BRISTOL, R.I. — This year marks the centenary of the extinction of the passenger pigeon — once one of the most abundant bird species in the world. In the mid-1800s, billions of passenger pigeons would darken the North American skies. In 1866, one flock in southern Ontario was reported as being a mile wide and 300 miles long; it took 14 hours to pass overhead and included some 3 billion birds.

By the beginning of the 20th century, however, passenger pigeons no longer lived in the wild. The last one of its kind, a female named Martha, died in captivity at the Cincinnati Zoo on Sept. 1, 1914. Her time there was hardly glamorous.

“People threw sand at her to get her to move,” said Joel Greenberg, a research associate of the Chicago Academy of Sciences Peggy Notebaert Nature Museum and the Field Museum, during a talk last month at the Audubon Society’s Environmental Education Center. “She never knew long flight.”

Her carcass was frozen into a block of ice and sent to the Smithsonian in Washington, D.C. The taxidermic Martha isn’t currently on display.

Greenberg, the author of “A Feathered River Across the Sky: The Passenger Pigeon’s Flight to Extinction,” said the species’ extinction is a “grand and tragic tale.”

“The passenger pigeon is gone because of man,” he said. “The birds were a cheap food supply, selling for pennies apiece. There was a class of worker who chased the birds year-round, from the Atlantic coast to the Great Plains. These birds knew no rest.”

Ultimately, the commercial exploitation of pigeon meat on a massive scale and the loss of habitat wiped the species out. By what method were they killed? Passenger pigeons were clubbed to death or caught in huge nets. The woods where flocks roosted were often burned, the charred bodies then picked up off the ground.

Shooting, however, was the preferred killing method, according to Greenberg. He said hunters sewed the eyelids shut of live passenger pigeons and fastened them to stools — hence the phrase “stool pigeon” — to lure traveling flocks.

In the mid- to late-19th century, shooting matches didn’t feature clay pigeons. Greenberg said during three-day tournaments up to 40,000 passenger pigeons could be shot and killed.

“The story of how the most abundant bird in North America disappeared so quickly is unique in the annals of human history,” according to the Project Passenger Pigeon website. “Though a century has passed since the loss of this species, it remains a poignant example of nature’s abundance, as well as a powerful reminder of humanity’s ability to exhaust seemingly endless riches.”

The last wild passenger pigeon was shot and killed on April 3, 1902 in Indiana, according to Greenberg. “Hunters knew the number of birds was dwindling, but instead of laying off, they wanted to kill every last one before they died off on their own,” he said.

Project Passenger Pigeon is an international effort of 160 member institutions, including six in Massachusetts and three in Rhode Island, to commemorate this year’s anniversary and use it to raise awareness of current issues related to human-caused extinction, explore connections between humans and the natural world, and inspire people to become more involved in building a sustainable relationship with other species.

“The depleting of wildlife in the 19th century led to a great movement in the 20th century to protect it,” Greenberg said.

The Endangered Species Act of 1973 was the 20th century’s signature effort. It was designed to “protect critically imperiled species from extinction as a consequence of economic growth and development untempered by adequate concern and conservation.”

Now, 40 years later, critics want to gut the one of the nation’s cornerstone environmental laws. In February, 13 House Republicans called for an overhaul of the act. In a 64-page report, the study group’s members say they want to curtail litigation from wildlife advocates that has resulted in protections for some species, and to give states more authority over imperiled species that fall within their borders. The report also recommends increased scientific transparency, more accurate economic impact studies and safeguards for private landowners.

The report claims only 2 percent of protected species have been recovered despite billions of dollars in federal and state spending. Throughout its four-decade history, the law has faced criticism from special interest groups and lawmakers, who have argued actions taken to shield at-risk species such as the northern spotted owl and the greater sage-grouse have severely hampered economic growth.

Proponents of the federal law, such as Greenberg, Sen. Sheldon Whitehouse, D-R.I., and Project Passenger Pigeon, credit the act with staving off extinction for hundreds of species, from the American alligator to the bald eagle. They note the act’s 120 success stories and point to a growing number of plants and animals worldwide in steep decline, such as the whale shark and the little brown bat.

“We need to be vigilant and block attempts to gut the Endangered Species Act,” Greenberg said. “Our oceans are being depleted at record numbers. People still shoot whopping cranes.”

Of the world’s 15 species of cranes, 11 are considered threatened or endangered. Among these, the rare whooping crane found only in North America, has been successfully bred from a low of 21 birds in the 1940s to almost 600 in 2011, according to Project Passenger Pigeon.

The organization also noted that by mid-century, the United States may witness the extinction of 25 percent of its native plant species, with equal or greater losses expected for plant species worldwide.

Greenberg said government can’t be allowed to become apathetic to protecting the environment from development pressures and humanity’s well-documented shortsightedness. As an example, he noted the 1897 law passed in Michigan that banned all killing of passenger pigeons. Of course, by then only a handful still existed in the wild — anywhere.

“New England’s coasts are home to North Atlantic right whales, which migrate along our coastline, as do humpback and fin whales. Hawksbill, Kemp’s ridley and leatherback sea turtles can be spotted in the summer,” Whitehouse wrote in an op-ed published by ecoRI News last year. “Piping plovers seek refuge on our shores. These iconic creatures of our region are afforded special protections under the Endangered Species Act.”

Editor’s note: According to Project Passenger Pigeon, the last recorded sightings of passenger pigeons in Rhode Island are as follows: Walter Angell collected a specimen in Cranston on Nov. 2, 1886; T.M. Flanagan is said to have obtained up to 12 birds in Warwick in the same year or the year before; a flock of eight was reportedly seen by the same Walter Angell in August 1893. In Massachusetts, several were seen in the early 1890s at Walnut Hill in Medford, and in North Reading, Plymouth and Woods Hole; the last specimen was shot in Melrose on April 12, 1894. According to Greenberg, there are about 2,000 stuffed passenger pigeons in collections worldwide.