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Duck Nest Success in the Prairie Pothole Region

Results


Cropland composed most of the available habitat in all regions except SDC (Table 1). The percent of cropland was greatest in MNW and NDE. Grassland was the most available habitat in SDC, a major component in NDC and SDE, and least available in MNW and NDE. Each of the other habitats composed <5% of the available habitat in all regions except in MNW, where odd area, including woodland, made up about 9%. Idle grassland composed <1% of all available habitats in all regions.

Table 1.  Availability (%) of 8 nesting habitats for mallard, gadwall, blue-winged teal, northern shoveler, and northern pintail by region and period.
Region
Period Cropland Hayland Grassland Idle grassland Planted cover Right-of-way Wetland Odd area
Minn. west (MNW)
1980-84 77.5 2.8 5.5 0.1 0.6 2.3 2.5 8.8
N.D. east (NDE)
1966-74 77.3 2.5 7.5 0.1 2.4 2.1 4.0 4.0
1975-79 79.7 2.5 6.9 0.3 0.7 2.1 3.8 4.0
1980-84 79.8 2.5 6.7 0.4 0.7 2.1 3.7 4.0
N.D. central (NDC)
1966-74 57.0 3.4 29.7 0.4 2.0 1.2 4.8 1.6
1975-79 60.2 3.4 27.7 0.7 0.6 1.2 4.6 1.6
1980-84 60.8 3.4 27.2 0.7 0.6 1.2 4.4 1.6
S.D. east (SDE)
   1966-74 54.7 2.9 30.9 <0.1 2.0 1.8 4.2 3.5
1980-84 58.6 2.9 28.6 0.2 0.5 1.8 3.8 3.5
S.D. central (SDC)
1966-74 42.1 4.8 46.2 <0.1 1.4 1.1 3.3 1.2

The composition of available nesting habitats was compared among 3 periods in NDE and NDC and between 2 periods in SDE. The most important change in habitat composition was the loss of planted cover that occurred after 1966-74 as a result of the expiration of cropland retirement programs. Conversion of planted cover, grassland, and wetland to cropland during 1975-79 resulted in slight increases (<4 %) in the availability of cropland.

Nesting Results

Species Accounts.--The nesting habitat most preferred by mallards was planted cover; odd area ranked second and cropland was the least preferred (Table 2). Mallard nest success was highest in SDC, intermediate in NDC and SDE, and lowest in MNW and NDE (Table 3). Success did not vary appreciably among periods. Mallards had the greatest success in all periods in idle grassland; the habitat ranked second was planted cover in 1966-74, grassland in 1975-79, and wetland in 1980-84 (Table 4). Mallards were least successful in cropland followed by hayland, odd area, and right-of-way. Predation was the principal cause of nest failure for mallards and all other duck species studied (Table 5).

Table 2.  Relative preference of mallard, gadwall, blue-winged teal, northern shoveler, and northern pintail for 8 classes of nesting habitat in central North Dakota.
Habitat Mallard Gadwall Blue-winged teal Northern shoveler Northern pintail
Cropland 0.3a 0.2 0.3 0.2 5.4
Hayland 10.7 13.1 8.4 6.8 14.2
Grassland 4.5 6.7 11.8 10.0 8.5
Idle grassland 6.7 4.9 4.9 3.0 2.8
Planted cover 42.8 43.0 39.1 45.2 43.5
Right-of-way 7.6 6.0 6.7 8.4 9.1
Wetland 9.7 12.7 12.9 12.1 6.8
Odd area 17.7 13.4 15.9 14.3 9.7
a Preference of a species for a habitat is the probability that a F will select that habitat for nesting, given that all habitats are equally available.

Preferences of gadwalls for nesting habitats were similar to those of mallards (Table 2). Nest success of gadwalls was about 2x that of mallards except in SDC, where it was about 30% higher (Table 3). Regional differences in gadwall nest success were similar to those of mallards. Gadwalls were most successful in cropland and idle grassland (Table 4). Gadwalls were more successful than mallards in all habitats except idle grassland, where success was similar to that of mallards. Gadwalls nesting in hayland, right-of-way, and wetland were least successful.

