The first time Ben Novak saw a passenger pigeon, he fell to his knees and remained in that position, speechless, for 20 minutes. He was 16. At 13, Novak vowed to devote his life to resurrecting extinct animals. At 14, he saw a photograph of a passenger pigeon in an Audubon Society book and “fell in love.” But he didn’t know that the Science Museum of Minnesota, which he was then visiting with a summer program for North Dakotan high-school students, had them in their collection, so he was shocked when he came across a cabinet containing two stuffed pigeons, a male and a female, mounted in lifelike poses. He was overcome by awe, sadness and the birds’ physical beauty: their bright auburn breasts, slate-gray backs and the dusting of iridescence around their napes that, depending on the light and angle, appeared purple, fuchsia or green. Before his chaperones dragged him out of the room, Novak snapped a photograph with his disposable camera. The flash was too strong, however, and when the film was processed several weeks later, he was haunted to discover that the photograph hadn’t developed. It was blank, just a flash of white light.

In the decade since, Novak has visited 339 passenger pigeons — at the Burke Museum in Seattle, the Carnegie Museum of Natural History in Pittsburgh, the American Museum of Natural History in New York and Harvard’s Ornithology Department, which has 145 specimens, including eight pigeon corpses preserved in jars of ethanol, 31 eggs and a partly albino pigeon. There are 1,532 passenger-pigeon specimens left on Earth. On Sept. 1, 1914, Martha, the last captive passenger pigeon, died at the Cincinnati Zoo. She outlasted George, the penultimate survivor of her species and her only companion, by four years. As news spread of her species’ imminent extinction, Martha became a minor tourist attraction. In her final years, whether depressed or just old, she barely moved. Underwhelmed zoo visitors threw fistfuls of sand at her to elicit a reaction. When she finally died, her body was taken to the Cincinnati Ice Company, frozen in a 300-pound ice cube and shipped by train to the Smithsonian Institution, where she was stuffed and mounted and visited, 99 years later, by Ben Novak.

The fact that we can pinpoint the death of the last known passenger pigeon is one of many peculiarities that distinguish the species. Many thousands of species go extinct every year, but we tend to be unaware of their passing, because we’re unaware of the existence of most species. The passenger pigeon’s decline was impossible to ignore, because as recently as the 1880s, it was the most populous vertebrate in North America. It made up as much as 40 percent of the continent’s bird population. In “A Feathered River Across the Sky,” Joel Greenberg suggests that the species’ population “may have exceeded that of every other bird on earth.” In 1860, a naturalist observed a single flock that he estimated to contain 3,717,120,000 pigeons. By comparison, there are currently 260 million rock pigeons in existence. A single passenger-pigeon nesting ground once occupied an area as large as 850 square miles, or 37 Manhattans.

The species’ incredible abundance was an enticement to mass slaughter. The birds were hunted for their meat, which was sold by the ton (at the higher end of the market, Delmonico’s served pigeon cutlets); for their oil and feathers; and for sport. Even so, their rapid decline — from approximately five billion to extinction within a few decades — baffled most Americans. Science magazine published an article claiming that the birds had all fled to the Arizona desert. Others hypothesized that the pigeons had taken refuge in the Chilean pine forests or somewhere east of Puget Sound or in Australia. Another theory held that every passenger pigeon had joined a single megaflock and disappeared into the Bermuda Triangle.