Northern Prairie Wildlife Research Center
We used the habitat data base acquired in 1982 for all years, but adjusted it each year as follows for Cropland and Wetland, because those habitats may undergo substantial annual changes that influence their potential use by ducks for nesting. In the first week of May, we apportioned Cropland into standing stubble, tilled stubble, and fallow land (included spring-planted land that was indistinguishable from fallow at that time). Personnel on the ground visually estimated portions of every quarter-section in each category. Of the 3 types of Cropland, we considered only standing stubble to be suitable as nesting cover; amounts of tilled stubble and fallow land (considered not suitable for nesting) were added to Barren that year to create a class called Unsuitable. Although availability of standing stubble changed during the nesting season because of tillage, we did not change the percentage of Cropland we considered to be suitable as nesting habitat after our May assessment. We calculated the mean percentage of Cropland that was standing stubble annually; means were weighted by area of Cropland available on individual study areas in 1982. We did not adjust Cropland values to reflect increasing presence of growing grain that began to emerge in early to mid-June.
We considered vegetation in temporary and seasonal wetlands to be available for nesting if basins were dry at the time of the annual Waterfowl Breeding Ground Survey in May (see Weather and Wetland Conditions). If temporary and seasonal wetlands were wet in May, we considered them unsuitable for nesting and added the area of those wetlands that year to Unsuitable. We considered emergent vegetation in semipermanent wetlands to be available for nesting in the current year regardless of whether the basin was wet or dry, but considered only 75% of this habitat to be suitable for nesting. Aerial photographs and ground surveillance showed that about 25% of the emergent vegetation in semipermanent wetlands usually was not suitable for nesting (e.g., too sparse); therefore, we reduced the area of emergent semipermanent wetland habitat by 25% each year and added that amount to Unsuitable. Areas of open water also were added to Unsuitable.
|Study area||Size (ha)||Habitat (%)|
|Crop- land||Grass||Brush||Wet- land||Hay- land||Wood- land||Right- of-way||Odd areaa||Barrenb|
|aOdd area included
patches of cover <2ha in size and an array of features usually found in
Cropland (e.g., rock piles, gravel borrow pits, narrow borders
of upland vegetation around Wetland and along fences between
areas of Cropland).
bBarren included all areas not suitable for nesting (e.g., road surface).
Cropland averaged 59% of the landscape on study areas (56% in parkland and 62% in prairie) (Table 2). However, in early May an average of only 16% of the landscape was standing stubble in all area-years (13% in parkland and 20% in prairie). Remaining Cropland had been tilled or was fallow the previous year (Table 3). Standing stubble that we considered suitable as nesting habitat averaged 16% of the landscape in all area-years.
|Study area||Cropland available (ha)||Suitable for nesting (%)|
Grass averaged 19% of the landscape on study areas (Table 2). Largest contiguous areas of Grass on study areas were 4-8km² pastures managed by the Prairie Farm Rehabilitation Administration, municipal agencies, or private landowners on the Ceylon, Gayford, Goodwater, Holden, Leask, Penhold, Shamrock, and Yorkton study areas. Brush was a minor habitat component in areas of native prairie Grass and averaged 1% of the landscape on study areas (Table 2).
Wetland averaged 11% of the landscape on study areas (Table 2), but an average of only 4% of the landscape was Wetland that we considered suitable as nesting cover in all area-years. Estimated density of wetlands ranged from 10/km² on the Leask Study Area to 50/km² on the Moore Park Study Area (Table 4).
|Study area||Estimated no./km²||Wet wetlands (%)|
|aWet implies visible standing water. Data provided by Off. Migr. Bird Manage., U.S. Fish and Wildl. Serv., Laurel, Md., based on assessment conducted in May during annual Waterfowl Breeding Ground Survey (Martin et al. 1979).|
Odd area averaged 5% of the landscape on study areas (Table 2) and tended to be least available on study areas in the prairie where there were few trees to interfere with tillage. In the parkland, Odd area often was composed of narrow bands of shrubs and trees that encircled wetlands in cultivated fields.
Woodland averaged 4% of the landscape in parkland, but was nearly absent (<1%) from most study areas in prairie (Table 2). Contiguous areas of Woodland were seldom >65 ha and most were grazed.
Hayland averaged 3% and Right-of-way averaged 2% of the landscape on study areas (Table 2). Right-of-way was mostly along roads. In most years, forage crops in Hayland and vegetation in Right-of-way were mowed in late June.
Barren averaged 1% of the landscape on all study areas (Table 2). The total area classified as Unsuitable (Barren plus portions of Cropland and Wetland that were not suitable for nesting) averaged 50% of the landscape in all area-years.