Northern Prairie Wildlife Research Center
Waterfowl in the Prairie Pothole Region
The prairie pothole region of the northern Great Plains is one of the most important areas for duck reproduction in North America. The region produces, on average, 50% of the primary species of game ducks on the continent (Smith 1995), yet accounts for only 10% of the waterfowl breeding habitat in North America (Smith et al. 1964). Twelve of the 34 species of North American ducks are common breeders in the region. For seven speciesmallard, gadwall, blue-winged teal, northern shoveler, northern pintail, redhead, and canvasbackthe prairie pothole region accounts for more than 60% of the breeding population (Smith 1995). The region is also a major migration corridor during fall and spring for other ducks, geese, and other water birds.
Annual variations in the number and distribution of ducks are strongly influenced by dynamic water conditions in the prairie pothole region (Batt et al. 1989). Breeding duck population sizes and reproduction are positively related to the number of wetland basins holding water in May and July (Reynolds 1987; Johnson and Grier 1988; Batt et al. 1989). During periods of widespread drought in the grassland portion of the region, many ducks move into the parkland; when both regions are dry, ducks may be displaced to the boreal forest or tundra regions (Johnson and Grier 1988). Species such as pintail and blue-winged teal tend to be more affected by drought conditions because of their preference for temporary and seasonal wetlands, whereas canvasbacks and lesser scaup, which use more stable semipermanent and permanent wetlands, are less likely to be displaced unless drought is severe. For all species, however, productivity is generally reduced during drought conditions because of poorer nesting effort and success and low survival rates of young.
The U.S. Fish and Wildlife Service and Canadian Wildlife Service have conducted annual surveys of breeding waterfowl populations in the principal breeding areas of North America since 1955. The surveys provide data on habitat conditions (numbers of ponds), breeding population sizes, and production. The Waterfowl Breeding Population and Habitat Survey, conducted each May, uses east-west aerial transects spaced within 50 habitat strata (Smith 1995). Data from aerial counts in the region are adjusted for visibility based on results from selected ground survey areas to provide population estimates in each stratum, This annual survey is among the most extensive and comprehensive animal surveys conducted in the world, and it provides an important long-term data base for population and habitat trends and population management. I used these data (Smith 1995) for southern Alberta, southern Saskatchewan, southern Manitoba, eastern Montana, North Dakota, and South Dakota to assess the status and trends of 10 common duck species (mallard, gadwall, American wigeon, green-winged teal, blue-winged teal, northern shoveler, northern pintail, redhead, canvasback, and lesser scaup) over the last decade. Information on Canada geese breeding in the prairie pothole region is derived from May surveys and midwinter counts from the U.S. Fish and Wildlife Service. For information on trends in waterfowl populations before 1986, see Batt et al. (1989).
During the last decade, spring water conditions in the prairie pothole region, as measured by the number of wetland basins holding water (ponds), ranged from good in 1986 (more than 5 million) to very poor during the 1988-1993 drought (3.6 million or less) to excellent by 1994-1995 (Table 1). In 1986 pond numbers were above the long-term averages (1974-1995) for both the U.S. and Canadian portions of the region. Conditions in both areas degraded markedly over the next 3 to 5 years with the onset of drought conditions. Severe drought conditions continued in the United States through 1992, then rebounded dramatically in 1994-1995. Water conditions across much of the region in early 1996 remained good to excellent.
|Table 1. Breeding population estimates for all ducks in the prairie pothole region and estimates of numbers of ponds during May, 1986-1995.|
|Year||Number of breeding ducks||Number of ponds|
Over the past 10 years, the number of breeding ducks in the prairie pothole region averaged 15,195,000 (Table 1), 16% lower than the long-term average (1955-1995) of 18,166,000. Duck numbers were lowest during 1988-1993, when drought conditions were widespread. With the return of heavy precipitation and excellent water conditions in most areas in 1994-1995, duck numbers responded rapidly and exceeded the longterm average by 5% and 20%, respectively.
Numbers of mallards and blue-winged teal were relatively low during the drought but rebounded in 1994-1995 (Table 2). Although the gadwall is more closely associated with the prairie pothole region than other ducks (more than 90% of the continental surveyed gadwall population occurs in the region), gadwall numbers dropped only slightly below their long-term average during 1987-1988; by 1995 gadwall numbers were 111 % above the long-term average (Table 2). Numbers of pintails in the region reached record lows during the drought as large portions of the population were displaced to northern areas, and their reproduction rate was low (Hestbeck 1995). Wigeon numbers in the region changed little over the past decade and remained below their long-term average despite some increase in 1994-1995.
