Northern Prairie Wildlife Research Center
Population Trends for Prairie Pothole Carnivores
Since settlement of the prairie pothole region of the northern Great Plains by Europeans in the late 1800's, carnivore populations have changed considerablymostly due to habitat alteration and human-inflicted mortality. At least 19 species of carnivorous mammals once occurred in the prairie pothole region (Jones et al. 1983). Presently, only eight are common throughout the regioncoyote, red fox, raccoon, American badger, striped skunk, mink, ermine, and long-tailed weasel (Sargeant et al. 1993). Other species that occur locally or intermittently are mountain lion, lynx, bobcat, gray wolf, gray fox, swift fox, spotted skunk, and least weasel. Grizzly bears, wolverines, and river otters once occurred in the region but are now extirpated.
Competition among species affects the distribution of coyotes, wolves, and foxes (Carbyn 1982; Rudzinski et al. 1982, Sargeant et al. 1987; Bailey 1992). These larger canids are keystone species that suppress the distribution of smaller canids (Johnson and Sargeant 1977; Dekker 1989; Johnson et al. 1989).
Human influences on canid communities began in the late 1800's, first with the killing of wolves and later, coyotes, because the predators killed livestock (Johnson and Sargeant 1977; Andelt 1987). Treatment of wolves was especially harsh; consequently, they were essentially eliminated from the prairie pothole region.
Coyotes increased in the prairie pothole region after European settlement and the extirpation of the gray wolf (Bailey 1926; Criddle 1929). Coyotes were numerous in the prairie pothole region in the early 1900's, but populations were noticeably lower by the 1950's and remained low through the 1970's. Population reduction by killing was greatest in farmed areas of the southeastern portion, especially after the 1940's, and some populations were completely eliminated. Survival of coyotes increased after government bans in 1972 of certain predator control methods (Johnson and Sargeant 1977) and with reduced harvest pressure in response to low pelt values in the 1980's. In 1985 and subsequent years, millions of hectares of cropland in the prairie pothole region were enrolled in the Conservation Reserve Program of the U.S. Department of Agriculture (Young and Osborn 1990). Security provided by these extensive grasslands likely enhanced coyote survival. In the early 1990's, coyotes were present throughout most of the prairie pothole region (Sargeant et al. 1993; Sovada et al. 1995). However, an outbreak of sarcoptic mange is now causing declines in coyote populations in North Dakota (Allen 1996) as well as in adjacent states and Canadian provinces. This outbreak may lead to notable population changes in coming years.
In the prairie pothole region, red fox population trends are generally opposite those of coyotes (Fig. 3), Red fox populations expanded greatly in the prairie pothole region between the 1890's and 1930's, especially in the southern portion; expansion began in the 1950's in the northern portion, especially in the northeast (Bird 1961; Johnson and Sargeant 1977). Red foxes were abundant throughout the eastern part of the prairie pothole region between the 1940's and 1970's. In the late 1970's to mid-1980's, red fox populations declined in the prairie pothole region during periods of high fur prices (Sargeant 1982). More recently, red fox populations have declined in the southern portion, apparently in response to competition from increased coyote populations (Sovada et al. 1995). Mange is expected to affect red fox populations in coming years (Allen 1996),
|Fig. 3. Number of re foxes and coyotes seen per hour during winter aerial deer censuses in the Missouri Coteau of North Dakota (information from North Dakota Outdoors).|
Striped skunk populations fluctuate erratically throughout the prairie pothole region (Rosatte 1987; Sargeant et al. 1993). Striped skunks are solitary, except in winter when they may occupy communal dens (Verts 1967). Recorded densities of adults in North Dakota in spring ranged from 1.2 to 1.5 animals per square kilometer, but densities were difficult to estimate because of the species' movements (Greenwood et al. 1985). During April in North Dakota, the minimum home range size averaged 242 hectares for females and 308 hectares for males (Greenwood et al. 1985). Striped skunks were less abundant in the presence of badgers and coyotes, both of which are predators (Sargeant et al. 1982; Johnson et al. 1989). Striped skunks in the prairie pothole region die primarily because of diseases such as rabies, but they are also killed by humans, and some starve to death in the winter (Bjorge et al. 1981, Sargeant et al. 1982; Wade-Smith and Verts 1982). High reproduction (Greenwood and Sargeant 1994) and excellent dispersal (Sargeant et al. 1982) allow striped skunks to rapidly repopulate areas where populations are decimated.
Badgers are at the northern limit of their range in the prairie pothole region (Hall 1981). The presence of badgers is tied to extensive grasslands (Messick et al. 1981; Sargeant et al. 1993), and they avoid cultivated areas (Messick and Hornocker 1981). Burrowing rodents found in grasslands are important prey of badgers (Messick 1987). Badgers are solitary, and little is known of their home range size or density in the prairie pothole region. Their populations in this region seem to have declined significantly since European settlement and have remained relatively low, probably because of the large areas of grassland converted to cropland. Human-inflicted mortality (for example, trapping and shooting) also influences badger populations (Messick et al. 1981). Recently, badgers have extended their range to the east and north in the prairie pothole region, probably as a result of clearing of trees in parkland, draining of wetlands, and increases in rodent populations (Nugent and Choate 1970; Lintack and Voigt 1983; Long and Killingley 1983). Based on numbers of captures in the last 5-10 years, badger populations appear to have increased slightly in the region (U.S. Department of Agriculture, Animal Damage Control, Bismarck, North Dakota, unpublished data). The population increase may be related to extensive grassland habitat provided by the Conservation Reserve Program and to reduced hunting caused by low pelt value.
