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Neofiber alleni

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA RODENTIA CRICETIDAE

Scientific Name: Neofiber alleni
Species Authority: True, 1884
Common Name(s):
English Round-tailed Muskrat
Taxonomic Notes: Whitaker and Hamilton (1998) recommended that subspecies nigrescens and struix be regarded as synonyms of alleni.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2011
Date Assessed: 2008-07-01
Assessor(s): Linzey, A.V. & NatureServe (Jackson, D.R., Bergstrom, B. & Hammerson, G.)
Reviewer(s): Amori, G. & Chanson, J.S.
Justification:
Listed as Least Concern as it is common to rare within its large range, it occurs in many protected areas, and its population is not declining fast enough to qualify for listing in a more threatened category.

Geographic Range [top]

Range Description: The Round-tailed Muskrat occurs in Florida and south-central and southeastern Georgia, ranging west to at least the Choctawhatchee River in Walton County, Florida (Lefebvre and Tilmant 1992). It is apparently most common in the Everglades region of Florida and the Okefenokee Swamp of Georgia.

Bergstrom et al. (2000) concluded that the range is fairly continuous within suitable habitat from north-central Florida into south-central Georgia. There seems to be a gap of about 80 km between the Grand Bay population in south-central Georgia and the Okefenokee population to the east, though apparently suitable habitat is present in the gap (Bergstrom et al. 2000). The apparent gaps at the northern range limit may be the result of a combination of the fragmented, isolated distribution of palustrine wetlands and the generally low population densities causing localized extinction (Bergstrom et al. 2000). Habitats in Georgia may be peripheral dispersal sinks, occupied only following periods of exceptionally high densities in more central populations (Bergstrom et al. 2000). New localities in south-central Georgia (mainly the Grand Bay population) are closer to being contiguous to the previously described range of subspecies apalachicolae to the southwest in north Florida than to the range of subspecies exoristus, known from the eastern Okefenokee Swamp in Georgia (Hall 1981). The possibility exists that a large and viable population survives in the 30,000 ha of wet prairies and islands of the Okefenokee Swamp (only a fraction of which is actually suitable habitat); Harper (1927) estimated the population at 10,000, but Porter (1953) found very few signs of active houses and recent observations by T. Hon conform with Porter's findings. Georgia colonies that were reported in years past from southern Thomas County (W. Baker pers. comm.) and southwestern Lowndes County (T. Hon pers. comm.) were not found in recent aerial surveys (Bergstrom et al. 2000). Harper (1920) documented Neofiber in "prairie" habitats on the eastern side of the Okenfenokee Swamp. Schantz and Jenkins (1950) reported Neofiber skulls in barn owl pellets near Woodbine, Camden County (on the Satilla River, about 20 miles from the Atlantic Coast).
Countries:
Native:
United States (Florida, Georgia)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: In Florida, this species is locally common on St. Johns marsh in Brevard County, near Hawthorne in Putnam County, and in the Lake Okeechobee region. Highest densities reported are for sugar cane fields in south Florida. In the sugarcane-growing region of Florida, the species is most common in western and northeastern Palm Beach County. It is apparently rare to absent and of spotty occurrence along the upper west Gulf Coast of Florida (Taylor and Suwannee counties south to Hillsborough County), in west-central Florida (Hillsborough, Polk, Manatee, Sarasota, and DeSoto counties), and in northeastern Florida (Nassau and Duval counties, and portions of Baker, Clay, and St. Johns counties); populations may be limited in certain formerly occupied coastal marshes where canals and reduced flows have allowed salt water intrusion (Layne 1978). Porter (1953) found Neofiber to be nearly or completely absent from many areas throughout Florida that previously supported dense populations. See Lefebvre and Tilmant (1992) for further details on the distribution in Florida.

The total adult population size is unknown but certainly is at least many thousands. This species is represented by many occurrences or subpopulations throughout much of its former range. Wetlands destruction has slowed in Florida but still occurs. With improved wetland protection, the rate of decline likely is much less than 30% over 10 years or three generations. Area of occupancy, number of subpopulations, and population size probably have declined (Lefebvre and Tilmant 1992), but the extent of decline is uncertain.

Average density is 50 individuals per acre, although peak densities can reach 100-120 per acre (Birkenholz 1972). On smaller natural marshes in central Florida, may reach maximal densities of 250-300/ha, whereas on larger marshes (>1,000 ha) maximal densities are reported as 50/ha (Birkenholz 1963). Ecological densities in Georgia (1-3/ha; Bergstrom et al. 2000) are much lower than the maximal densities reported for Florida (Bergstrom et al. 2000).

Average home-range sizes for 23 radio-tracked Round-tailed Muskrats ranged from 1.263-2,071 m2 in isolated wetlands in south Florida (Schooley and Branch 2006), with individuals using 10-15 different rest sites within each home range. Muskrats typically used lodges for diurnal rest sites when their marsh habitat was inundated with water but switched largely to burrows when marshes dried up.

