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Male Passenger Pigeon by Tim Hough (Own work) [CC BY-SA 3.0],
via Wikimedia Commons
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Introduction
Parts 1 and 2 provided a history of the most numerous bird species ever known to inhabit North America and the gruesome slaughter of billions of the species, ending with its extinction around the turn of the last century. By the last decade of the 19th century, Passenger Pigeons had all but disappeared from the skies of their normal range in the eastern and mid-western American landscape. People from all walks of life, including the leading ornithologists of the time, had a hard time believing such numbers could vanish, seemingly overnight. But in a few short decades, it became apparent that this was the case.
The End of the Flocks
At first, before the harsh reality of their extinction was known and accepted, it was surmised that the remnants of the great flocks escaped from the genocidal war against them and re-established their flocks in the deserts of Arizona. Or, that they simply moved to South America or Alaska. Rumors persisted that flocks of tens of thousands or simply thousands, and later, hundreds of birds escaped detection in the last remaining virgin forests that were widely scattered throughout the eastern halves of the United States and Canada. These denials of reality enabled those who hunted and trapped these birds to continue pursuing them until every last wild Passenger Pigeon was hunted. This left only the last of the captive, living birds to a few aviculturists with aviaries. By 1900, only three captive flocks, with relatively few specimens, existed. A few zoos had some living birds on exhibit, but after the turn of the century more specimens were in natural history and university museums, some taxidermied into lifelike poses and surrounded by examples of their former habitats.
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Whitman's aviary with passenger pigeons and other species, 1896/98
Hubbard, J. G. - http://www.wisconsinhistory.org/whi/fullRecord.asp?id=53454
Seven passenger pigeons (possibly other types of pigeon as well?), a species of pigeon now extinct. Part of a group of pigeons that lived in captivity in the aviary of Professor C.O. Whitman, professor of Zoology at the University of Chicago.
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Photo from Wikipedia
The last Passenger Pigeon Martha as a mounted specimen.The stuffed skin of Martha in 1921
Shufeldt, Robert W. - Shufeldt, Rober W., Published figures and plates of the extinct passenger pigeon. Scientific monthly, v. 12, no. 5, May 1921, p467. Online: Archive.org
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Martha, The Last Living Passenger Pigeon
Most famous of the few remaining live specimens were George and Martha, a pair housed at the Cincinnati Zoo. This pair represented the last potential breeding pair of Passenger Pigeons in existence and, in fact, became the last two living examples of the species. Consequently, curious humans flocked to the zoo to see the last two living birds. Living in less than ideal conditions in captivity and the endless noise and taunts from the public prevented this last couple from ever breeding. They sat motionless on a perch in a corner of their cage and were unresponsive to the calls, taunts, and shouts of the viewing public to move, turn around, or fly. People would throw dirt and stones at the birds in efforts to have them move and behave in a manner the taunting public wanted to see. By 1910, George died, leaving Martha as the last living example of the species. Then, on a sad day, September 1, 1914, Martha died. Her body was frozen into a 300-pound block of ice and shipped to the national museum, the Smithsonian Institute, where it remains to this day.
The Emergence of Conservation Expansion
With the demise of Martha, the last of the species, concerns about extinction began surfacing in the scientific community. Concern about preventing extinction began to circulate in the scientific community. Today, the questions regarding extinction and the technical challenges and ethics of the de-extinction movement are immense and evolving. Nevertheless, as genetic technology and research races ahead, a scenario that is hard to imagine is becoming harder to dismiss out of hand. In the formative years, this subject of extinction became the source of much heated discussion and eventually led a serious, conservation-oriented movement to emerge and expand. Several organizations, like the Audubon Society, grew from local chapters into a nation-wide network of concerned citizens and scientists. A consensus of opinions believed the best way to deal with the disastrous effects of extinction was to protect potential species and their habitats to insure their survival for future generations and the overall protection of the native American landscape.
 Why Species Should Be Protected
In their classic 1981 book, Extinction: The Causes and Consequences of the Disappearance of Species, Paul and Anne Erlich describe the four major categories of reasons why species should be protected and preserved: (1) other life-forms have a right to exist and ethical decisions should not be based solely on human benefits; (2) other species are aesthetically pleasing and add to human felicity through their beauty and character; (3) other species provide economic, medical, and other “direct benefits” by their continued existence; and (4) extinctions have indirect and long-term effects on ecosystems of which humans are also a part. The Erlichs illustrate this point with the analogy that the “popping of rivets” of an aircraft would eventually render the plane unable to fly.
