Northern Prairie Wildlife Research Center
|Table 1. Availability (%) of 8 nesting habitats for mallard, gadwall, blue-winged teal, northern shoveler, and northern pintail by region and period.|
|Period||Cropland||Hayland||Grassland||Idle grassland||Planted cover||Right-of-way||Wetland||Odd area|
|Minn. west (MNW)|
|N.D. east (NDE)|
|N.D. central (NDC)|
|S.D. east (SDE)|
|S.D. central (SDC)|
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.
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|
|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.|
|Minn. west (MNW)|
|N.D. east (NDE)|
|N.D. central (NDC)|
|S.D. east (SDE)|
|S.D. central (SDC)|
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.|
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 (%)|
|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.