Mink population sizes are erratic in the prairie pothole region, especially where shallow basin wetlands, their preferred habitat, predominate (Arnold and Fritzell 1987a; Eagle and Whitman 1987; Sargeant et al. 1993). In spring, populations are composed of territorial males that occupy large areas and females that occupy smaller areas (Eagle and Whitman 1987). In the prairie pothole region of Manitoba during May-July, home ranges of male mink averaged 646 hectares (Arnold and Fritzell 1987b) but were larger during the breeding season. Drought reduces mink reproduction (Eberhardt 1974) and has catastrophic effects on their populations (Sargeant et al. 1993). Widespread wetland drainage probably affects mink populations in ways similar to drought.
During the droughts of the 1980's, mink were undetected in many areas of the prairie pothole region (Sargeant et al. 1993). Population lows also probably occurred during the droughts of the 1910's, 1930's, and 1960's. During droughts, rivers and lakes harbor mink populations. The high reproductive potential of mink (Eagle and Whitman 1987) allows the rapid recovery of their populations when prairie wetlands recover from drought. Mink populations likely were extremely low in much of the prairie pothole region of North Dakota in the early 1990's, after the drought of the 1980's. Since 1993, however, populations have begun to recover with improved wetland conditions (M. A. Sovada, U.S. Geological Survey, Jamestown, North Dakota, personal observation),
Populations of weasels fluctuate greatly in response to availability of prey, primarily small mammals (Gamble 1981; Jones et al. 1983). Information on distribution and population trends of weasels is scant. Long-tailed weasel and ermine populations are believed to be fragmented and small throughout the prairie pothole region (Fagerstone 1987; Sargeant et al. 1993). Local occurrence is influenced by prey diversity and abundance, availability of water and den sites, and harvest pressure (Simms 1979; Jones et al, 1983; Fagerstone 1987). Extensive conversion of native uplands and wetlands to cropland probably has reduced the distribution and abundance of ermines and long-tailed weasels throughout the prairie pothole region.
Long-tailed weasel populations appear relatively stable, in contrast to ermine populations, which may fluctuate markedly. This stability reflects the long-tailed weasel's wide range of foods, which differs from the specialist ermine's narrow diet (Simms 1979; Gamble 1981; Fagerstone 1987). From the mid-1980's to early 1990's, the long-tailed weasel was considered threatened in the prairie provinces of Canada as a result of habitat loss and increased use of pesticides (Gamble 1982). However, based on a survey conducted in 1991, Proulx and Drescher (1993) reported the species was present throughout central and southern Alberta. Sargeant et al. (1993) observed large weasels (no distinction was made between long-tailed or ermines) in 20 of 33 study areas in Alberta, Manitoba, Saskatchewan, North Dakota, and South Dakota. The Conservation Reserve Program likely has enabled weasel populations to increase in the southern part of the prairie pothole region.
Raccoons are most common in the southeast part of the region (Sargeant et al. 1993). In spring, density of adult raccoons in North Dakota was estimated at about one or less per square kilometer (Fritzell 1978), Raccoon populations in the prairie pothole region consist of territorial males with large home ranges; females, often attended by young from the previous year, have smaller home ranges (Fritzell 1978). In North Dakota, home ranges of males averaged 2,560 hectares, and those of pregnant females or females with young averaged 806 hectares. Females did not maintain exclusive home ranges.
Raccoons are semiaquatic omnivorous carnivores that have benefited from European settlement of the prairie pothole region. Agricultural crops (cereal grain, corn, and sunflowers) provide a stable food base that replaces mast (fallen nuts on the forest floor) consumed by raccoons in forested areas (Greenwood 1982). Raccoons probably occurred only in riparian and wooded areas in the southeastern portion of the region before European settlement (Bailey 1926). Raccoons were absent in Canada, except possibly in southern Manitoba (Houston and Houston 1973). After European settlement, raccoons became more widely distributed in the southern portion of the prairie pothole region, although populations were low. In the 1940's, raccoons were abundant throughout much of the southeastern portion of the prairie pothole region. In the 1950's, populations in Canada expanded (Lynch 1971; Houston and Houston 1973), and by the 1960's, raccoons were considered a major predator of nesting canvasbacks in southwestern Manitoba (Stoudt 1982). Principal causes of raccoon death in North Dakota are related to human activities (shooting, vehicle impact, and so forth). There is evidence of a negative relationship between coyotes and raccoons (Johnson et al. 1989), suggesting that coyotes may suppress raccoon populations. Suppression of coyotes in the 1950's may have contributed to the range extension of raccoons.
Greenwood, Raymond J., and Marsha A. Sovada. 1998. Highlight Box: Population Trends for Prairie Pothole Carnivores. Pages 461-463 in M. J. Mac, P. A. Opler, C. E. Puckett Haecker, and P. D. Doran, eds. Status and Trends of the Nation's Biological Resources, Vol. 2. U.S. Department of the Interior, U.S. Geological Survey.
This resource should be cited as:
Greenwood, Raymond J., and Marsha A. Sovada. 1998. Highlight Box: Population Trends for Prairie Pothole Carnivores. Pages 461-463 in M. J. Mac, P. A. Opler, C. E. Puckett Haecker, and P. D. Doran, eds. Status and Trends of the Nation's Biological Resources, Vol. 2. Jamestown, ND: Northern Prairie Wildlife Research Center Online. http://www.npwrc.usgs.gov/resource/2000/grlands/grlands.htm (Version 21JAN2000).
We thank H. Umber, North Dakota Department of Fish and Game, Bismarck, for providing his photographs, and North Dakota Outdoors for permission to reprint the information in Figure 3.
See Literature Cited for references
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