Species at Risk

They're Not Multiplying Like Rabbits
by Beth Forys, Eckerd College and Susan Jewell, U.S. Fish and Wildlife Service

Imagine a rabbit that is so adept at swimming it can dive under water to avoid predation and can easily swim 100 yards or more. That's what the Lower Keys marsh rabbit has to do to survive on its island home—the Florida Keys.

Historically, the range of this endemic subspecies extended from Big Pine Key to Key West, already a limited range. Habitat destruction, fragmentation, and other human disturbances have further limited the subspecies to a handful of islands. Most of the remaining habitat patches are only a few acres in size and the rabbits must cross roads, canals, and subdivisions to find mates.

This Lower Keys subspecies, Sylvilagus palustris hefneri, was only recently described to science. In 1984, biologist James Lazell determined that the Lower Keys rabbits differed from the Upper Keys ones. He financed his research partially with a grant from Hugh Hefner's Playboy Corporation, which won a bid over Volkswagen, and honored the corporation's founder by naming the new rabbit species after him. Only 6 years after it was described, the rabbit was listed as Federally endangered.

The old adage "multiplying like rabbits" doesn't work well in the Lower Keys, where the local rabbits are not as fruitful as their well-known mainland relative, the eastern cottontail. In above-ground nests made in dense marsh grass, Lower Keys rabbits have litters of two to four young and may produce only three or four litters each year. The population is estimated at 100 to 300.

The Lower Keys marsh rabbit looks similar to marsh rabbits found in peninsular Florida but is smaller, less reddish, and has different cranial measurements. Evidence suggests that its kidneys are better adapted for living with little fresh water.

The transition zone, an area of marshes and grasslands that lies between mangroves and upland hardwood hammocks, is the rabbit's habitat. Both saltwater and freshwater marsh plants occur in this zone, along with bunch grasses, shrubs, and small trees. Marsh rabbits eat nearly every plant from succulent sea-daisies to dry cordgrass to tree leaves.

While most of their habitat is protected by national wildlife refuges and military bases, the greatest threat to the marsh rabbit now appears to be predation. A 3-year live-trapping and radio-telemetry study found that 53 percent of all Lower Keys marsh rabbits (both sexes and all ages) were killed by domestic cats. Some cats may have been feral, receiving only supplemental food from people, while others appeared to be pets out for an evening of entertainment. Another human-related source of mortality was automobiles, although this may be less important because it mainly kills young males rather than reproducing females.

Current recovery efforts are aimed at improving the rabbit's habitat through invasive plant removal and moving rabbits to cat-free islands where they historically occurred. Convincing cat lovers to keep their cats inside at night and reducing the feral cat population may ultimately be necessary to save this important part of the Florida Keys ecosystem.

For more information, contact Dr. Beth Forys, Assistant Professor of Environmental Science and Biology, Eckerd College, 4200 54th Avenue South, St. Petersburg, Florida 33711, (727) 864-7880, forysea@eckerd.edu, or Phil Frank, Recovery Biologist, U.S. Fish and Wildlife Service, P.O. Box 430510, Big Pine Key, Florida 33042, (305) 872-2753, phil_frank@fws.gov, http://verobeach.fws.gov/Programs/Recovery/vbms4.html.