Seven Key Largo wood rats have found a new home in the Upper Keys.

For the first time, wood rats born in captivity were released into the wild, taking up permanent residency in the species' native habitat at Crocodile Lake National Wildlife Refuge last week. The seven are part of a planned 14 to be released, refuge officials said. The remaining rats are scheduled to be taken to the refuge on Feb. 22.

The seven wood rats taken to Crocodile Lake were adapting to their new home, working hard on their nests, with most of them making use of as much native vegetation as they were given, U.S. Fish and Wildlife Service spokesman Ken Warren said.

The Key Largo wood rat historically inhabited tropical hardwood hammock forests throughout Key Largo south to Tavernier. The furry rodent was listed as federally endangered in 1984 because of habitat development pressure. Additional threats have emerged since then, including non-native predators such as free-roaming cats and Burmese pythons, Warren said.

After a severe population decline -- an estimated less than 90 remained -- the U.S. Fish and Wildlife Service initiated a captive breeding program in 2002 at Tampa's Lowry Park Zoo and in 2005 at Disney's Animal Kingdom near Orlando.

Breeding Key Largo wood rats was a challenge, because little was known about the social structure, reproductive biology or ecology of the elusive nocturnal species. Key Largo wood rats are atypical for rodents. They are social, and females appear to tolerate the presence of males only for breeding, Warren said. When breeding is successful, females typically produce only two litters per year, with one to three pups per litter.

This conservation initiative was successful and nearly two dozen pups were reared at the zoo, said David Murphy, zoo veterinarian.

"Conservation starts at home, and it's an exciting time to see this program come full circle with the release of captive-born wood rats into their native habitat," Murphy said.

Upon arrival at Crocodile Lake, the Key Largo wood rats were placed in individual enclosures with nest structures designed and built by refuge volunteers. Each animal will be fed for about seven days until the enclosures are removed.

tohara@keysnews.com