In 1995, separate pairs of Texas female panthers fitted with radio collars were released in each of the four sections of South Florida where Florida panthers were known to be living, the authors wrote. Five of these eight cats are known to have produced hybrid kittens. By 2003, all three of the surviving Texas adults had been removed from the wilds, since wildlife managers "wanted to keep outside genetic exposure to a minimum," Pimm said.
Beginning in 1992, researchers also briefly captured kittens and inserted microchips into them to track their whereabouts and fates. Of the 118 purebred and 54 hybrid kittens that received microchips, 13 purebred and 20 hybrids survived long enough to also receive adult radio collars, according to the paper.
The researchers followed how well the kittens born to purebreds survived and compared them to the hybrids -- those that had Texas mothers or grandmothers. "More than three times as many hybrid kittens appear to reach adulthood as do purebred ones," the authors wrote.
According to Pimm, native Florida panthers were "becoming famous" for an array of genetic abnormalities, including low sperm counts and heart defects. "It turns out that purebred kittens don't survive very well," he said. "They die in very high numbers. Once you get new blood, those defects disappear from the population. Hybrids are better than inbred animals."
The paper also notes that "hybrid cats are beginning to expand their ranges to areas previously thought to be unsuitable," meaning environments "once supposed to be unable to support them."
Purebred Florida panthers have been confined largely to protected areas north of interstate 75 and west of State Highway 29. "I think they were surviving in this area because they had the least trouble there," Pimm said. In contrast, hybrid offspring have been moving successfully south and east into new sections of the Everglades Nationa