Table 3.  Estimated percent nest success (n = no. nests) of mallard, gadwall, blue-winged teal, northern shoveler, and northern pintail by region and period.
  Mallard Gadwall Blue-winged teal Shoveler Pintail
Region
Period % n % n % n % n % n
Minn. west (MNW)
1980-84 5 90 10 13 16 620 1 11 6 13
N.D. east (NDE)
1966-74 5 46 9 52 10 216 5 12 5 54
1975-79 5 158 12 174 13 444 7 92 6 184
1980-84 5 20 11 19 12 94 5 6 7 6
N.D. central (NDC)
1966-74 8 210 14 373 12 1,010 16 82 9 162
1975-79 11 1,036 21 979 20 2,449 26 411 13 503
1980-84 10 929 18 907 16 1,180 19 268 13 310
S.D. east (SDE)
1966-74 9 51 19 72 21 393 12 14 3 10
1980-84 10 79 23 52 27 382 15 21 5 27
S.D. central (SDC)
1966-74 19 487 25 386 29 378 36 69 19 122

Blue-winged teal also preferred planted cover over other habitat classes (Table 2). Blue-winged teal were more selective for grassland than mallards, gadwalls, and pintails. Cropland was least preferred. Nest success of blue-winged teal was similar to that of gadwall except in MNW, where it was 60% higher (Table 3). Success was highest in SDE and SDC and lowest in NDE. Among habitats, success was lowest in cropland and varied little among the other 7 habitats (Table 4).

Table 4.  Estimated percent nest success, number of nests (n), and percent of nest initiations (I) by habitat for mallard, gadwall, blue-winged teal, northern shoveler, and northern pintail in North Dakota, 1966-84.
  Mallard Gadwall Blue-winged teal Shoveler Pintail
Habitat
Period % n I % n I % n I % n I % n I
Cropland
1966-74 1 5 7 20 6 3 6 26 5 7 3 3 5 53 51
1975-79 2 10 9 24 0 4 7 1 6 9 6 4 6 27 57
1980-84 3 4 9 41 1 4 12 6 6 15 0 4 11 27 57
Hayland
1966-74 2 0 9 3 1 10 7 4 5 2 0 5 2 0 6
1975-79 4 31 12 6 20 13 13 29 7 4 3 6 3 10 6
1980-84 6 11 12 8 27 13 18 25 7 6 12 6 4 12 6
Grassland
1966-74 6 17 23 12 53 31 11 233 43 14 11 39 10 16 21
1975-79 12 116 27 23 96 35 21 524 48 27 72 46 19 70 21
1980-84 8 76 26 15 127 35 14 201 47 18 63 46 13 69 21
Idle grassland
1966-74 18 59 <1 18 142 <1 11 469 <1 16 35 <1 18 30 <1
1975-79 27 253 1 26 230 1 17 480 1 22 42 <1 27 66 <1
1980-84 27 466 1 27 313 1 17 437 1 22 69 <1 27 89 <1
Planted cover
1966-74 10 156 28 14 202 26 13 405 20 12 41 25 10 105 13
1975-79 10 660 11 13 740 10 13 1,608 7 12 336 9 10 454 4
1980-84 9 272 11 12 377 11 12 482 8 11 96 10 9 97 5
Right-of-way
1966-74 4 11 4 7 12 3 11 24 3 6 3 4 6 5 2
1975-79 5 63 5 10 39 4 15 148 3 9 33 5 9 45 2
1980-84 5 57 5 9 31 4 13 50 3 8 13 5 8 8 2
Wetland
1966-74 7 2 13 10 4 15 11 44 13 3 0 13 5 6 4
1975-79 7 20 15 9 8 18 10 43 14 3 4 15 5 2 4
1980-84 12 37 15 16 28 18 17 51 14 5 14 15 8 8 4
Odd area
1966-74 5 6 16 17 5 11 14 21 11 9 1 11 6 1 4
1975-79 5 41 20 18 20 15 15 60 14 10 7 14 7 13 4
1980-84 3 26 20 12 22 15 10 22 14 7 7 14 5 6 4
Total
1966-74 6 256 100 12 425 100 11 1,226 100 10 94 100 7 216 100
1975-79 8 1,194 100 16 1,153 100 17 2,893 100 16 503 100 9 687 100
1980-84 7 949 100 15 926 100 14 1,274 100 13 274 100 10 316 100

Nesting habitat preferences of shovelers were similar to those of blue-winged teal (Table 2). Nest success of shovelers was low and comparable to that of mallards in MNW, NDE, and SDE (Table 3). In NDC and SDC, success of shovelers was higher than for any other species. Shovelers were most successful in grassland and idle grassland and least successful in hayland and wetland (Table 4).

Preferred habitat of the pintail was planted cover; hayland ranked second and idle grassland was the least preferred (Table 2). The preference of pintails for cropland was greater than that of the other species. Preference for cropland, although lower than for most other habitats, is important because cropland is highly available. Among regions, nest success rates for pintails were generally low and comparable to those of mallards (Table 3). Success was somewhat higher for pintails than for mallards in cropland and grassland (Table 4). Nest success in other habitats was similar for both species. In addition to predation, destruction by farm machinery also was an important cause of pintail-nest loss (Table 5).

