Billions of passenger pigeons once darkened the skies above North America. Then, in only a few decades, they became extinct.

Now, a recent collaboration between researchers from Taiwan and the University of Minnesota’s Bell Museum of Natural History marking the 100th anniversary of the species’ extinction can better explain how humans hunted the birds out of existence.

The study highlights why passenger pigeons are still relevant a century after the last of their kind died in captivity at the Cincinnati Zoo on Sept. 1, 1914.

The team of Taiwanese and University researchers found that the species’ population — believed to have peaked between 3 billion and 5 billion — fluctuated dramatically before mass hunting of the bird for commercial purposes took off in the 19th century.

“Usually you think of rare species as being vulnerable to extinction — not super-abundant species,” said Robert Zink, an ecology, evolution and behavior
professor at the University and a researcher for the study.

Though humanity’s role in the passenger pigeon’s demise is well-established, former University graduate student and lead researcher Chih-Ming Hung said he wanted to examine the history of its population to find an additional factor to explain the rapid decline.

Before moving back to Taiwan to work as a postdoctoral associate at the National Taiwan Normal University’s department of life science, Hung extracted dried tissue samples from the toe pads of four preserved passenger pigeon specimens, a majority of which came from the Bell Museum.

Hung and his colleagues were then able to sequence the genomes of three out of the four birds and compare their genetic diversity.

“We realized that if we could get a lot of DNA from passenger pigeons, we could answer the question of whether passenger pigeons have always been super abundant,” said Zink, who serves as the Bell Museum’s curator of ornithology.

Assistant ecology, evolution and behavior professor Keith Barker, who is the current curator of genetic resources at the Bell Museum, said the samples showed less genetic variation than expected, suggesting a natural boom-bust population cycle.

Before humans permanently disrupted the species’ natural life cycle, Hung said, environmental conditions like nesting habits and the availability of food like acorns played a factor in the passenger pigeon’s fluctuating population.

A contemporary lesson

Although popular belief has long held that 19th-century Americans shot the passenger pigeons out of the sky until they vanished, Zink said a combination of commercial hunting, recreational shooting and habitat destruction doomed North America’s once most-common bird.

“All the local predators put together couldn’t put a dent in their numbers,” said Zink, noting that for people at the time, the birds provided a seemingly limitless source of revenue and nutrition.

“This was an era of abundance. No one ever dreamed that you could bring about the extinction of something so common,” he said. “But it turns out, they could.”

Barker said what happened to the passenger pigeon serves as an example of how adverse the results can be when human activity is combined with nature’s unpredictability.

He pointed to the problem of overfishing the world’s oceans as a
contemporary example of how resources that seem to be inexhaustible are not necessarily so.

“We have no idea where the soft spots of these ecosystems are and how far we have to push things before we get catastrophic change,” Barker said.

Hung also cited overfishing as a modern comparison.

“People see marine fish as an unlimited resource,” Hung said. “The consumer [doesn’t] care about how [many] are still there.”

Other birds today face familiar threats like habitat destruction and the looming consequences of climate change, said Mark Martell, the director of bird conservation for nonprofit organization Audubon Minnesota.

“Already we see changes in bird migrations, in bird wintering sites,” Martell said. “Going forward, we’re going to have a real impact on birds, other wildlife and certainly humans.”

For Martell, the passenger pigeon is both a reminder of the harm humans can do and an iconic symbol for conservation. He likened massive flocks that could reportedly take days to fly over a given spot to the buffalo herds that once roamed the Great Plains.

“It was probably an overwhelming sight,” he said, “and something we just won’t ever have again.”