a thought, and on trying to see it again, the eye searches in vain; the bird is gone.”
Citations:
- Schorger, A.W., 1973. The Passenger Pigeon; Its Natural History and Extinction. University of Oklahoma Press, Norman.
- Schorger, A.W. (1955). The Passenger Pigeon: Its Natural History and Extinction. Madison, WI: University of Wisconsin Press. ISBN 1-930665-96-2.
- Bucher, E.H. (1992) The causes of extinction of the passenger pigeon, Current Ornithol. 9, 1–36
- S.L. Pimm, G.J. Russell, J.L. Gittleman and T.M. Brooks, The Future of Biodiversity, Science 269: 347–350 (1995)
- Audubon, J. J. (1832). Ornithological biography (Vol. 1).
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- Schorger, A.W. (1955). The Passenger Pigeon: Its Natural History and Extinction. Madison, WI: University of Wisconsin Press. ISBN 1-930665-96-2.
