Index of Species Information

WILDLIFE SPECIES:  Ondatra zibethicus


WILDLIFE SPECIES: Ondatra zibethicus
AUTHORSHIP AND CITATION : Snyder, S. A. 1993. Ondatra zibethicus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].
ABBREVIATION : ONZI COMMON NAMES : common muskrat water rat rat TAXONOMY : The currently accepted scientific name for common muskrat is Ondatra zibethicus [7]. There are 16 subspecies that differ in population status, distribution, habits, and habitat [14]: 1. O. zibethicus ssp. zibethicus 2. O. zibethicus ssp. albus 3. O. zibethicus ssp. aquilonius 4. O. zibethicus ssp. bernardi 5. O. zibethicus ssp. cinnamominus 6. O. zibethicus ssp. goldmani 7. O. zibethicus ssp. macrodon 8. O. zibethicus ssp. mergens 9. O. zibethicus ssp. obscurus 10. O. zibethicus ssp. occipitalis 11. O. zibethicus ssp. osoyoosensis 12. O. zibethicus ssp. pallidus 13. O. zibethicus ssp. ripensis 14. O. zibethicus ssp. rivalicius 15. O. zibethicus ssp. spatulatus 16. O. zibethicus ssp. zalophus ORDER : Rodentia CLASS : Mammal FEDERAL LEGAL STATUS : None OTHER STATUS : Information on state- and province-level protection status of animals in the United States and Canada is available at NatureServe, although recent changes in status may not be included.


WILDLIFE SPECIES: Ondatra zibethicus
GENERAL DISTRIBUTION : Common muskrats are distributed across North America from northern Alaska and Canada south to parts of the Gulf Coast and northern portions of Mexico [1]. They are found in northern and central California, parts of southern Arizona, northern Utah and Nevada, most of New Mexico, the Texas Panhandle, and eastern Texas, and a small part of western Texas and the Louisiana coast. Common muskrats are not found in Florida or coastal Georgia and South Carolina [14]. Ranges for each subspecies are given below [14]: 1. O. z. zibethicus - eastern U.S. and southeastern Canada 2. O. z. albus - Manitoba and adjacent central Canada 3. O. z. aquilonius - Labrador and adjacent Ungava and Quebec 4. O. z. bernardi - Colorado River areas of southeastern California, southern Nevada, and western Arizona and Mexico 5. O. z. cinnamominus - Great Plains 6. O. z. goldmani - southwestern Utah, northwestern Arizona, and southeastern Nevada 7. O. z. macrodon - mid-Atlantic Coast 8. O. z. mergens - northern Nevada and parts of adjacent states 9. O. z. obscurus - Newfoundland 10. O. z. occipitalis - coastal Oregon and Washington 11. O. z. osoyoosensis - Rocky Mountains and southwestern Canada 12. O. z. pallidus - southcentral Arizona and west-central New Mexico 13. O. z. ripensis - southwestern Texas and southeastern New Mexico 14. O. z. rivalicius - southern Louisiana, Mississippi coast, western Alabama, and eastern Texas 15. O. z. spatulatus - northwestern North America 16. O. z. zalophus - southern Alaska ECOSYSTEMS : FRES17 Elm-ash-cottonwood FRES18 Maple-beech-birch FRES28 Western hardwoods FRES36 Mountain grasslands FRES37 Mountain meadows FRES38 Plains grasslands FRES39 Prairie FRES40 Desert grasslands FRES41 Wet grasslands FRES42 Annual grasslands FRES44 Alpine STATES :
BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 7 Lower Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : K049 Tule marshes K073 Northern cordgrass prairie K074 Bluestem prairie K075 Nebraska Sandhills prairie K077 Bluestem - sacahuista prairie K078 Southern cordgrass prairie K090 Live oak - sea oats K101 Elm - ash forest K114 Pocosin SAF COVER TYPES : 16 Aspen 63 Cottonwood 108 Red maple 217 Aspen 235 Cottonwood - willow SRM (RANGELAND) COVER TYPES : NO-ENTRY PLANT COMMUNITIES : Common muskrats inhabit wetland plant communities comprised of cattail (Typha spp.), bulrush (Scirpus spp.), sedge (Carex spp.), reed (Phragmites spp.), cordgrass (Spartina spp.), saltgrass (Distichlis spicata), and black rush (Juncus roemerianus) [1,14].


