Of all the big cats, the most magnificent and formidable is the Amur tiger. An adult male may weigh more than five hundred pounds and measure eleven feet from nose to tail. These prodigious beasts inhabit not the tropical jungles of India and Southeast Asia, home to most of the world’s tigers, but the snow-swept forests of Russia’s far east, where the Amur River borders northeast China. In winter their coats may thicken and pale to a ghostly version of their summer ones, blending with the snowscape. They are so elusive that even humans living within their territory may go all their lives without glimpsing more than a trail of pugmarks in the snow. But their presence haunts Russian villagers. Tales of their sudden appearance abound, and those who have seen them never forget.

Until recently much of the tigers’ behavior was unknown. With the melting of their tracks each spring, their movements became nearly impossible to trace.…