A relatively small stretch of swamp between Miami and Naples in south Florida was the only place on Earth where the Florida panther lived 20 years ago. In fact, scientists estimate that only roughly 26 of the animals that once roamed the entire Southeast remained in that swamp, many stunted by genetic defects brought on by inbreeding. In a bid to stave off the same kind of extinction that had wiped out all other mountain lion subspecies (also known as cougars, panthers or pumas) east of the Mississippi, wildlife managers imported eight female cougars from Texas in 1995. It worked. Today, the vigor of the Florida panther is back, according to a new genetic survey published September 23 in Science.

"In the early 1980s and 1990s they were so inbred that they were unhealthy," explains wildlife biologist Dave Onorato of the Florida Fish and Wildlife Conservation Commission, a co-author of the paper. "Genetic restoration has made for a healthier population and population has increased in size since then."

In fact, using samples from 591 individual Florida panthers (Puma concolor coryi) collected since 1981, the scientists traced the bloodlines of the panthers alive today—including the 424 documented panther births since the Texas cougars arrived. The offspring of the original panther population and the imported pumas rapidly grew to as many as 95 adult big cats ranging across Big Cypress National Reserve and other remaining habitats. And this genetic restoration might provide a model for efforts to conserve dwindling big cat populations around the world.

View a slide show of Florida panthers

The scientists also collected their own samples, using houndsmen and their trained bloodhounds (also from Texas) to tree the big cats. But the pumas with Texas lineage proved harder to capture. "The admixed cats, on average, resisted capture more energetically, were more likely not to stay in the first tree that they climbed to avoid the dogs," says geneticist Warren Johnson of the National Cancer Institute's Laboratory of Genomic Diversity in Frederick, Md., lead author of the report.

The population growth, of course, was also helped by the protection of some 120,000 hectares of habitat as well as the construction of highway underpasses to cut down on road kill (10 to 20 pumas are killed every year this way, according to Onorato). But, in a sense, the original inbred population of Florida panthers is now gone, replaced by hybrid descendants with genes from Texas and Florida. Only two females from the "canonical" Florida panther population remain, and the purebred Florida males are less likely to win their battles for territory. "As you become an older fellow your chances of winning a bar fight go down," Onorato says, also noting that Texas and Florida puma populations used to swap genes via ranges that covered the entire Southeast only a century ago.

Territorial battles between pumas are becoming more common as the population rebounds but remains confined to a relatively small habitat. "Finding a way for panthers and people to coexist in Florida—and preserving enough good wilderness for panthers in Florida—that's really what's going to help them the most," Onorato says, noting that it might make sense for the pumas to recolonize central Florida—or even beyond. Johnson adds: "There are many places on the east coast where panthers would flourish, and they eventually may naturally repopulate the region."

But given human demands on the panther's hunting grounds for agriculture and development (and on pumas themselves; hunters killed some 800 pumas a year in Montana alone in the late 1990s), the Florida panther remains imperiled. And that means Florida panthers will likely remain in continual need of imported mates. "Unfortunately, it will have to be done again," Onorato says. "It's just a matter of when."

Or, as ecologist Craig Packer of the University of Minnesota puts it in a commentary on the results also published in Science: "Once the entire planet reaches the same state of economic development and urbanization as the United States, wildlife managers all over the world can look forward to carting rare species from one park to another until the end of time."