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Duck Nest Success in the Prairie Potholes


by
Terry L. Shaffer
National Biological Service
Wesley E. Newton
National Biological Service
Since the early 1970's, the numbers of some waterfowl species such as mallard (Anas platyrhynchos), blue-winged teal (A. discors), and northern pintail (A. acuta) have reached or nearly reached the lowest ever recorded. Low nest success (the proportion of nests in which one or more eggs hatch) in key breeding areas, including the U.S. Prairie Pothole region, is partly responsible for declines in duck numbers (Klett et al. 1988; Johnson et al. 1992).

Methods
Fig. 1. Areas of the Prairie Pothole region and time periods for which estimates of duck nest success were made. See Fig. 2 for abbreviations.
We examined status and trends of duck nest success for mallard, blue-winged teal, gadwall (A. strepera), northern shoveler (A. clypeata), and northern pintail, for one to four time periods between 1966 and 1989, and for five regions in North and South Dakota and Minnesota (Fig. 1). Nest success data originated from numerous independent studies conducted throughout the region. Some data from 1966 to 1984 were previously analyzed by Klett et al. (1988). We followed the methods of Klett et al., except we considered one additional time period (1985-89) and one additional habitat (Conservation Reserve Program lands).

Nest Success
Mallard
Data for 4,093 mallard nests showed that their nest success ranged from 6% to 20% (Fig. 2). Only 3 of 14 nest success estimates reached or exceeded 15%, the level of nest success thought necessary to maintain mallard numbers at a stable level in central North Dakota (Cowardin et al. 1985). These three areas were central South Dakota (1966-74), eastern South Dakota (1985-89), and central North Dakota (1985-89).

Fig. 2. Nest success (%) by period for five areas in the Prairie Pothole region for five duck species. Dashed line = level of nest success believed necessary for a stable population.
Mallard nest success was relatively steady from 1966-74 to 1980-84, but increased from 1980-84 to 1985-89. In 1985-89, mallard nest success was still less than 15% in two of four regions where data were available. Predation was the major cause of nest failure, accounting for 85% of mallard nest failures in North Dakota.
Blue-winged Teal
Data for 9,819 blue-winged teal nests revealed that nest success of blue-winged teal ranged from 12% to 29% (Fig. 2). The level of nest success needed to maintain stable numbers of blue-winged teal is believed to be 20% (Klett et al. 1988). Nest success of blue-winged teal was generally below this level, except in South Dakota.
Nest success increased slightly from 1980-84 to 1985-89, but was still generally less than 20%. Predation, the principal cause of blue-winged teal nest failures, accounted for 92% of the failed nests in North Dakota.
Gadwall
Data on 3,782 gadwall nests showed that their average nest success ranged from 11% in western Minnesota (1980-84) to 26% in central South Dakota (1966-74; Fig. 2). Nest success was generally below 20%, the minimum level believed necessary to sustain populations (Klett et al. 1988).
Gadwall nest success increased from 1980-84 to 1985-89 and reached or exceeded 20% during 1985-89 in North and South Dakota. Predation was the primary cause of nest failure, accounting for 90% of failed gadwall nests in North Dakota.
Northern Shoveler
Nest success in 1,212 shoveler nests ranged from 5% in western Minnesota (1980-84) to 35% in central South Dakota (1966-74; Fig. 2). Nest success was generally below 20%, the minimum level believed necessary to sustain populations (Klett et al. 1988). In western Minnesota and eastern North Dakota, nest success was less than 10%, but it was greater than 20% in central North and South Dakota.
Shoveler nest success increased from 1980-84 to 1985-89, but was still much less than 20% in western Minnesota and eastern North Dakota. Predation was the primary cause of nest failure in all regions, and in North Dakota caused 88% of shoveler nest failures.
Northern Pintail
Data for 1,633 pintail nests revealed that their success ranged from 5% to 20% (Fig. 2). Fifteen percent is the minimum level of nest success believed necessary to sustain pintail numbers (Klett et al. 1988). Only 2 of 14 nest success estimates reached or exceeded 15%; these were for central South Dakota (1966-74) and central North Dakota (1985-89).
Within each region, pintail nest success was generally lowest in 1966-74 and highest in 1985-89. Even in 1985-89, however, nest success was much less than 15% in all regions where data were available, except central North Dakota. Predation was the major cause of nest failure; for example, in North Dakota it accounted for 81% of pintail nest failures. In addition, because pintails nest more frequently in cropland than other species (Klett et al. 1988), farming operations were also an important cause of nest failure, accounting for 16% of pintail nest failures.

