John Vaillant is the author of two nonfiction works, “The Golden Spruce” and “The Tiger” and a novel, “The Jaguar’s Children.”

Many years ago, when I was teaching at an elementary school, a student of mine brought a box full of worms to class. He planned to release them at the end of the day, but he forgot about them. I forgot about them too until I returned to the classroom the following morning. What I saw there has stuck with me for nearly 30 years: Somehow the lid had come off the box, and the worms had escaped. Some of them made it only a few feet across the floor, others reached the classroom wall, a few aimed for more distant corners, but they were no match for central heating and wall-to-wall carpet. Every one of them was dead.

Reading William Stolzenburg’s poignant and heroic tale of mountain lions and their epic migrations from an isolated habitat in South Dakota’s Black Hills, I was reminded of those worms. The Black Hills are a small mountain range on the western edge of the Great Plains that is home to a resurgent but embattled population of mountain lions. In 2009, a young tom, crowded out by dominant males, launched himself eastward on a meandering hejira that took him across the plains and through some of the most densely populated areas in the country on a six-state search for a mate. In “Heart of a Lion,” Stolzenburg, a veteran science and wildlife writer, traces this cat’s journey: He confirms its tracks in Wisconsin, camera-trap images in Illinois and DNA samples consistent with Black Hills lions. In so doing, Stolzenburg painstakingly places this intrepid tom in the larger context of mountain lion history and lore and illuminates, through the examples of other wayward males, the hazards of a self-directed rewilding program.

Also known as cougars, pumas and a host of other regional names, mountain lions have more in common with tigers and jaguars than with lions. Unlike their larger, savannah-dwelling namesakes, American mountain lions are primarily forest dwellers. In addition to being able swimmers, they are well-suited to cold climates, but they can live virtually anywhere. Not so long ago, they did — from coast to coast and from the Everglades to the Rockies. As the continent’s dominant carnivore, mountain lions divided their world into marked territories of three or four breeding females overseen by a single tom whose domain might cover hundreds of jealously guarded square miles. Today, only vestiges of these feline kingdoms remain. What Stolzenburg vividly conveys is how profoundly America has changed since lions last had the run of the place.

While indigenous populations found a way to coexist with lions and even revere them, European settlers adopted an “Apocalypse Now” approach, terminating these animals with extreme prejudice rivaled only by their purges of wolves and Indians. By 1910, the mountain lion had been all but extirpated from the lower 48 states, with only handful surviving in Southern cypress swamps. Once one of the largest, most successful and widely distributed predators, the mountain lion had been reduced to a ghost of its former self, haunting only the most remote mountains of the West. But despite being nearly erased from living memory, people keep seeing them, as one researcher put it, like “a UFO with four feet.” In the Eastern states, police and wildlife officials have logged thousands of reports (from hunters, commuters and suburbanites), none of them verified, and most debunked outright as dogs, deer and porcupines. Yet, this former keystone species in North America’s natural order, elusive at the best of times, continues to twang our consciousness like a phantom limb.

"Heart of a Lion: A Lone Cat's Walk Across America" by William Stolzenburg (Bloomsbury )

And now it’s growing back.

From a low point in the 1960s, mountain lions have been reclaiming lost territory, most notably in the West, where their relative success is tied to the hunting and conservation regulations of individual states. The cat’s former strongholds in the Midwest and Eastern states have been far more difficult to recolonize, and this is where Stolzenburg focuses his attention, exploring the region’s natural and human history while also delving into anthropology and paleopsychology. As a result, “Heart of a Lion” is the most comprehensive account of these creatures and their place in our shared present since David Baron’s “Beast in the Garden.” But where Baron built his book around the extremely rare event of a lion attack, Stolzenburg tracks the lions’ far more common and deadly quest for new territory.

Even when itinerant mountain lions survive the great rivers, rail lines and interstates, their success often seems due to dumb luck. After two years and thousands of miles, the lion at the heart of this book was hit and killed by an SUV in Connecticut. Like naive aliens, mountain lions prove themselves strangely inept in manmade landscapes. They walk in traffic and lounge on back porches, and even when they manage to dodge cars and commuter trains, they are sometimes shot by suburban police. Each one of these deaths raises a stark question: How do we accommodate a human-size carnivore that is, on the one hand, charismatic, mysterious and primordially frightening and, on the other, like us in its ambition, entitlement and deep-seated sense of domain?

What becomes painfully clear as Stolzenburg homes in on current attitudes toward mountain lions is that, whether in the Black Hills or Forest Hills, these animals are a hot-button issue as volatile and polarizing as gun control: While many citizens and conservation groups across the country welcome the cat’s return, it’s still open season in Texas , just as it was 100 years ago. In South Dakota, hunting season is also year-round and, this year, 60 lions can be killed in the Black Hills alone. For this New World cat, the world has indeed been made new, but the latest iteration is as unforgiving to them as a classroom is to earthworms.

Heart ofa Lion
A Lone Cat’s Walk Across America

By William Stolzenburg

Bloomsbury. 245 pp. $27