Personal Thoughts About Loss
Brian Anderson, director of the Illinois Natural History Survey, suggests that extinction be considered in personal terms. Think of the joy on a child’s face as his/her first trout causes the pole to reverberate with the power of the fish felt in the child’s hands. Think of the songbird’s melodious tune as it greets a new sunrise. Think of the sights and smells of nature on a hike through forest, meadow, or riparian habitat that is blanketed with colorful and fragrant wildflowers. Think of the awe and wonder when encountering a bull moose, elk or grizzly in their native habitat. Think of the pleasures associated with eating the bounty of sea life we would ordinarily take for granted – shrimp scampi, lobster drawn in butter, flavorful fish, etc. Now, consider what it might be like to experience the awesomeness of a large flocks of Passenger Pigeons flying low overhead, blocking out sunlight until the flock has flown out of sight.
Thinking De-extinction
We must also question the enormous task of protecting endangered species. Most of the direct answers also apply to why we want to bring back species from extinction. The simplest answers are: to preserve biodiversity, to restore diminished ecosystems, to advance the science of preventing extinctions, and to undo the harm that humans have caused in the past and prevent the same mistakes in the future. Furthermore, the prospect of de-extinction is profound news. This would have been impossible to even contemplate in the past. That something as irreversible and final as extinction might be reversed, is a stunning realization. The imagination soars. Just the thought of Passenger Pigeons alive again (not to mention Dodos, mammoths, Tasmanian Tigers, etc.) invokes the awe and wonder that drives conservation efforts at their deepest level. Species brought back from extinction can and will become the beacons of hope.
How Science Works
Useful science will also emerge. Close examination of the genomes of extinct species can tell us much about what made them vulnerable in the first place. (Most modern extinctions are directly or indirectly the result of human causation). Were they in a bottleneck with too little genetic variability? How were they different from close relatives that did survive? Techniques being developed for de-extinction will also be directly applicable to living species close to extinction. Tiny populations can have their genetic variability restored. A species with a genetic Achilles’ heel might be totally cured with an adjustment introduced through cloning. For instance, a single gene could cause a transmissible cancer. That gene can be silenced in a generation of the species that can be released into the wild. The cancer would disappear in the wild soon after, because the immune species will not transmit it, and species with the immunity will out-reproduce the susceptible until the entire population is immune.
The Emergence of Futurists and Their Organizations
By the twilight of the twentieth century, a new group of scientists and “futurists” began coming together with ideas about restoring extinct species. Research involving genes, DNA extraction, cloning, and other methods were seriously being discussed. One of the earliest personalities instrumental in pursuing the concept of reintroducing extinct species was Stewart Brand, the author and publisher of the wildly popular 1960’s counter-culture guidebook, The Whole Earth Catalog. Now, in the 21st century, he has established the non-profit Long Now Foundation to lead in the de-extinction movement and “provide a counterpoint to today’s accelerating culture and help make long-term thinking more common.” Brand saw reversing extinction as a conservation method of the future. He and his wife, Ryan Phelan, founded the consumer gnomic company DNA Direct, the Long Now Foundation, and the Revive and Restore Project. They chose the iconic Passenger Pigeon for the first de-extinction effort. In January of 2012, he hosted a TED meeting of like-minded individuals and organizations at the Harvard Medical School to discuss various possibilities of bringing back extinct species. Attendees included experts like Beth Shapiro of the University of California, Santa Cruz; David Blockstein of the National Council for Science and the Environment; and renowned Harvard molecular geneticist George Church. A foundation offshoot organization, the Restore and Revive Project, headed by the lead researcher, Ben Novak, is the leading group in the effort to bring back the species. The Restore and Revive Project provides important funding and acts like a “facilitator”, helping to connect geneticists, molecular biologists, synthetic biologists and conservation biologists. Novak is convinced that new technology can bring the Passenger Pigeon back to life. The subject of the Passenger Pigeon first got his attention while he was a university student at Montana State. “I just fell in love with the story of it. This is an absolutely bigger-than-life story of the most abundant bird on the planet going extinct so quickly. This whole idea that extinction is forever is just nonsense. I thought that was too absolute,” he says. A few years later, he began serious research at the Ancient DNA Center of McMaster University in Ontario, Canada.