Trends
Our results suggest that nest success of the five species of ducks considered here was and probably still is too low to maintain stable numbers of breeding ducks in most areas of the Prairie Pothole region. For example, even though nest success increased from 1980-84 to 1985-89, it was still below the level needed to sustain populations for most species in most regions. Except for pintails, whose nest success generally increased, we observed no consistent increases or decreases in nest success across periods. In central South Dakota in the 1966-74 period nest success was much higher than in other regions, exceeding the level needed to sustain populations. This region likely contributed a "surplus" of ducks in 1966-74 that helped make up for the "shortage" of ducks produced in other regions. Unfortunately, no data for central South Dakota have been available since then.
Predation was the primary reason for the low nest success we observed. Predator species such as red fox (Vulpes vulpes), striped skunk (Mephitis mephitis), and raccoon (Procyon lotor) are common or numerous throughout the region (Sargeant et al. 1993). Both red foxes and striped skunks are important predators of duck nests (Johnson et al. 1989), and red foxes also take many female ducks during the breeding season (Sargeant et al. 1984).
More than two-thirds of the Prairie Pothole region is in Canada. Greenwood et al. (1987) studied mallard nest success in that portion of the region from 1982 to 1985. Their findings were similar to ours: mallard nest success averaged 12% and only 7 of 31 estimates on individual areas reached or exceeded 15%. Predators caused most nest failures. The authors concluded that nest success in much of Prairie Canada in 1982-85 was too low to maintain stable numbers of breeding mallards.
The status of duck nest success in the recent past in the Prairie Pothole region seems clear. Nest success was too low for duck populations to sustain themselves. Unless steps are taken to improve duck nest success in the future, we will likely see further declines in numbers of these and possibly other waterfowl species.
For further information:
Terry L. Shaffer
National Biological Service
Northern Prairie Science Center
8711 37th St. SE
Jamestown, ND 58401
References
Cowardin, L.M., D.S. Gilmer, and C.W. Shaiffer. 1985. Mallard recruitment in the agricultural environment of North Dakota. Wildlife Monographs 92. 37 pp.

Greenwood, R.J., A.B. Sargeant, D.H. Johnson, L.M. Cowardin, and T.L. Shaffer. 1987. Mallard nest success and recruitment in Prairie Canada. Transactions of the North American Wildlife and Natural Resources Conference 52:298-309.

Johnson, D.H., J.D. Nichols, and M.D. Schwartz. 1992. Population dynamics of breeding waterfowl. Pages 446-485 in B.D.J. Batt, ed. The ecology and management of breeding waterfowl. University of Minnesota Press, Minneapolis.

 Johnson, D.H., A.B. Sargeant, and R.J. Greenwood. 1989. Importance of individual species of predators on nesting success of ducks in the Canadian Prairie Pothole region. Canadian Journal of Zoology 67:291-297.

Klett, A.T., T.L. Shaffer, and D.H. Johnson. 1988. Duck nest success in the Prairie Pothole region. Journal of Wildlife Management 52(3):431-440.

Sargeant, A.B., S.H. Allen, and R.T. Eberhardt. 1984. Red fox predation on breeding ducks in midcontinent North America. Wildlife Monographs 89. 41 pp.

Sargeant, A.B., R.J. Greenwood, M.A. Sovada, and T.L. Shaffer. 1993. Distribution and abundance of predators that affect duck production--Prairie Pothole region. U.S. Fish and Wildlife Service Resour. Publ. 194. 96 pp.


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