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Factors Associated with Duck Nest Success
in the Prairie Pothole Region of Canada

Habitat


Habitat composition of study areas was determined by the National Wetland Inventory, USFWS, St. Petersburg, Florida, from color infrared aerial photographs (scale 1:24,000) obtained in May and July 1982. Habitat polygons were defined and data were digitized by means of the Wetland Analytical Mapping System software (Pywell and Niedzwiadek 1980) and converted to Map Overlay Statistical System files (Autometrics, Inc., Fort Collins, Colo., unpubl. rep.). The digitized data were used to create a color-coded habitat map and a text file containing the area and perimeter of each habitat polygon for each study area.

Classification

We categorized all habitats into the classes of Cowardin et al. (1988): Cropland, Wetland, Hayland, Woodland, Right-of-way, Odd area, and Barren. We replaced their class Grassland with 2 other classes, Grass and Brush, because brush is especially important to mallards for nesting (Cowardin et al. 1985). We defined Grass as untilled land >=2 ha dominated (>50% areal cover) by grasses and forbs. Brush was untilled land >=0.2 ha dominated (>50% areal cover) by woody vegetation <=1 m tall in Grass >=2 ha (usually native prairie). Wetland included all basins regardless of whether they were wet or dry. Odd area included areas of grasses and forbs <2 ha and an array of other 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). Barren was composed of areas not suitable for nesting (e.g., road surfaces); we considered areas classified as Barren to be unavailable for nesting. Mean percentages of all habitats in parkland and prairie were weighted by size of study areas.

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.

Composition

Table 2. Size (ha) of study areas in the Prairie Pothole Region of Canada and composition (%) of landscapes based on interpretation of aerial photography obtained in May and July 1982. Means were weighted by size of study area. Rows sum to 100% with rounding errors.
Study area Size (ha) Habitat (%)
Crop- land Grass Brush Wet- land Hay- land Wood- land Right- of-way Odd areaa Barrenb
Parkland
Earl Grey 2,638 80 1 <1 8 <1 0 2 8 1
Hanley 2,691 70 8 3 11 0 0 2 6 1
Hay Lakes 2,700 44 12 <1 16 12 5 3 8 1
Holden 2,658 45 24 <1 17 0 <1 3 9 1
Inchkeith 2,683 71 10 <1 5 0 <1 4 8 1
Leask 2,691 40 23 <1 12 3 12 3 7 1
Moore Park 2,729 62 7 <1 14 1 2 3 11 1
Penhold 2,677 50 19 0 19 2 3 2 5 1
Yorkton 2,708 45 22 <1 11 2 9 2 8 <1
Mean 2,686 56 16 1 13 2 4 3 8 1
Prairie
Cartwright 2,719 66 16 0 7 3 0 3 5 1
Ceylon 2,666 56 28 3 9 0 0 1 1 1
Craik 2,646 84 2 <1 7 0 0 2 3 1
Denzil 2,691 76 9 <1 7 0 0 3 4 1
Gayford 2,699 30 37 4 14 8 0 2 3 1
Goodwater 2,661 50 27 2 9 7 0 3 2 1
Shamrock 2,693 59 22 2 7 5 0 2 2 1
Tichfield 2,662 75 9 2 7 <1 <1 2 3 1
Mean 2,680 62 22 2 8 3 <1 2 3 1
Overall Mean 2,683 59 19 1 11 3 2 2 5 1
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.

Table 3. Amount of Cropland available (ha) and amount considered suitable (%) as nesting cover (uncultivated standing stubble) in the first week of May on study areas in the Prairie Pothole Region of Canada. Means were weighted by available Cropland.
Study area Cropland available (ha) Suitable for nesting (%)
1982 1983 1984 1985
Parkland
Earl Grey 2,102 - - - 41
Hanley 1,889 17 26 12 69
Hay Lakes 1,178 - 19 19 -
Holden 1,208 - 60 - -
Inchkeith 1,917 - - 29 26
Leask 1,068 - - 9 17
Moore Park 1,700 - 16 7 -
Penhold 1,342 - - 5 13
Yorkton 1,214 - - - 7
Mean 1,513 17 27 13 33
Prairie
Cartwright 1,786 - 13 - -
Ceylon 1,506 - 40 18 -
Craik 2,223 - - 24 50
Denzil 2,058 - - 17 55
Gayford 808 - - - 61
Goodwater 1,319 - 36 - -
Shamrock 1,585 45 32 29 44
Tichfield 2,009 72 - - -
Mean 1,662 35 29 22 51
Overall Mean 1,583 29 28 17 40

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).

Table 4. Estimated number of temporary (T), seasonal (S), and semipermanent (SP) wetlands (Cowardin et al. 1988) per km² on study areas in the Prairie Pothole Region of Canada and percentage that were wet in Maya. Means were weighted by estimated number of wetlands/km²
Study area Estimated no./km² Wet wetlands (%)
1982 1983 1984 1985
T S SP T S SP T S SP T S SP T S SP
Parkland
Earl Grey 19 14 6 - - - - - - - - - 74 97 100
Hanley 2 28 11 33 62 75 58 71 89 0 6 38 75 91 97
Hay Lakes 9 8 12 - - - 40 61 89 18 35 78 - - -
Holden 4 8 5 - - - 35 46 97 - - - - - -
Inchkeith 18 4 2 - - - - - - 6 43 91 67 93 100
Leask 6 1 3 - - - - - - 19 67 100 59 67 100
Moore Park 11 24 15 - - - 62 94 100 11 43 90 - - -
Penhold 1 10 5 - - - - - - 17 21 73 33 39 57
Yorkton 7 13 14 - - - - - - - - - 44 86 96
Mean 9 12 8 33 62 75 50 75 94 11 26 74 65 84 93
Prairie
Cartwright 1 13 3 - - - 33 70 94 - - - - - -
Ceylon 8 6 4 - - - 55 88 96 4 24 64 - - -
Craik 11 10 3 - - - - - - 1 14 83 80 86 100
Denzil 10 5 2 - - - - - - 41 66 87 75 97 92
Gayford 6 4 6 - - - - - - - - - 14 37 83
Goodwater 4 11 7 - - - 24 83 100 - - - - - -
Shamrock 4 9 7 28 80 98 35 84 98 0 2 44 3 20 76
Tichfield 12 9 4 53 92 100 - - - - - - - - -
Mean 7 8 5 47 86 99 42 80 98 14 21 62 58 60 84
Overall Mean 8 10 6 45 71 87 47 77 95 12 24 71 62 77 90
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.


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