Modifying Genomes
Novak’s plan, in the simplest terms, comes down to this: sequence the Band-tailed and Passenger Pigeon’s genomes and find the significant differences between them. Edit the DNA from a Band-tailed Pigeon germ cell – the type that develops into sperm or eggs – to match that of the Passenger Pigeon. Implant this cell into the egg of another pigeon, perhaps a Rock Pigeon, which is easy to work with in the lab. Hope that the germ cell will migrate into the gonads of the developing chick. Allow the chick to grow up, and breed two such birds to create a Passenger Pigeon. Teaming up with Beth Shapiro to accomplish this research, they have to figure out which variations correspond to meaningful physical differences. “It’s not impossible,” she said. “It’s just a long time’s worth of work.”
“…a moral obligation…”
Modifying the genome of one species to match that of another would be a big hurdle to cross. Even in humans, mapping traits to genes is a murky discipline. The most promising method comes from Church’s lab, where scientists have developed a technology called Multiplex Automated Genome Engineering that can make fine-scale alterations to bacterial genomes. Novak hopes Church can make similar modifications at crucial points along the Band-tailed Pigeon chromosome. “If I had to bet, I’d say we’ll figure it out. It’s all moving forward at the speed of science,” he said. “It should be possible to reconstruct the entire genome of the Passenger Pigeon,” says Novak. “The species is one of the most promising candidates for reintroducing an extinct species. We caused the extinction of the species. Now we have a moral obligation to bring them back.”
 Passenger Pigeon Project
Revive and Restore has enlisted the support of preeminent scientists and the National Geographic Society to bolster their efforts. Joel Greenberg, a leading researcher for the Field Museum and the Chicago Academy of Sciences Nature Museum, ornithologist, expert on human-caused extinctions, and an author within the group, has created the Passenger Pigeon Project website so interested persons can follow the progress. His book, A Feathered River Across the Sky, documents the history of the species from pre-historic times to extinction.
DNA Sequencing
Novak says the last big step is getting from a strand of Passenger Pigeon DNA to a living bird. He will need specialized germ cells, which scientists know how to extract from chicken embryos, but not pigeons. He is investigating an alternate route to reach the same goal: extracting stem cells from Band-tailed Pigeons instead, and stimulating them to become germ cells. Then they hope to essentially stamp out the divergent sequences from the Band-tailed Pigeon genome and replace them with synthesized Passenger Pigeon genetic material. This has never been accomplished in birds before. Novak remains ever optimistic, thinking a breakthrough will occur in the very near future.
The group created a list of the species that offered the best likelihood of success. They arrived at a list of ten species from around the world, with the North American Passenger Pigeon at the top of the list. The Passenger Pigeon was listed first as it offered the best chances for success. Among the various reasons this species was chosen first are the fact that the DNA could be extracted from hundred-plus-year-old specimens compared to the DNA of animals whose extinction was prehistoric and the DNA from such animal fossils and bones would be very old and degraded compared to the more modern DNA more easily available. Ancient DNA has been broken apart by enzymes and oxygen, zapped with ultraviolet radiation and contaminated by other organisms. “Whenever you touch it, your DNA gets in the sample,” explains evolutionary biologist Beth Shapiro. “If it sits next to other birds in a lab drawer, their DNA gets in the sample.”
Next-generation Sequencing
However, in the last decade or so, a set of techniques known as next-generation sequencing has offered a better way to work with less-than-perfect DNA. The new technology can analyze hundreds of thousands of short fragments (damaged and/or older DNA) at the same time, speeding up the tedious sequencing process and bringing down its cost. In this past decade, sequencing has gotten approximately 500,000 times more efficient, according to biostatistician Steven Salzberg of John Hopkins University.
Using next-generation sequencing, scientists have discovered that the DNA of our modern-day Band-tailed Pigeons is nearly identical to that of the closely related Passenger Pigeon. This was an important step. The short, mangled DNA fragments from museum specimens do not overlap enough for a computer to reassemble them, but the modern Band-tailed Pigeon genome could serve as a scaffold. Mapping Passenger Pigeon fragments onto the Band-tailed sequence would suggest their original order.
Therefore, scientifically, this is a more doable project with smaller budgets and quicker time frames. However, some practical questions arise when we consider bringing back this species from extinction.
Potential Problems from De-extinction
For example, Passenger Pigeons thrived best when they flocked in the largest numbers possible. Before the settlement and development of the larger North American land mass, there existed enough habitats to support flocks composed of millions, hundreds of millions and even billions of birds. Society today would not put up with such large number of birds that would blot out the daytime sunshine and leave a virtual carpet of pigeon guano. When the country was young and agriculture was the basis of the economy, the guano provided excellent and cheap fertilizer. Farmers appreciated the major influx of highly regarded natural fertilizer that improved farming conditions and increased the value of the farmland. However, today, such large flocks necessary for survival would not be appreciated or tolerated. In addition, the continent no longer is blanketed in nut-producing forests that provided the birds with everything they needed to thrive – trees that provide food, shelter, roosting, and breeding opportunities.
