What Is Preying on Florida’s Panthers? : Sexuality: Some researchers blame pesticides for the big cats’ plight. Others cite development and inbreeding. With only 30 to 50 left, the fate of the species lies in the balance.

Just past dawn, Florida Panther No. 52 is on the run, the beep from her radio collar growing steadily louder.

From the window of a Cessna, state biologist Darrell Land points out a spot, and the pilot spirals down, hovering above an emerald carpet of pines and palms. The sleek, tawny-colored cat is crouched below, checking out a herd of deer for breakfast.

“I’ll be damned!” Land said, checking the panther through his binoculars. “That’s the first one I’ve seen in months.”

Three mornings a week, Land takes to the air to track these rare, nocturnal felines using radio signals, scribbling each cat’s location and identification number on a green topographical map spread across his lap. Only 30 to 50 Florida panthers remain, making them one of the nation’s most troubled endangered species.

For years, wildlife biologists have presumed that the big cats are vanishing because the marshy forests surrounding the Everglades have been chewed up by South Florida’s sprawling farms and suburbs. With so little space to roam, they inbreed, passing on reproductive defects such as low sperm counts.

But now biologists are wondering if another factor also has been playing a key role--chemicals that imitate hormones and feminize animals.

A scientific debate over the felines--whose protection is a highly contentious subject in Florida--has erupted between those who believe that pesticides are at fault and those who blame development and inbreeding. At stake in this argument is the fate of the species.

“My argument is contaminants and theirs is inbreeding,” said Charles Facemire, a U.S. Fish and Wildlife Service contaminants specialist. “I believe these animals have been feminized. I have no proof. I may be dead wrong, but if I am, I will really be surprised.”

Male panthers may have abnormal estrogen levels--higher in some cases than many females. About 90% have large percentages of dead sperm, and more than half suffer from cryptorchidism--in which one or both testes fail to descend.

“All of those things have been shown to be caused by environmental estrogens or other endocrine-disrupting chemicals in other animals,” Facemire said. “Every one of them.”

But Michael Dunbar, wildlife research veterinarian for the Florida Game and Freshwater Fish Commission, disagrees.

“There is no data in panthers supporting any of that, so I am very pessimistic that we have a problem as far as estrogenic chemicals having effects,” he said. “It is worth investigating, but people just have to use common sense about it. From what I see in the animals I am working with, it doesn’t seem to be a problem.”

A year ago, Dunbar compared panthers with abnormal testicles to normal ones and found no correlation to their hormones. Both had high estrogen, so Dunbar suspects that is normal in panthers compared to other large cats.

“If (environmental hormones) were a problem, we would be seeing more symptoms in many species there,” Dunbar said. Raccoons, bobcats, deer and bear seem to have no similar sexual problems.

Facemire, however, said Florida officials are wedded to the inbreeding theory because it is easier to fix. The state wildlife agency is planning to import cougars from Texas to mate with Florida panthers and increase the gene pool. But those cats could be doomed to sire abnormal offspring, too, if Facemire’s theory is correct.

If the panthers’ problems are caused by estrogenic chemicals, a massive investigation and cleanup of pesticides and other contamination would have to be conducted in the Everglades and surrounding areas.

“These are highly charged, highly controversial issues,” Facemire said. “Someone has to pay if we prove it’s contaminants.”

Although panthers roam the heart of a sugar and citrus belt, no one has tested the cats--or the raccoons and deer they feed on--for hormone-disrupting chemicals. DDT and other pesticides pollute nearby canals.

University of Florida wildlife endocrinologist Tim Gross said the most likely explanation is a combination of the two. “More than likely it’s a pollution problem” behind the sperm abnormalities, while inbreeding probably causes the cryptorchidism, Gross said.

Land, however, is dubious that the sperm and testes disorders are even posing a problem in terms of births. He believes the panthers are recovering, based on the number of kittens he sees.

But the new generation of kittens could be infertile if pollution-caused problems have been passed from their parents. The true test will come when the young males are old enough to mate.