Editor's note: This updates with additional details from preserve officials, including efforts to save the den from the wildfire and the location of the den.

Neither efforts by crews to remove brushy fuels nor water drops from helicopters could save a litter of four Florida panther kittens from dying in a wildfire sweeping Big Cypress National Preserve.

"We tried everything that we could and unfortunately for safety reasons we had to move out of the area," Bob DeGross, the preserve's chief of interpretation, said Wednesday afternoon.

The deaths this week brought to at least 16 the number of panthers that have died since the beginning of the year. One was shot in a rural area of Seminole County, far north of the preserve in central Florida, back in March.

Portions of Big Cypress have been burning since late April, when a lightning strike ignited brush in the preserve. The fire, nicknamed "Jarhead," was touched off April 26. At last count it covered nearly 16,500 acres and was being fought by 220 personnel.

“It was actually three lightning strikes," said Mr. DeGross, who said the preserve and surrounding countryside have been locked in one of the longest droughts in memory. “As far as I know, this is one of the worst droughts that we’ve seen for the last 30 years or so. And I think some people even said as much as 50 years.”

Wildlife biologists knew the fire was approaching the den because they had given the five-week-old kittens a checkup shortly after they were born and knew where the den was.

"We were aware of it and we were doing everything that we could within our power to protect the den site as much as possible," said Mr. DeGross. "That entailed everything from trying to minimize the heavy vegetation. Panthers in Florida, they den in some of the heaviest vegetation. They den in pine/saw palmetto type of cover, and saw palmetto and pine forest is very susceptible to fire."

That thick undercover made it extremely difficult to protect the kittens from the flames, the park official said.

"We were trying to do suppression around it in terms of making sure the fuels were reduced and things like that, and then as the fire was approaching we were actually doing water drops around it via helicopter, trying to increase the moisture level in the vegetation around the den," said Mr. DeGross. "And it got to a point where the smoke was so dangerous that the helicopter had to move out of the area because it was putting staff safety at risk.”

Mr. DeGross said the den was located in the Turner River Unit of the preserve. Two privately owned hunting camps also were lost to the flames, he said.

Whether other panther litters were in danger from the wildfire was impossible to say.

“This is the only den that we know about, and again the only reason that we know about it is because of the fact that we were monitoring the den," Mr.DeGross said. "I’m sure there are other cats and possible dens that are associated with the fire.

"The likelihood of an adult cat being lost because of a fire is probably fairly slim," the official added. "But in terms of the dens, some of them might be older where the kittens actually could be able to follow the mother. Some of them might be younger where the mother is actually able to move the kittens.

"It’s my understanding that this particular den site, this particular den group, was just at that age where they were a little bit too old for the mother to move them efficienctly, and they were a little bit too young to follow the mother.”

Meanwhile, an investigation is ongoing in Seminole County in connection with the shooting of a panther. While some leads have been received on a hotline -- 888-404-3922 -- set up for information leading to the arrest and conviction of the individual who shot and killed the panther back in March, there have been no arrests in the case, said Mr. Warren.

A $5,000 reward has been posted by the Fish and Wildlife Service, the Florida Fish and Wildlife Conservation Commission, and the Human Society of the United States for information that leads to a successful conviction of those responsible.

While at least 16 panthers have died or been killed this year in south Florida, there have been reports of only 15 having been born this year, according to state wildlife officials, and four of those died in the wildfire.

There are only about 100-160 adult Florida panthers left in Florida, according to the Fish and Wildlife Service. The Florida panther is protected under the Endangered Species Act of 1973, which currently lists the species as "endangered." This means the Florida panther is in danger of extinction throughout all or a significant portion of its range. The ESA makes it unlawful for a person to take a listed animal without a permit. Take is defined as "to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect or attempt to engage in any such conduct."

If convicted criminally, the federal penalty is up to one year of imprisonment, $100,000 fine per individual or $200,000 per organization. In addition, State of Florida Statute 372.0725 makes it a third-degree felony to kill or wound any species designated as endangered or threatened. The state penalty is up to five years in jail and/or up to a $5,000 fine.