The breeding population of northern shovelers in the prairie pothole region (Table 2) followed a pattern of decline and recovery similar to mallards and blue-winged teal. Green-winged teal populations did not decline markedly during drought years but did increase substantially in 1994-1995. Of diving ducks, lesser scaup showed the greatest response to the drought and the return of good water conditions. Numbers of redheads and canvasbacks were slightly depressed during drought years but, like scaup, responded to the return of good water conditions in 1994-1995, By 1995, redhead and canvasback numbers exceeded longterm averages.
|Table 2. Breeding populations (in thousands) of 10 duck species in the prairie pothole region in 1986-1995 (Smith 1995). TYA = 10-year average; LTA = long-term average (1955-1995).|
Three populations of migratory Canada geese occur in the Great Plains. The Highline population breeds in southeastern Alberta, southwestern Saskatchewan, eastern Montana, eastern Wyoming, and northcentral Colorado. January surveys in Colorado and New Mexico indicated that the Highline population has grown an average of 10% per year over the past 10 years, from about 75,000 geese in 1985 to a record 174,400 geese in 1995 (U.S. Fish and Wildlife Service, unpublished data). The Western Prairie population nests in eastern Saskatchewan and western Manitoba, and the Great Plains population is a restored population breeding in Saskatchewan, North Dakota, Nebraska, Kansas, Oklahoma, and Texas. Because of the way the survey design relates to the breeding range boundaries, separate estimates for these two populations are not available. Estimates from May surveys for ducks suggest that the Western Prairie and Great Plains populations combined in the region have increased from 108,000 in 1986 to 228,000 in 1995 (U.S. Fish and Wildlife Service, unpublished data).
The dynamics of water conditions and duck populations observed over the past decade are characteristic of the prairie pothole region (Lynch 1984). Widespread drought during 1988-1993 reduced wetland habitat available to waterfowl, causing a marked reduction in waterfowl production. Displacement of ducks, particularly pintails and mallards, to northern regions also reduced populations during the drought. Pintail populations also may have been depressed by intensification of agricultural activities (drainage, cropping, and gazing) in key breeding areas (Hestbeck 1995). The dramatic recovery of most duck species in the region in 1994-1995 resulted primarily from heavy precipitation patterns that began in late 1993 and replenished many wetlands, providing abundant food and habitat for breeding ducks.
Two other factors probably were significant in contributing to the large and rapid recovery by most species. First, changes in the predator community have altered predation pressures on nesting waterfowl in many areas (Greenwood and Sovada 1996). After the drought, red fox population sizes were low, favoring high nest success, and mink numbers were also low, enhancing duckling survival. Second, about 1 million hectares of cropland in the U. S. portion of the prairie pothole region were restored to perennial grassland through the Conservation Reserve Program. Fields in the Conservation Reserve Program provide attractive and often highly productive nesting cover for upland-nesting ducks (Kantrud 1993). The combination of good to excellent water conditions, reduced predator pressure, and improved availability of nesting habitat in the United States provided conditions for a dramatic rebound in duck numbers after the drought. However, these conditions are seldom synchronized for more than 2 or 3 years, and such high duck production is likely in on ly 2 or 3 years out of 10 where habitats are altered by agriculture (Lynch et al. 1963). High production of waterfowl, especially of early-nesting species such as mallards and pintails, has become more difficult to achieve during years of moderate water conditions (Lynch 1984; Batt et al. 1989).
The ability of duck populations to recover from naturally occurring droughts has been reduced by continued loss of nesting habitat to agricultural activities, primarily grain cropping and intensified grazing. These agricultural effects are likely to be greatest in the grassland portion of the prairie pothole region, which experiences the greatest variability in water conditions and has had the greatest expansion of agricultural activities (Bethke and Nudds 1995). Whereas parkland and boreal areas can sustain duck populations over time, it is the grasslands' capacity for high duck production during wet periods that is critical to the growth of waterfowl populations (Lynch 1984).
Austin, Jane E. 1998. Highlight Box: Waterfowl in the Prairie Pothole Region. Pages 456-457 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:
Austin, Jane E. 1998. Highlight Box: Waterfowl in the Prairie Pothole Region. Pages 456-457 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).
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