"When we kept looking at the data, what we found was that you really couldn’t breed enough woodrats to make [captive breeding] a viable strategy for population recovery," says Robert McCleery. (Credit: U. Florida)

Captive breeding won’t save endangered woodrat

Captive breeding may not be the best way to save endangered Key Largo woodrats, which have been driven to near-extinction by development.

Using a computer model, scientists developed a captive breeding-and-release program to see if adding captive-reared animals outweighed the loss of rats from the wild. It didn’t.

Researchers estimate that fewer than 500 of the woodrats remain—down from US Fish and Wildlife Service estimates of about 6,000 in 1984.

Federally-endangered Key Largo woodrats are important to the ecosystem because they spread seeds in a unique forest ecosystem, their stick nests create shelter and habitat for other species, and they are important prey for other species, such as snakes and hawks.

For the study published in the journal Biological Conservation, researchers simulated what woodrats would do in the wild, how they behave in captivity, and what happens when they’re released back into their natural habitat.

“When we kept looking at the data, what we found was that you really couldn’t breed enough woodrats to make it a viable strategy for population recovery,” says Robert McCleery, assistant professor in wildlife ecology and conservation at the University of Florida.

Woodrat reproduction

Woodrats usually reproduce in the wild, two times a year, with litters of three or four. In captivity, they averaged less than one offspring per female per year. When some animals are not in their natural environments, meaning they don’t eat their usual foods or respond to their usual cues, they don’t reproduce.

However, the study may have a silver lining, McCleery says. A captive breeding program may help buffer the woodrat population against catastrophic events such as hurricanes or drought. The woodrat builds and lives in stick nests in tropical hardwood hammocks on about one-third of Key Largo.

Commercial and residential development in the Keys, especially on Key Largo, eliminated much of the woodrat’s habitat, according to the fish and wildlife service. Land has been set aside to protect the woodrat, but even with the protection, its small population and fluctuations make it vulnerable to extinction. Conservationists fear those protections won’t be enough.

The fish and wildlife service established captive breeding colonies and a release program in 2002 at Tampa’s Lowry Park Zoo and at Disney’s Animal Kingdom. When fish and wildlife officers released them, they were much more susceptible to being killed by predators than a normal woodrat.

“In captivity, they can become habituated to people,” McCleery says. Normally, animals should be scared of people. “If you get them to stop responding to scary things, they stop responding to other scary things, like hawks and cats and other natural predators.”

Jeffrey Hostetler, a postdoctoral fellow at the Migratory Bird Center at the National Zoological Park in Washington, DC, who earned his doctorate at the University of Florida, was a co author on the study.

Source: University of Florida

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