“Tiger Tiger,” a documentary from director George Butler, won the inaugural William W. Warner Beautiful Swimmers Award, which recognizes work with a “spirit of reverence for the natural world.” (White Mountain Films Production)

In one of the first shots of “Tiger Tiger,” we see the film’s subject, wildlife biologist Alan Rabinowitz, grunting his way through a daily workout, including punishing biceps curls.

For fans of “Tiger Tiger’s” director, George Butler, that moment is sure to elicit a knowing smile. Butler, 70, has made several wildlife and conservation films over a nearly 40-year career. But he is and probably always will be best known for his feature debut, a 1977 documentary featuring a telegenic Austrian weight lifter named Arnold Schwarzenegger.

In an e-mail interview, Butler allowed that bodybuilding is a subject “I know quite a lot about.” But the scene in “Tiger Tiger” — which plays Thursday night as part of the Environmental Film Festival — isn’t meant as a wink. “Alan is a fitness fanatic,” Butler explained, “and the scenes of him working out show his strength of character, with his constant battle to maintain his fitness and his health. The scene of him ‘pumping iron’ . . . dramatically introduces his passion and commitment to his work.”

Rabinowitz, who speaks in a cadence more akin to a cop or a prizefighter and who has been researching big cats for more than 30 years, is indeed a magnetic figure, as fascinating and sympathetic as the “charismatic mega-fauna” he has devoted a lifetime to studying. As the chief executive of the conservation nonprofit Panthera, he has traversed most of the geographic area known as “Tiger Range,” where the globe’s endangered tigers still roam freely and reproduce. But Rabinowitz had never ventured to the Sundarbans, a vast, forbidding mangrove forest on the border between India and Bangladesh. Having heard rumors that between 300 and 400 semi-aquatic Royal Bengal tigers were living there, Rabinowitz was skeptical but intrigued. And he overcame an even deeper skepticism regarding documentaries to allow Butler and his team to tag along.

“Frankly, by the time I met George I’d had it with documentaries,” Rabinowitz recalled. “I had too much on my plate to do documentaries and, to be quite honest with you, I don’t feel that the standard documentary changes anything out there.”

But Rabinowitz was won over — and not just because he’d been a huge fan of “Pumping Iron” and its sequel, “Pumping Iron II.” “George impressed me,” he said, adding that he watched Butler’s past films, including “In the Blood,” about a historic African safari; “The Endurance,” about the Shackleton expedition to Antarctica; and “The Lord God Bird,” about the rare ivory-billed woodpecker. “I could see that he was different,” Rabinowitz said. “He saw things a different way, he wasn’t selling out. . . . And in my case he truly wanted to help tigers. He wanted to make something that could be used as a means of moving people and bringing them into the conservation scheme, and I was impressed by that. And I continued to be impressed by him on our trip in the Sundarbans.”

“Tiger Tiger” puts viewers right in the boat as Rabinowitz and Butler visit the Indian side of the Sundarbans — where the tiger population coexists relatively well with human inhabitants, and their habitat is carefully monitored — and then the Bangladeshi side, where the animals’ situation is far less secure. In many ways, “Tiger Tiger” is a political film, demonstrating what it takes for an idea — in this case, preserving the tiger population — to take root in a community for which that idea is economic and even existential anathema. But by far the most mesmerizing sequences of the film star the animals themselves, especially when they’re seen in candid, close-up footage captured by the cameras Rabinowitz uses to track the tiger population.

There are moments — when an animal solemnly gazes into the camera as the audience gazes back, or when Rabinowitz patiently listens to villagers express their fears and frustrations with the tigers who threaten their lives and livelihoods — when “Tiger Tiger” seems to capture less a social or even environmental story than a spiritual one. It was just that mystical element that led Environmental Film Festival founder and director Flo Stone to present it with the inaugural William W. Warner Beautiful Swimmers Award, established by the family of the late author with the mandate to recognize work with a “spirit of reverence for the natural world.” (The award is named for Warner’s Pulitzer Prize-winning book, “Beautiful Swimmers,” about the Chesapeake Bay’s blue crab population.) For Stone, Butler’s film “was just heaven-sent, because it’s such a magnificent film, and beautifully reflects that wish.”

Then there are the life-and-death stakes of “Tiger Tiger” — not only for the graceful, nearly extinct creatures at its center, but also for Butler’s own trek through an area “populated by man-eating tigers, saltwater crocodiles, cobras and kraits, sharks, and any number of other poisonous creatures” and Rabinowitz’s battle with leukemia, which for Butler added a layer of poignant resonance. “It’s a compelling story,” the filmmaker said, “a dying man trying to save a dying species.” Viewers will be gratified to know that Rabinowitz is doing well, and still working. “My white-blood-cell count is up a little bit, and I’m somewhat immuno­compromised,” he said, “but other than that, I’m living my life as normal — which is beyond normal.”

“Tiger Tiger” (90 minutes) will be shown at 7 p.m. at the Carnegie Institution for Science’s Elihu Root Auditorium, 1530 P St. NW. George Butler and Alan Rabinowitz will answer questions after the screening. The screening is sold out, but rush tickets may become available. For more information, visit www.dcenvironmentalfilmfest.org.