Local populations often fluctuate tremendously, probably in response to water-level fluctuations and changes in habitat conditions (Lefebvre and Tilmant 1992). May wander or disperse a few or several hundred metres from permanent water. In the dry prairie region of south Florida (on and around Avon Park Air Force Range), Round-tailed Muskrats occupied 35.7% of 457 isolated wetlands in either one or both years of a survey. Local extinction (within a wetland patch) and recolonization occurred in many cases. Patch occupancy increased as patch size, spatial connectivity, and habitat quality increased (Schooley and Branch 2007). Cattle grazing can reduce habitat quality by removing key food and house-building plants such as Panicum sp. Dry prairie habitat of high quality—as the matrix surrounding isolated wetland habitats of Round-tailed Muskrat—was judged to facilitate recolonization of patches, whereas pine plantations were barriers to recolonization (Branch and Schooley 2005).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Round-tailed Muskrats are a semi-aquatic species, preferring heavily vegetated freshwater habitats and restricted to permanent water bodies free of freezing (Hafner et al. 1998). Typically they occur in shallow grassy salt/freshwater marshes. In Florida, dense stands of maidencane (Panicum hemitomon) and pickerelweed (Pontederia lanceolata) provide preferred habitat (Layne 1978); other habitats include salt marshes on Merritt Island National Wildlife Refuge and on Cape Sable (status in salt marshes on the northern Gulf coast needs further study). Pocosins and Carolina bays with a history of fire (i.e., not succeeding toward dense shrub bog) provide ideal habitat (Bergstrom et al. 2000). At Grand Bay, Georgia, Round-tailed Muskrats inhabit floating mats of bog like vegetation surrounded by open-water emergent marsh dominated by sedges such as Carex and Eleocharis spp.; these finer sedges are preferred house-building materials, whereas the coarser grass Panicum is preferred in Florida. The species is most abundant in areas with water 6-18 inches deep and a sandy, peaty, or soft substrate deep enough to allow burrowing to water during dry periods (Birkenholz 1972, Porter 1953).

Dome-shaped houses, used for shelter and rearing young, are built among emergent vegetation; most house repair and new construction occur in spring. In south-central Georgia, houses are attached to the surfaces of floating mats of Sphagnum and organic muck or to the bases of shrubs or small trees (Harper 1927, Birkenholtz 1963, Bergstrom et al. 2000). In sugarcane fields, houses, if present, are smaller and more rudimentary. Round-tailed Muskrats also build extensive tunnel systems in drained muck soils of sugarcane fields and agricultural areas.

These muskrats construct floating feeding stands near house sites. In Georgia, denuded areas usually close to the edge of the mat were used as feeding stations. Round-tailed Muskrats are able to disperse between areas of suitable habitat across roads and small expanses of upland habitat and via ditches (Birkenholz 1963).

This species breeds year-round, with a peak in late fall. May-November live-trapping in sugarcane fields yielded the largest number of juveniles and subadults in May (Lefebvre and Tilmant 1992). Gestation lasts 26-29 days. Litter size is 1-4 (average two); 4-6 litters per year. Sexually mature in 90-100 days. Reproductive potential is relatively low.

Round-tailed Muskrats are apparently colonial in both marshes and muck fields. There is an average of about two houses for each individual, and generally no more than one adult uses each house. Burrow systems are occupied usually by single adults, a pair, a female and young, or one to two subadults (Lefebvre and Tilmant 1992). Home range is less than 2.5 acres. They are vulnerable to various reptilian, avian, and mammalian predators.

They eat roots and stems of aquatic and semi aquatic vegetation; major food plants include arrowheads, pickerelweed, Nymphaea water lilies, maidencane, cut-grass, sedges, and grasses (Panicum, Sporobolus, and Echinochloa). In sugarcane fields, diet apparently is dominated by the sprouts, stalks, and roots of sugarcane, and by sedges and grasses (see Lefebvre and Tilmant 1992). They are primarily nocturnal.
Systems: Terrestrial; Freshwater

Threats [top]

Major Threat(s): The statewide population in Florida probably has declined as a result of wetland loss (Lefebvre and Tilmant 1992). Land fills, marsh drainage, and salt water intrusion have reduced the available habitat and further isolated some colonies (Layne 1978). Isolated populations are very vulnerable to extirpation caused by natural fluctuations in water levels (Lefebvre and Tilmant 1992); these receive inadequate protection.

Conservation Actions [top]

Conservation Actions: This species occurs in several protected areas, including Okefenokee National Wildlife Refuge, Georgia; Everglades National Park, Florida; Corkscrew Swamp Sanctuary (National Audubon Society), Florida; Paynes Prairie Preserve State Park, Florida; and other Florida managed areas. It is protected from trapping and hunting in Florida and Georgia.

The precise distribution of all occurrences needs to be determined. Representative subpopulations should be monitored. Occupied marsh habitats, including appropriate upland buffers and incoming drainage systems, are in need of further protection.

Citation: Linzey, A.V. & NatureServe (Jackson, D.R., Bergstrom, B. & Hammerson, G.) 2011. Neofiber alleni. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 29 November 2014.
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