Passenger pigeons: Marking a century-old extinction
Sept. 1 marks a sad centenary in our nation’s natural history. In the early days of World War I, a passenger pigeon died alone in her cage at the Cincinnati Zoo. “Martha” had lived her entire life in captivity. She was the last of her kind. The estimated population of passenger pigeons had once been 3 to 5 billion. At the start of the Civil War, they were still one of the most abundant land birds in North America. By the turn of the century, they were extinct in the wild.
The passenger pigeon was a handsome bird, a larger, more colorful version of the ubiquitous mourning dove. They occurred largely east of the Rocky Mountains, nesting in our eastern forests. Nomadic by nature, they moved from place to place based on the availability of beechnuts and acorns – their favorite mast – while also consuming soft fruits such as cherries, berries, plums and grapes, as well as earthworms on occasion. Although they sometimes foraged on agricultural lands, they always returned to the forest to roost and nest. Passenger pigeons routinely flocked together by the tens – or even hundreds – of thousands. A few reliable accounts estimated flocks of more than a million and described streams of birds passing overhead in congregations so large they blocked the sun for days.
Predators had little impact on these vast pigeon colonies, with one crucial exception – man. The birds’ social nature made them vulnerable to commercial hunting. Squab long has been a part of the human diet. We have documentation showing this to be the case in the Piedmont. Bone fragments of passenger pigeons have been unearthed at Town Creek Indian Mound. Early explorer John Lawson wrote about his encounters with the birds near the Sapona village in present-day Davidson County. “[W]e went to shoot pigeons which were so numerous in these parts that you might see many millions in a flock; they sometimes split off the limbs of stout oaks and other trees upon which they roost of nights …You must understand that these birds do not breed amongst us but come down (especially in hard winters) amongst the inhabitants in great flocks.”
The population could withstand this level of hunting, but the species suffered as new technologies evolved to meet the growing demand for squab in the 19th century. Refrigerated railcars allowed for long-distance shipping. Rail lines were built expressly for the purpose of transporting them to burgeoning urban centers. Because of the passenger pigeons’ communal habits, commercial hunters were able to harvest tons of birds at a time. Nestlings were targeted, making it difficult for the population to sustain itself. Once a colony was compromised, the birds stopped reproducing altogether, perhaps hastening their own demise. Like the Carolina parakeet and the ivory-billed woodpecker, the passenger pigeon also declined due to habitat loss, as forests were cleared throughout their range. As with the longleaf pine, the passenger pigeons’ story illustrates the devastating consequences at the intersection of technology, hubris and greed. 
The dramatic loss of this species is mind-boggling, but its rapid extinction must have been even more of a shock to the forest ecosystem. Remarkably, the wild passenger pigeon was never the subject of ornithological research. We’ll never understand the full impact of their loss – their role in dispersing seeds, creating snags, aerating soil, and altering its pH with their droppings. In 1947, the eloquent conservationist Aldo Leopold contemplated this loss. “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.”
Or maybe not. Leopold never imagined that scientists might one day find a way to resurrect the passenger pigeon. Advances in genomic technology have inspired molecular and conservation biologists to study whether it might be possible to tweak the DNA of the genetically similar band-tailed pigeon to bring a species back from extinction. The Carolina parakeet and ivory-billed woodpecker are also on their list of possible candidates. There’s reason to hope our oldest oaks might once again feel the burden of a flock of passenger pigeons.
In the meantime, a diverse group of scientists, teachers, conservationists and artists have started Project Passenger Pigeon (http://passengerpigeon.org/index.html) to raise awareness of this tragic story and use it to promote habitat preservation and species conservation. Time is of the essence as we face “the sixth mass extinction in the 4.5 billion-year history of our planet – one almost entirely driven by human actions.”
The story of the passenger pigeon serves as a cautionary tale for many endangered species, perhaps especially the monarch butterfly. They are similar in terms of sheer numbers and rapid decline. Their colonies, which evolved as a source of protection, also became a vulnerability. While monarchs aren’t a food source, their populations have plummeted in part due to changes in our agricultural practices. If we take the history of the passenger pigeon to heart, we can avoid repeating it.
For more on the passenger pigeon, read Joel Greenberg’s book A Feathered River Across the Sky. To see a video about efforts to “de-extinct” the passenger pigeon, go to http://longnow.org/revive/what-we-do/passenger-pigeon.