"In 1880, [Montana] was practically uninhabited. One could travel for miles without seeing so much as a traveler's bivouac. Thousands of buffalo darkened the rolling plains. There were deer, elk, wolves and coyotes on every hill and in every ravine and thicket. . . . In the fall of 1883, there was not a buffalo remaining on the range and the antelope, elk, and deer were indeed scarce. . . [T]here were 600,000 head of cattle on the range. The cowboy . . . had become an institution." Granville Stuart, quoted in Donald Worster, Under Western Skies: Nature and History in the American West (New York: Oxford University Press, 1992).

At the close of the 19th century, american bison populations had been obliterated by commercial hunting pressures and deliberate campaigns of extermination. Twenty-five million bison had lived in North America. They were sacred to many Plains Indians, for the Americans they were the living symbol of the "Inexhaustible" natural wealth of America - and they were gone.

Enter William Temple Hornaday, zoologist and taxidermist for what would become the Smithsonian. In the 1880s, Hornaday worked to create a census of the bison and was alarmed to discover "in the United States the extermination of all the large herds of buffalo is already an accomplished fact." Armed with this knowledge, he did the normal, sensible thing: in 1886, he went to Montana to shoot several dozens of the last remaining wild bison for the museum.

In 1889, there were perhaps 600 wild bison in all the world. But as it turns out, that wasn't the end of the bison, or of Hornaday.

The modern idea of conservation* existed in 1880s when Hornaday set out to shoot those bison, but it was the purview of scientific forestry and timber management. Wildlife conservation emerged in America as the product of hunters and sportsman witnessing the decline of the bison and other iconic species of mammals and birds. In 1883, George Bird Grinnell and Teddy Roosevelt were publishing articles in Forest and Stream arguing that the government needed to implement policy to conserve wild game populations for human use (such as ensuring the masculine vitality of the gun-toting American man), and would go on to found the Boone and Crockett Club in 1888 to further that agenda. At the same time, naturalists and environmentalists like John Muir were arguing for the preservation of of "wildness" and natural spaces.

In 1903, Hornaday was now the director of the Bronx Zoo, and with the support of President Roosevelt and other notable figures in the movement, he secured a herd of forty bison for the zoo. In 1905, the first National Parks were established, and the wildlife conservationists won a major victory in restricting hunting and poisoning within the parks (likely saving animals like the bighorn sheep and red wolf from extinction). Hornaday sent 15 bison from the zoo to the Wichita National Forest and Game Preserve to be reintroduced. The 20th century would see the adoption of further law and policy to protect wildlife from over exploitation and habitat loss, culminating (in the US) with the signing of the Endangered Species Act in 1973 which created the framework for species conservation we're still using today.

• An important note: The concept of "preserving an endangered species from extinction" is a product of the modern conservation movement. My answer focuses on that question, but there are other stories that could be told. Generally speaking, indigenous peoples (here I mean people who have lived in and as a part of their local environments for an extremely long period of time) have always understood the potential for human impacts to their environments. The Plains peoples who hunted and relied on bison understood far more about the needs and ecology of the species than the American and European conservationists who undertook to save it - back in Europe, common law and traditional practices for tending the landscape had been relied on for millennia to avoid depleting and destroying precious natural resources. The modern conservationists were a particular sort of men (and they were mostly, though not all, men) acting in a particular time, and with a particular set of values. In between saving the bison from extinction and becoming something of a patron saint to the Boy Scouts, William Hornaday put an enslaved African man on display at the same zoo where he sheltered those bison. His friend and colleague Madison Grant was among the founding fathers of eugenics and scientific racism. They laid the groundwork for some of the most important work in ecology and environmental science today, but we are still grappling with the complexities of that legacy.

I hope this vignette gives you an idea of how early conservation efforts came about. If you want to read more, there is a recently published book on the subject which may interest you: Beloved Beasts: Fighting for Life in an Age of Extinction by Michelle Nijhuis.