Cats Are Obliterating Florida's Endangered Wood Rats

Scientists had hoped a captive breeding program could save the Key Largo wood rat—but even that is unlikely to work.

(Photo: Rob & Ann Simpson/Getty Images)

Jan 28, 2014· 3 MIN READ
Richard Conniff is the author of House of Lost Worlds: Dinosaurs, Dynasties, and the Story of Life on Earth and other books.

In tales of the cat and the rat, society has almost always taken the side of the cat. That has largely continued to be the case in Key Largo, Fla.—with disastrous results for wildlife. The Crocodile Lake National Wildlife Refuge there is one of Florida’s last remaining stands of hardwood hammock forest and home to two highly endangered mammal subspecies—the Key Largo wood rat and the Key Largo cotton mouse.

Right next door to the refuge is a gated community called the Ocean Reef Club, largely developed since the 1960s. Many of its wealthy residents believe they have a right not just to let their own cats roam free but also to feed and care for stray or feral cats in the area. The home owners have maintained that cats do no damage and that roaming free is simply natural for cats. Camera traps have repeatedly shown the cats climbing onto the wood rats’ nests, waiting, and leaping to the attack. Even talking about the effect of house cats on native wild rats has, however, become such an emotional issue that a new study in the journal Biological Conservation carefully avoids ever even mentioning the word “cat.”

Instead, University of Florida wildlife ecologist Robert McCleery and his coauthors focus on the elaborate efforts people have made to save the wood rat from extinction, in spite of the cats. Their results suggest that what had seemed to be the best hope for recovery—a captive breeding and release program—may offer no hope at all.

The U.S. Fish and Wildlife Service began taking wood rats from the wild in 2002, to establish the first captive breeding colony of the subspecies, at Lowry Park Zoo in Tampa. Disney’s Animal Kingdom later established a second colony. The Key Largo wood rats are about as charismatic as rats get, cinnamon colored and with big, glossy black eyes. Disney featured an educational program for children about them as part of its tourist attraction in Orlando.

But according to the new study, both programs eventually failed. The Key Largo wood rats lived far longer in captivity—three years versus an average of less than a year in the wild. So the reasonable assumption was that the population would grow faster in captivity than in the wild. That has been the case in the past for two flagship efforts to save endangered species—the California condor and the black-footed ferret. But Key Largo wood rats did not breed well in captivity, with fewer than half the females ever giving birth.

Even worse, when 41 wood rats born in captivity were released back into the wild over a two-year period, they almost immediately fell victim to cats and other predators. Captive breeding hadn’t taught them the vigilance and anti-predator behaviors they needed to survive in the wild. The captive breeding effort, which cost millions, according to one refuge manager, shut down in 2012.

For McCleery and his coauthors, the chief lesson from the experience is that it's essential to establish beforehand whether the probable benefits of a proposed captive breeding program outweigh the immediate loss caused by removing animals from the wild. That is, does computer modeling with the best available information indicate that captive breeding has a reasonable chance of expanding the existing population? Or could it move a species closer to extinction, as seems to have happened with the Key Largo wood rat?

According to staff biologist Sandra Sneckenberger, the U.S. Fish and Wildlife Service hopes to use McCleery’s recommendations in the near future, as it decides whether to establish a captive breeding program in the Everglades for the Florida grasshopper sparrow, said to be the most endangered bird in the continental U.S. “Looking at both removals and releases at the same time and modeling different scenarios is a smart approach,” she said.

The other big lesson from the Key Largo wood rat experience is the one McCleery and his coauthors avoid: Even the best-planned and -funded recovery effort cannot protect any small species if people continue to feed and protect a large population of an introduced killer such as the house cat right next door.

FWS has attempted to deal with the problem diplomatically. It traps cats on the refuge and delivers them to a nearby animal shelter. The shelter returns identifiable cats to their owners, neuters others for adoption, and euthanizes some unclaimed cats.

Ocean Reef Club continues to practice “trap neuter release” on its own property and claims that this has caused a “dramatic” decrease in its cat population, to 350 feral cats.

Once captured, many of the cats become trap-shy, making recapture difficult, according to refuge manager Jeremy Dixon. But the same animals turn up again and again on camera traps. To protect the wood rats, FWS now builds artificial nests fortified against attack. It also sends out letters to owners of recognized cats warning them that they risk fines for harassing an endangered species. So far FWS has not fined anyone, nor has it made a politically risky stand against the failed practice of “trap neuter release.”

The new study estimates that 78 to 693 Key Largo wood rats remain in the wild. Will this subspecies go extinct? It depends on whether humans, who arrived in Key Largo only recently in the grand scheme of things, decide that an animal with tens of thousands of years of evolutionary history in the habitat has a right to continue surviving there, and that Key Largo will be a better place for having it. (Among other functions, wood rats play a key role in distributing seeds around the hardwood hammock forest, speeding recovery after hurricanes or other disasters.) But plenty of precedent says Key Largo wood rats should not count on our protection.