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Neofiber alleni True, 1884
Round-tailed Muskrat
Federal Protection: No US federal protection
State Protection: Threatened
Global Rank: G2
State Rank: S3
Element Locations Tracked in Biotics: Yes
SWAP 2015 Species of Greatest Conservation Need (SGCN): Yes
SWAP 2025 Species of Greatest Conservation Need (SGCN): Yes
2025 SGCN Priority Tier: High Conservation Concern
Element Occurrences (EOs) in Georgia: 13
Habitat Summary for element in Georgia: Freshwater marshes; bogs
Round-tailed muskrats, the only members of the genus Neofiber, have dense, rich dark brown fur turning to gray at the base. The guard hairs are dark brown and glossy, and the belly fur is pale buff. The ears are small, and the front feet are smaller than the slightly webbed rear feet. This rodent grows to be 29 - 38 cm (11½ -15 inches) long, including a round, sparsely haired tail. Adults weigh 200 - 330 grams (7 - 11½ ounces). Males are slightly heavier than females.
The muskrat (Ondatra zibethicus) is larger and the tail is laterally compressed. The ranges of these species do not overlap.
Round-tailed muskrats live in shallow grassy ponds, marshes, and bogs. Preferred habitat appears to be floating mats of vegetation in the vicinity of open water with emergent sedges and floating-leaved vegetation. At Grand Bay in south Georgia, preferred habitat appears to exist mainly along the ecotone between mixed emergent marsh and dense chain-fern marsh. Prairies on the east side of the Okefenokee Swamp also provide good habitat, as do a few other swamps and Carolina bays in the vicinity. The easternmost Georgia occurrence record is of skulls found in barn owl pellets near Woodbine in Camden County.
The diet consists primarily of aquatic grasses, but also includes stems, roots, and seeds of other aquatic plants, and possibly crayfish.
Round-tailed muskrats produce 4 - 6 litters, each containing 1 - 4 young, throughout the year with a peak in late autumn. Gestation lasts 26 - 29 days; young are weaned at about 21 days and are fully mature 90 - 100 days after weaning. Round-tailed muskrats are primarily nocturnal; predators include hawks, owls, alligators, and water moccasins. Round-tailed muskrats weave dome-shaped houses of grasses, sedges, cat-tails, and other aquatic vegetation on floating mats of sphagnum or peat or attached to the bases of shrubs or small cypress trees. The houses measure 30 - 45 cm (12 - 18 in) wide at the base and 25 - 38 cm (10-15 inches) in height and are lined on the inside with fine, dry grasses. Two escape holes typically exit the floor of the house and lead to escape tunnels, or plunge holes, in the vegetation mat. Each muskrat utilizes several houses, and individuals sometimes share houses. They are non-territorial and live in dense colonies where habitat is suitable. During periods of low water, round-tailed muskrats occupy tunnels in the sphagnum mats rather than building houses. Round-tailed muskrats also construct floating feeding platforms, measuring 10 - 20 cm (4 - 8 inches) in diameter, from vegetation. Density estimates vary, depending upon habitat and methodology, from 1 - 3 per hectare (or about 1 per acre) at Grand Bay to 250 - 300 per hectare (100 - 121 per acre) in small central Florida marshes. They can become pests in South Florida sugarcane fields.
Probably the best method to detect this species is by searching for their houses and feeding platforms, which are most easily spotted during the wintertime.
Round-tailed muskrats are found throughout most of southern Florida and have a patchy distribution in the northern part of the state. They can also be found into parts of extreme southern Georgia from Camden County to Brooks County, including Okefenokee Swamp and Grand Bay. Although currently restricted to Florida and southern Georgia, the round-tailed muskrat used to inhabit areas from South Carolina to possibly West Virginia.
