There were, at last count, at least five dens with panther kittens this spring in and around Big Cypress National Preserve, which offers arguably the best habitat for the big cats. But how do biologists keep track of these kittens?

Bob DeGross, the preserve's chief of interpretation, explained that a mix of swift examinations and high-tech bar-coding are used to try to follow the fate of newborn kittens.

“We don’t know the exact number of kittens born. The only ones that we know are born are of those females that we have (radio) collared," he said. "We know that that collared female is beginning denning activity when she stops moving on a regular basis and she starts hanging out at a regular spot. It basically means one of two things, either she’s on a kill site from prey, and she’s taking advantage of the available food, or she’s starting to den. Obviously staying on a kill site she might only be there for one, or two or three days. And being on a den she would be there for several weeks.

“Once we identify a female that has started denning behavior, we go out close to the area where we know the den is, and we set up what we call a ‘biologist in a box’. Basically it is a radio receiver hooked to a telephone and so when the female takes off to go hunt ... the 'biologist in a box' will call us and it will let us know that she has left the den site.

“And then we rush into the area where we have a rough idea where the den is from triangulation with the radio signal, and so we rush in and try to find the den while she’s away hunting," Ranger DeGross said. "Then we go in and we basically do run-ups on the kittens, weigh them, we take a skin sample, we take a fur sample, we give them dewormers, and then we also put a little chip in their neck, basically a little rice-sized bar code chip, in their neck, and that’s basically what we do."

Now, while the biologists are working with the kittens, someone else is on the perimeter of the area with a radio receiver. If they detect the mother is returning to the den, "we abandon the site as quickly as possible,” he said.

While regular surveillance of a panther's movements can only be done with radio collars, the tiny bar-code chips implanted in kittens can help biologists learn more about panther biology down the road. When it comes time to replace collars, or collar a new panther, the biologists will scan a captured cat with a bar-code reader to see if it is carrying an implant.

"Typically it is not a panther that we have handled as a kitten. However, this year I think was one of the first years where we actually did capture an adult cat that we had handled and were able to read the bar-code," said Ranger DeGross. "From the bar-code information we knew that it was three years old."

According to wildlife biologists, panther kittens typically remain in the den for about two months. After that period they begin to follow their mother out hunting. They'll usually stay with the mother for about 14 months.

Of the 100-125 Florida panthers thought to be living in and around Big Cypress and Everglades National Park, 28 have radio collars, and 16 of those are females, according to the Florida Fish and Wildlife Conservation Commission. So while there are at least five dens with kittens at last report, there could be many more that biologists are unaware of. And so while these 12-15 wouldn't be enough to off-set the two dozen known panther fatalities in 2009, it's impossible to say whether mortalities are out-stripping reproduction.

"That’s the thing that’s challenging for people. We definitely know every panther typically that is killed by vehicle collisions and things, because they’re reported to us," said Ranger DeGross. "The only kittens that we know are born are those that we handle, those are the ones that are recorded on the website. So I would say that, no, those numbers do not reflect the true birth-death rate.”