In 1958 Florida panthers (Puma concolor coryi) were put on the state endangered species list. By 1967 panther populations dwindled to less than 50 and the cats were also put on the federal endangered species list. Many of the dangers to panthers resulted from humans encroaching on their habitat. Shrinking territory led to panther deaths, smaller populations, inbreeding, genetic defects and higher mortality.
Scientists and politicians took measures to protect the cats. To stop them from being killed on highways, fences and underpasses were built for them. The federal government reclaimed about 25,000 acres for wildlife preservation, and the state reclaimed about 70,000 acres. But even this was insufficient, as one male panther can require hundreds of square miles of territory.
Various plans to revive the panthers proved futile and all were highly controversial. It seemed like a far-fetched and disparate suggestion when some scientists suggested taking them out of the wild and breeding them in zoos. A St. Petersbug Times article from March 21, 1993; "Cat Fight", documented some of the politics surrounding the scheme. The "Fund For Animals", claimed it was futile to raise panthers in captivity without assuring that they had adequate habitat. Some environmentalists disagreed and thought captivity was the only way to save the animals. State and federal agencies thought the captivity programs were too severe. To and fro they argued, year after year while various conservation efforts sputtered and failed.
Finally a plan was hatched to try to introduce other animals of a different subspecies into the region. Biologists conducted a trial run in 1988 when Texas cougars (Puma concolor stanleyana) were brought to different reserves in Florida to see if they would survive. The cougars barely made it. Some were killed, others wandered onto farms looking for food, and some had to be removed and brought back to Texas. The biologists persisted. They brought more cougars into Florida in 1993 according to an article in the New York Times (May 11, 1993); "Cougars enlisted in Effort to Save the Florida Panther". This time they imported younger animals, and introduced them to their new habitat after hunting season, so that they would be more established before being displaced by dogs. Females were brought in instead of males because they required less habitat. Throughout 1993 and 1994 according to various news sources, animals were brought from Texas, radio labeled, tracked, and removed if they became problematic. Another article in the NYT (November 2, 1999) reported that the introduced panthers had produced quite a few "hybrid" cubs; "Texas Rescue Squad Comes to Aid of Florida Panther".
Throughout the years, as they were shot, killed by traffic or removed after homeowners complained, the program at times seemed be destined for failure, either logistical or by lobbying efforts against the experiment. Scientists expressed disapproval. The panthers were doomed without more territory said some, while others insisted that native populations were stable and/or growing, that territory had shrunk and could only support a small population, or that the panthers were "specialized", and would never populate a wider territory. More complained that biodiversity efforts and budget were being wasted on the program or that the hybrid offspring would lose the endangered status of the purebreds.
However it seems like the program is actually working. Pimm et al recently publicized a research paper forthcoming in Animal Conservation (2006); "The Genetic Rescue of the Florida Panther", which challenges some of the opposing beliefs. They show that hybrid panthers have successfully moved into new territory. The authors acknowledge the implausibility of their numbers (3 times more hybrids surviving then purebreds), but nevertheless say that the hybrid cubs appear to be heartier than the indigenous populations. Females hybrids survive longer then purebred panthers but males don't. While their study offers support for this type of population survival intervention, the authors don't jump to conclusions about the success of such genetic introductions. Rather they acknowledge that it's a complicated issue and that arguments on both sides are "logically compelling". According to the Duke University press release
"Pimm was himself skeptical about the success of such a rescue attempt in his 1991 book, "The Balance of Nature? Ecological issues in the conservation of species and communities." He acknowledged in his interview and in the new paper that 'I was wrong.'"
As the re-population efforts progress, another thing that is brought into question is the notion of a separate "Florida panther" species. In the popular press, press, most accounts now refer to both subspecies as "panthers" rather then drawing a distinction between the Florida cats as "panthers", and the Texas cats as "cougars". That terminology based on dubious territory distinctions led to people to believe in the rather special species of Florida panthers versus the "common" cougars. Although there are genetic distinctions between the cats, scientists like Dr. Stephen O'Brien showed that the cougars range historically extended throughout America, and that the popularly referred cougars, panthers, jaguar, puma...were subspecies that shared descendants.
[More on the Florida Panther:] PloS Biology Has an article on conservation efforts of the Panther here