One Last Stand

Before Rabinowitz's breakthrough idea of genetic corridors, work on another kind of wildlife corridor had already begun. Nearly 20 years ago, WCS got behind the first biological corridor, connecting rainforest habitats in Mexico and Central America. The idea was to have uninterrupted rainforest from Mexico to the Panama Canal, the large tracts of existing forest joined by forest arteries. It was a beautiful vision—and so ambitious that, though signed into international treaty in 1997, it is still in the process of being carried out to this day.

Rabinowitz's genetic corridor is ambitious in a different way. He formed the idea in 2001, when another set of researchers burst onto an underground genetic railroad already up and running—and didn't realize what they'd found. With new technology for DNA processing, geneticists at the Laboratory of Genomic Diversity in Maryland learned that populations of jaguars from Mexico to Argentina did not constitute different subspecies, as previously thought. "The first thing I did," recalls Rabinowitz, "I ran over and just looked at maps of Central and South America and said, 'What have we been missing?' " The answer was that, in spite of the risks posed by development and poaching, jaguars were still moving through much of their historic range—swimming, at one point, across the Panama Canal—and mixing their genes. Each individual jaguar was a unique combination of genes from the same vast pool.

Unlike biological corridors, genetic corridors are not stretches of untouched habitat. They are compatible with agricultural development, even private ownership of land—but there's a limit to how much development a traveling tiger will tolerate. What people will tolerate is another question, but Rabinowitz believes that resistance to letting tigers or other large wildlife onto developed land is more a matter of intellectual hostility than practical concern. Tigers, like all predators whose livelihoods depend on stealth, prefer to go about unnoticed. Even in tiger habitat, says eminent field biologist George Schaller, "you can go for weeks without seeing a tiger. They don't want contact if they can help it." Rabinowitz's own backyard in New York's Hudson Valley is a thoroughfare for coyotes—a fact he only learned when he set out a camera trap and got a picture of one. The animals' natural discretion is also one reason that mountain lions have made a comeback in California's Hollywood Hills.

A tiger's home range spans up to 800 square kilometers, but a male of "dispersal age"—about two years—will travel up to 1,000 kilometers in search of fresh territory for prey and mates. Only two reserves in the world are currently large enough to accommodate dispersals on this scale—the Hukawng Valley in Burma and Thailand's Western Forest Complex—but neither have the tigers to match their capacity. India, on the other hand, holds more than half of the world's tigers in numerous isolated pockets. Genetic corridors can help populate the large reserves and make small ones more viable. According to statistical models, if just one male tiger per generation—about ten years—makes a successful crossing from one habitat to another—from India to Burma, for instance, or Laos to Vietnam—and adds his genes to a different mix, the entire species gets a new lifeline. (Simply moving tigers from one habitat is quicker, but it almost always backfires: unless you catch a male right at dispersal age, says Rabinowitz, the animal will not accept its new home and try to find its way back. In its confusion, it is also more prone to conflict with humans and livestock.)

Tigers have different names in different parts of the world. India's are the Royal Bengal; in Thailand, conservationists are fighting for the Indochinese. The Siberian tiger looms large in that frigid northeastern tundra, while the Chinese are convinced that the South China tiger is the most beautiful iteration of all. They differ along a spectrum of size, color, and thickness of coat—but with the exception of the Sumatran tiger, which is truly in a genetic class of its own, there is only one tiger species. George Amato, head of genomics research at the American Museum of Natural History, says, "If you walked from southern India to Korea, at no place would you say, 'That [kind of tiger] stopped and this one started.' " The idea behind genetic corridors is not to create artificial gene flows between isolated groups, he says, but to reconstruct "the natural evolutionary path of these animals."

Thirteen countries own a piece of the tiger's natural range. One Panthera corridor would connect several small reserves in the Western Ghats, along the coast of India. Another would run the entire length of the Indonesian island of Sumatra. Between Russia and China, the Siberian tiger has periodically shifted its haunts as populations were hunted or lost their prey. Now some tigers are moving to China again, and Rabinowitz hopes that the story of their return to native soil might overcome the Chinese government's general indifference to wildlife and help legitimize a corridor in the northeast.