WILDLIFE SPECIES: Ondatra zibethicus
TIMING OF MAJOR LIFE HISTORY EVENTS : Breed - March through October, peaking from March through June Age of Maturity - from 6 to 8 weeks or 1 year Gestation - 28 to 30 days Litter - 4 to 7 kits north of 37 degrees north latitude, with 3 or fewer litters per year; 3 to 4 kits south of 37 degrees north latitude, with 3 or more litters per year; young are altricial Weaning - 4 weeks Life Span - up to 4 years in the wild [14] PREFERRED HABITAT : Common muskrats prefer sloughs, marshes, oxbow lakes, streams, levees, dikes, and small lakes and ponds [1]. Along the Gulf Coast, they prefer brackish marshes over freshwater marshes. Common muskrats build lodges in or near water (within 3.3 feet [1 m]), using marsh vegetation. Alternatively, they construct elaborate bank burrows that may be up to 45 feet (15 m) long [1,14]. Entrances to both lodges and burrows are usually under water, and both are multichambered. During periods of low water, common muskrats dig canals from lodges and burrows to deeper water areas. They also build feeding platforms to get out of the water to eat, or feeding huts for protection from the elements and predators [14]. Common muskrats will usually stay within 45 feet (15 m) of their lodges while foraging, although they can range out to 550 feet (183 m). Habitat suitability index models have been developed for common muskrats inhabiting inland freshwater and Atlantic or Gulf coast estuarine areas [1]. COVER REQUIREMENTS : Common muskrat populations tend to be higher in areas with dense aquatic, emergent vegetation that is surrounded by terrestrial herbaceous vegetation. Forested riverbanks usually do not support common muskrat populations. High quality habitat is characterized by 50 percent or more of an area having dense emergent species, although if habitats become "choked" with vegetation, common muskrat numbers will be low. Ideal ratios for vegetation to water are 75:25 to 80:20 [1]. Water levels and velocities affect common muskrat habitat [14]. Typically, if levels are too low, food availability will also be low. This is most pronounced in winter when low water levels allow freezing of the substrate, killing food and cover species [1,14]. Stream gradients and velocities were studied in Massachusetts to determine habitat selection by common muskrats. Streams with gradients more than 47.5 feet per mile (9.0 m/km) and flows less than 4 cubic feet per second (cfs) (0.1 m3/sec) did not support common muskrats. However, common muskrats were found in streams with gradients less than 32.2 feet per mile (6.1 m/km) and flows greater than 4 cfs. River habitats with flows greater than 1,000 cfs (28 m3/sec) typically experience scouring and water level fluctuations too great to support common muskrat populations [1]. In some cases more than a 2-foot (0.6 m) rise in lake levels forces common muskrats out of burrows and lodges, although some fluctuation is necessary for regeneration of emergent vegetation [1]. Lake and pond depths of between 18 inches and 4 feet (0.46-1.2 m) may be ideal. Islands and coves can usually provide additional shoreline and more vegetation for food and cover than bodies of water without these features. Recommended water depths in Gulf coastal marshes are 0.8 to 11.8 inches (2-30 cm) year-round. Levels should not fall more than 3.1 inches (8 cm) below the substrate so that Olney bulrush (Scirpus olneyi), a highly preferred food for common muskrats, can regenerate [1]. Common muskrats need emergent vegetation and a firm substrate for building lodges [1]. They rarely use submergent vegetation. Optimum sites for bank burrows are on slopes of 30 degrees or more, with a minimum height of 1.6 feet (0.5 m). Maximum breeding density for common muskrats is 5 pairs per hectare [14]. FOOD HABITS : Common muskrats eat the basal parts, rhizomes, and leaves of aquatic emergent vegetation. Although they consume mostly plant material, they eat some fish, crustaceans, dead birds, and frogs [14]. In Gulf coastal marshes, Olney bulrush is an important food [16]. Plant food species vary with common muskrat distribution, but some of the major foods are cattail, bulrush, sedge, arrowhead (Sagittaria spp.), waterlily (Nymphaea spp.), wild rice (Zizania aquatica), sweetflag (Acorus calamus), pondweed (Potamogeton spp.), pickerelweed (Pontederia cordata), spikerush (Eleocharis spp.), smartweed (Polygonum spp.), clover (Trifolium spp.), bluestem (Andropogon spp.), rice (Oryza spp.), panicgrass (Panicum spp.), paspalum (Paspalum spp.), burreed (Sparganium spp.), millet (Echinochloa spp.), willow (Salix spp.), poplar (Populus spp.), and some crops. They also consume acorns and maple (Acer spp.) samaras [1,14,16]. PREDATORS : Common muskrat predators include humans, mink (Mustella vison), raccoon (Procyon lotor), bobcat (Felix rufus), house cat (F. domesticus), domestic dog (Canis familiaris), coyote (C. latrans), red fox (Vulpes vulpes), barn owl (Tyto alba), barred owl (Strix varia), great horned owl (Bubo virginianus), northern harrier (Circus cyaneus), bald eagle (Haliaeetus leucocephalus), eastern cottonmouth (Agkistrodon piscivorus), alligator (Alligator mississippiensis), snapping turtle (Chelydra serpentina), bullfrog (Rana catesbeiana), garfish (Lepisosteus spp.), bowfin (Amia calva), and largemouth bass (Micropterus salmoides) [14]. Common muskrats will kill the young of other common muskrats when populations are too dense. MANAGEMENT CONSIDERATIONS : A variety of animals use common muskrat lodges including snakes, turtles, toads, Canada geese (Branta canadensis), and black terns (Childonias niger) [14]. Common muskrats can reduce cattail enough to allow purple loosestrife (Lythrum salicaria), an undesirable weed, to replace cattail and degrade marsh quality [15]. Management of water levels can have a strong impact on common muskrat habitat because of fluctuation influences on certain food species [14]. Drawdowns can have a negative impact on common muskrat populations [17]. Low water levels may encourage undesirable species to take over. Prolonged flooding can destroy food plants [14]. Water levels in Louisiana coastal marshes strongly influence the distribution of Olney bulrush [13]. Recommended water levels for these areas are between 0.5 to 2.0 inches (1.3-5.0 cm), and never less than 2.0 to 3.1 inches (5-8 cm) below the substrate [13,14]. Recommended water levels for Maine are between 6 and 20 inches (15-51 cm) [14]. For detailed information on how water levels affect cattail refer to Weller [19]. For more detailed information on general affect of water level refer to Perry [14]. Common muskrat populations tend to follow a roughly six- to 14-year cycle, where low numbers leading to good food supplies are followed by a population boom and a subsequent decline in common muskrat numbers [4,14]. In Gulf coastal marshes these booms cause "eat-outs", which are areas of extensive overharvest of Olney bulrush by common muskrats. This usually occurs in pure Olney bulrush stands, and can have a detrimental impact on stands. Bulrush must establish within 5 months after an "eat-out" occurs or it will die out [16]. Regeneration can occur through sprouting from rhizome fragments in the substrate. Prolonged flooding can delay regeneration in "eat-out" areas. For more in-depth discussion on management of Olney bulrush refer to Sipple [16]. In some areas mosquito control projects can destroy marshes, as can dredging, diking, and urban sprawl [15].