South Georgia is on the edge of the range of the round-tailed muskrat, so it is likely that the species has never been abundant there. Urbanization can be a major threat to this species. In a recent study conducted by Faller and McCleery (2016) it was shown that the probability of finding round-tailed muskrats in a wetland decreased significantly with increasing urban development. Greater amounts of urban cover increases the chances of pollution, alters the wetland’s hydroperiod (length and timing of wet and dry seasons), and can disrupt environmental processes. Urban land also has an effect on the plant make-up of a wetland, an important feature for this species. Urbanization seems to promote the growth of dogfennel, a plant negatively associated with round-tailed muskrats, and demote the growth of maidencane, a plant previously suggested to be the dominant food source of round-tailed muskrats in certain parts of their range.
Populations are limited by the amount of suitable floating vegetation mats, so loss of any occupied wetland habitat has a big impact. Habitat can be lost not only through alteration of the natural hydroperiod, draining, and development, but also through natural succession due to lack of periodic fire. Bogs and marshes gradually fill in and are taken over by woody vegetation unless fires retard the process. Under natural conditions, periodic fires, particularly during summer droughts, remove woody vegetation and burn deep holes in the peat. This drives a cyclical process of floating mat and open sedge marsh production so that suitable habitat is continuously created. However, control of naturally occurring fires has interrupted this cycle. Fire ant infestation of floating mats presents another problem, with ants often taking over muskrat houses and probably threatening nestlings. This problem increases as the amount of woody vegetation increases. The size of local round-tailed muskrat populations throughout the species' range apparently fluctuates dramatically as a result of environmental conditions.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Residential & commercial development | Energy production & mining | None |
| Specific Threat | Housing & urban areas | Mining & quarrying | None |
Some of the best round-tailed muskrat habitat is found in the Okefenokee National Wildlife Refuge and at Grand Bay Wildlife Management Area, and habitat there appears relatively secure. However, no recent surveys have been completed so the status of these populations are uncertain.
Maintaining suitable habitat is critical to ensuring the continuing survival of round-tailed muskrats in Georgia. This species has apparently disappeared from many areas because habitat is no longer suitable. Habitat needs to be managed such that high water levels are maintained most of the time, but such that fire can be used during periods of low water to prevent succession to woody vegetation. Winter drought can be important in floating mat production because it exposes the roots of vegetation to freezing temperatures. This kills the plants which later float up as mats. Sandhill cranes probably play a role in maintaining suitable habitat as well by consuming the roots of invasive plants thereby helping keep the mats open. Restricting urban development near suitable wetlands is also needed to maintain a viable habitat for this species.
Bergstrom, B. J., T. Farley, H. L. Hill, Jr., and T. Hon. In press. Ecology and conservation of a frontier population of the round-tailed muskrat (Neofiber alleni). Occasional Publications of the North Carolina State Museum of Natural History, Raleigh.
Birkenholtz, D. E. 1963. A study of the life history and ecology of the round-tailed muskrat (Neofiber alleni True) in north central Florida. Ecological Monographs 33: 225-280.
Birkenholtz, D. E.. 1972. Neofiber alleni. Mammalian Species 15: 1-4.
Chapman, F. M. 1889. On the habits of the round-tailed muskrat (Neofiber alleni True). Bulletin of the American Museum of Natural History 2: 119-122.
Lefebvre, L. W., and J. T. Tilmant. 1992. Round-tailed muskrat. Pages 276-286 in S. R. Humphrey and R. E. Ashton (eds.). Rare and Endangered Biota of Florida, Volume 1, Mammals. University Press of Florida, Gainesville.
Trani, M. K., W. M. Ford, and B. R. Chapman. 2007. The land manager’s guide to mammals of the south. The Nature Conservancy, Durham, North Carolina. 566 pp.
Whitaker, J. O., Jr., and W. J. Hamilton, Jr. 1998. Mammals of the eastern United States. Cornell University Press, Ithaca, New York. 583 pp.
Jim Ozier
J. Ozier, August 2008: Original account
K. Owers, November 2009: Updated status and ranks, added pictures
S. Krueger, March 2020: Added current information and updated ranks