Those factors alone lead to further questions that must be addressed. How many decades of crossbreeding would be necessary? Is it worth the time, money and energy necessary for the project to succeed in order to be considered a success? At what point, if ever, does a genetically altered Band-tailed Pigeon become a Passenger Pigeon? If the immense flocks that this species needs for best survival cannot be duplicated in today’s limited habitat and range, is it worth doing if only a relatively few of these birds are doomed to a non-natural existence in zoos? In addition to these important questions about creating large, wild, reproducing flocks, a host of other political, scientific, and social questions remain and new questions will arise that could present insurmountable challenges in the future. In any case, the genetic research continues and, hopefully, answers will present themselves along the way.
Keystones and Rewilding
Some extinct species were important “keystones” in their home regions. Restoring those species would help our current conservation efforts in preserving our ecological richness and biodiversity. The Passenger Pigeon was a keystone species for the whole of the eastern deciduous forests, from the Mississippi to the Atlantic Ocean, from the Deep South clear up into Canada. Restoring keystone species can also serve as icons, inspiring the protection of a whole region. These types of efforts can bolster the fledgling “rewilding” movements that are occurring in Europe and across the globe, connecting tracts of abandoned farmlands into wildlife corridors spanning national boundaries and insuring suitable habitat for future generations.
Future Potential
Similar projects to establish “wildways” joined across American eastern states and Canada could benefit from the idea of making the region ready for Passenger Pigeon flocks, as well as the beautiful Carolina Parakeet, once the most colorful bird in the eastern region of the continent and overlapping much of the original range of the pigeons. If the initial projects prove to have merit and become successful, perhaps our children will be able to experience Ivory-billed Woodpeckers, Labrador Ducks, and a host of other birds that have become extinct. Prehistoric extinctions were largely caused by natural phenomena such as ice ages, volcanic eruptions with worldwide repercussions, extreme climatic conditions, predation, asteroids colliding with the planet, etc. Because humans played an important role in the modern extinction of whole species, perhaps resurrecting species is in order. And perhaps, a bit of redemption might come with it.
Further Reading
Much has been written about the Passenger Pigeon, its natural history and the story of its rapid extinction. If this three-part article has whetted your appetite to learn more, I have listed several source materials worth reading.
A Feathered River Across The Sky, Joel Greenberg, Bloomsbury, 2014
The Mammoth Cometh, Nathaniel Rich, The New York Times Magazine, February 27, 2014
The Plan To Bring The Iconic Passenger Pigeon Back From Extinction, Wired Magazine, March, 1023,
Say We Really Do Bring The Passenger Pigeon Back From Extinction – Then What?, Greg Miller, Wired Magazine, March 26, 2013
The Second Cooing: Raising Passenger Pigeons From The Dead, Philip Bethge, (English Edition) Der Spiegel Magazine (Germany), April 12, 2013
Century After Extinction, Passenger Pigeons Remain Iconic – And Scientists Hope to Bring Them Back, Carl Zimmer, National Geographic Magazine, August 30, 2014
Opinion: The Case For Reviving Extinct Species, Stewart Brand, National Geographic News, March 12, 2013
Gone Forever: A Contemporary Look at the Extinction of the Passenger Pigeon, David Blockstein, American Birds 39, Winter 1985
The Passenger Pigeon: A Study in the Ecology of Extinction, I.L. Brisbin, Modern Game Breeding 4, 1968
The Wild Pigeon at Englewood, New Jersey, Frank Chapman, Auk 13, 1896
The Passenger Pigeon – Only One Pair Left, Ruthven Deane, Auk 26, 1909
Potential Effects of Passenger Pigeon Flocks on the Structure and Composition of Presettlement Forests of Eastern North America, Joshua Ellsworth and Brenda McComb, Conservation Biology, December, 2013
The Passing of the Passenger Pigeon, Ludlow Griscom, American Scholar 15, 1946
Human-Wildlife Competition and the Passenger Pigeon: Population Growth from System Destablization, Thomas Neumann, Human Ecology 13, 1985
The Last Passenger Pigeon, Gene Stratton-Porter (edited by Bill McGibben), American Earth, 2008
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Passenger pigeon shoot by Smith Bennett[2] [Public domain], via Wikimedia Commons
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