WILDLIFE SPECIES: Ondatra zibethicus
DIRECT FIRE EFFECTS ON ANIMALS : Common muskrats can be killed by fire either through direct mortality or complete kill of food and cover [12]. The latter was observed in Louisiana peat marshes with shallow clay pans during drought years. When detritus accumulates and fire ignites during dry spells, the fire can burn intensely and move rapidly, killing common muskrat populations [12]. HABITAT RELATED FIRE EFFECTS : Periodic marsh burning is usually necessary to remove dead vegetation, cycle nutrients, and increase vigor of desirable plant species. Conversely, if detritus is allowed to accumulate, fires can become severe enough to destroy desirable species [12]. Mid-July burning of marshes "choked" with common reed (Phragmites communis) in Manitoba resulted in an increase of common muskrat populations [18]. Reed did not reach preburn densities until 4 years later. Olney bulrush increases in cover following burning [10,16]. If this species is not periodically burned, it can be replaced by needlerush (Eleocharis acicularis), sawgrass (Cladium jamaicense), and pineland threeawn (Aristida stricta), which are less desirable food and cover species for common muskrats. Seventy-five to 100 percent of needlerush, sawgrass, and pineland threeawn can be removed by fire [14]. Burning saltmeadow cordgrass (Spartina patens) will remove it, allowing for succession by Olney bulrush. Cordgrass outcompetes Olney bulrush in the absence of fire [16]. Burning cordgrass and saltgrass (Distichlis spicata) during "normal" water levels may not be as effective as burning when water levels are lower in the fall, or until late spring following a flooding treatment with water levels between 10 and 15 inches (25.4-38.1 cm) [16]. FIRE USE : Fire can be used to set back succession of marshes (common muskrats thrive in early seral vegetation stages), prevent the accumulation of detritus, control undesirable species, and promote good growing conditions for Olney bulrush [8,14]. When burning Olney bulrush stands, it is best to leave 0 to 2 inches (5 cm) of standing water, and burn between mid-October and the first of January [12,16]. Olney bulrush grows throughout the winter, and burning just before or during this time will give it a good advantage over other species. Burning dates will vary for different areas, and burning may be necessary every year or two except during times of drought [16]. When burning to eliminate needlerush, do so in late February or early March and when it is dry enough so that needlerush is damaged [14]. Switchgrass (Panicum virgatum) and Olney bulrush should establish by the second or third postfire year. Burning Atlantic coastal marshes is recommended in late winter to ensure adequate winter cover for common muskrats [14].