Table 5.  Outcomes of nesting attempts by 5 species of ducks and in 8 habitats in North Dakota, 1966-84.
  Successful (%) Unsuccessful (%)
Predation Machines Othera
Species
    Mallard 7 82 7 4
    Gadwall 13 77 5 4
    Blue-winged teal 13 78 4 4
    Northern shoveler 12 79 4 5
    Northern pintail 8 67 22 3
Habitat
    Cropland 7 54 37 3
    Hayland 6 66 27 2
    Grassland 14 81 <1 5
    Idle Grassland 21 76 <1 3
    Planted cover 12 85 <1 3
    Right-of-way 8 81 5 6
    Wetland 9 81 2 8
    Odd Area 10 83 3 4
All habitats and species 11 77 8 4
aOther includes weather, fire, livestock, and unknown.

Regional and Temporal Differences in Nest Success.--Our results suggest the following regional gradient in nest success (from lowest to highest): (1) MNW and NDE, (2) NDC, (3) SDE, (4) SDC (Table 3). Important exceptions were that nest success rates for blue-winged teal in MNW were similar to those in NDC, rates for pintails in SDE were similar to those in MNW, and rates for shovelers in SDE were lower than in NDC.

In regions where comparable data were available, nest success for gadwalls, blue-winged teal, and shovelers tended to be lowest in 1966-74 and highest in 1975-79; this trend was most evident in NDC (Table 3). Differences among periods were small for mallards and pintails.

Nesting Results by Habitat.--We combined data from NDE and NDC to illustrate differences in nesting success among habitats. Samples in these 2 regions were larger and had better spatial and temporal distributions than the other regions.

Cropland was the most common habitat (Table 1) but the least preferred for nesting by all species except pintail (Table 2). The relative preference of nesting pintails for cropland was about 5% compared with <0.5% for the other species. Cropland was also the most important nesting habitat for pintails; 51-57% of their nests were located there (Table 4). Cropland accounted for <10% of the nests initiated by the other species. Nests of blue-winged teal (n = 33) and pintails (n = 107) made up 80% of all nests found in cropland. Nest success of these 2 species in cropland ranged from 5 to 12% (Table 4). Nest success of mallards in cropland was <5% in all periods. Success rates for gadwalls and shovelers were derived from small samples and may not be meaningful. Most of the nest losses occurring in cropland were caused by predation or farming operations (Table 5).

Hayland composed 3% of the available nesting cover. Roughly 10% of the nest initiations of mallards and gadwalls but <8% of those of the other species were in hayland (Table 4). Nest success of mallards, gadwalls, shovelers, and pintails was always <10% and most often <5% (Table 4). Blue-winged teal were more successful in hayland than the other 4 species. Most nest losses were caused by predation but losses caused by haying operations were also important (Table 5).

Grassland was the second most available nesting habitat (Table 1). In most periods, mallards, gadwalls, blue-winged teal, and shovelers initiated more nests in grassland than any other habitat. Use of grassland by nesting pintails ranked second after cropland (Table 4). Nest success in grassland was above average for shovelers and pintails and about average for the other species.

Less than 2% of all nest initiations occurred in idle grassland (Table 4), reflecting its scarcity (Table 1) and low preference value (Table 2). Nest success of all species was comparatively high in idle grassland.

Planted cover was the nesting habitat most preferred by all species (Table 2), but like idle grassland it composed a small part of the available habitat (Table 1). During 1966-74, approximately 25% of all mallard, gadwall, and shoveler nests were initiated in planted cover (Table 4). The importance of planted cover to nesting ducks declined when it became less available after 1966-74. In comparison to other habitats, nest success in planted cover was about average and was fairly stable throughout all periods.

Relatively few nests were initiated in right-of-way (Table 4) because of its scarcity (Table 1). Nest success in right-of-way was generally low compared to that in other habitats (Table 4).

The availability of wetland ranked third after cropland and grassland (Table 1). Fewer than 5% of all pintail nests were initiated in wetland; initiations by the other species ranged from 13 to 18% (Table 4). Compared with other habitats, nest success in wetland was about average for mallards, gadwalls, and blue-winged teal but below average for shovelers and pintails (Table 4). Estimates of nest initiations and nest success were biased because most of the nest searches were conducted in the wet meadow zone, hence, few overwater nests are included in the sample. The bias would affect species estimates differently. Of the species studied, the mallard is the most prone to nest overwater (Evans and Black 1956:39, Jessen et al. 1964:59).

Odd area composed only 3% of the available habitat (Table 1) but >10% of nest initiations for all species except pintail were in this habitat (Table 4). Nest success rates were fairly consistent among periods, but were generally average to below average, depending on the species.


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