WILDLIFE SPECIES: Ondatra zibethicus
REFERENCES : 1. Allen, Arthur W.; Hoffman, Robert D. 1984. Habitat suitability index models: muskrat. FWS/OBS-82/10.46. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 27 p. [21637] 2. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434] 3. Chabreck, Robert H. 1968. The relation of cattle and cattle grazing to marsh wildlife and plants in Louisiana. Proceedings, Annual Conference Southeastern Association of Game and Fish Commissioners. 22: 55-58. [14503] 4. Errington, Paul L.; Siglin, Roger J.; Clark, Robert C. 1963. The decline of a muskrat population. Journal of Wildlife Management. 27(1): 1-8. [17542] 5. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905] 6. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998] 7. Honacki, James H.; Kinman, Kenneth E.; Koeppl, James W., eds. 1982. Mammal species of the world. Lawrence, KA: Allen Press Inc. 694 p. [13703] 8. Kelleyhouse, David G. 1979. Fire/wildlife relationships in Alaska. In: Hoefs, M.; Russell, D., eds. Wildlife and wildfire: Proceedings of workshop; 1979 November 27-28; Whitehorse, YT. Whitehorse, YT: Yukon Wildlife Branch: 1-36. [14071] 9. Kuchler, A. W. 1964. United States [Potential natural vegetation of the conterminous United States]. Special Publication No. 36. New York: American Geographical Society. 1:3,168,000; colored. [3455] 10. Lay, Daniel W.; O'Neil, Ted. 1942. Muskrats on the Texas coast. Journal of Wildlife Management. 6(4): 301-311. [14561] 11. Messier, Francois; Virgl, John A. 1992. Differential use of bank burrows and lodges by muskrats, Ondatra zibethicus, in a northern marsh environment. Canadian Journal of Zoology. 70(6): 1180-1184. [18437] 12. O'Neil, Ted. 1949. The muskrat in the Louisiana coastal marshes. New Orleans, LA: Louisiana Department of Wildlife and Fisheries, Fish and Game Division, Federal Aid Section. 152 p. [18182] 13. Palmisano, Angelo W., Jr.; Newsom, John D. 1968. Ecological factors affecting occurrence of Scirpus olneyi and Scirpus robustus in the Louisiana coastal marshes. Proceedings, 21st Annual Conference of Southeastern Association of Game and Fish Commissions. 21: 161-172. [15303] 14. Perry, H. Randolph, Jr. 1982. Muskrats. In: Chapman, Joseph A.; Feldhamer, George A., eds. Wild animals of North America: Biology, management, and economics. Baltimore, MD: The Johns Hopkins University Press: 282-325. [21638] 15. Rawinski, Thomas J.; Malecki, Richard A. 1984. Ecological relationships among purple loosestrife, cattail and wildlife at the Montezuma National Wildlife Refuge. New York Fish and Game Journal. 31(1): 81-87. [18330] 16. Sipple, William S. 1979. A review of the biology, ecology, and management of Scirpus olneyi. Vol. II: a synthesis of selected references. Wetland Publication No. 4. Annapolis, MD: Maryland Department of Natural Resources, Water Resources Administration, Wetlands Permit Division. 85 p. [20021] 17. Thurber, Joanne M.; Peterson, Rolf O.; Drummer, Thomas D. 1991. The effect of regulated lake levels on muskrats, Ondatra zibethicus, in Voyageurs National Park, Minnesota. Canadian Field-Naturalist. 105(1): 34-40. [19873] 18. Ward, P. 1968. Fire in relation to waterfowl habitat of the delta marshes. In: Proceedings, annual Tall Timbers fire ecology conference; 1968 March 14-15; Tallahassee, FL. No. 8. Tallahassee, FL: Tall Timbers Research Station: 255-267. [18932] 19. Weller, Milton W. 1975. Studies of cattail in relation to management for marsh wildlife. Iowa State Journal of Research. 49(4): 383-412. [18158] 20. U.S. Department of the Interior, Fish and Wildlife Service. 1994. Endangered and threatened wildlife and plants; animal candidate review for listing as endangered or threatened species; proposed rule. 50 CFR Part 17. Tuesday, November 15, 1994. Federal Register. 59(219): 58982-59028. [24357]

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