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

Introduction


Populations of several species of dabbling ducks have declined in recent decades in North America. In the early 1980's, mallard (Anas platyrhynchos), blue-winged teal (A. discors), and northern pintail (A. acuta) breeding populations were near their lowest recorded levels since population surveys began in 1955 (Can Wildl. Serv. and U.S. Fish and Wildl. Serv. 1986, Johnson and Shaffer 1987, Reynolds et al. 1990). This prompted the Canadian Wildlife Service (CWS) and U.S. Fish and Wildlife Service (USFWS) in 1982 to initiate investigations of factors thought to influence duck populations in the Prairie Pothole Region (PPR) of Canada (Brace et al. 1987). As part of that investigation, we evaluated mallard nest success and recruitment (Greenwood et al. 1987). The present report focuses on the mallard, gadwall (A. strepera), blue-winged teal, northern shoveler (A. clypeata), and northern pintail (hereafter called the 5 common species), but also includes data on some other ducks.

The PPR of North America is the primary breeding ground for many ducks; about 80% of the Region is in Canada (Batt et al. 1989). Between 1955-85, an average of 21.6 million ducks used the PPR, representing about 51.1% of the total estimated surveyed population in the Continent. During those years, >50% of the mean total estimated breeding population of 8 of 12 species of ducks that breed in the PPR occurred there, including all 5 common species (Batt et al. 1989). Upland and wetland habitats important to nesting ducks changed considerably in the PPR of Canada after European settlers arrived (Bird 1961, Merriam 1978, Archibold and Wilson 1980). Lynch et al. (1963) estimated that 72% of land in the PPR of Canada produced cereal grains by the mid-1950'5. Nearly all the other upland is grazed by livestock.

Studies of nesting ducks conducted in the United States portion of the PPR before this study indicated that duck production was reduced because of low nest success. Cowardin et al. (1985) reported that mallard nest success averaged only 8% in central North Dakota during 1977-80 and concluded that this rate was insufficient to maintain the local breeding population without immigration. Klett et al. (1988) also concluded that nest success was too low for population stability of mallards, gadwalls, blue-winged teals, northern shovelers, and northern pintails in North Dakota, South Dakota, and Minnesota.

Numerous studies of nesting ducks have been conducted in the PPR of Canada (e.g., Milonski 1958, Keith 1961, Smith 1971, Stoudt 1971, Dwernychuk and Boag 1972, Dzubin and Gollop 1972, Fritzell 1975, Oetting and Dixon 1975, Calverley and Boag 1977, Hines and Mitchell 1983). Few, however, provided unbiased estimates of nest success (Johnson 1979) and none attempted to estimate nest success in all habitats at widely separated locations throughout the Region.

Our objectives were to estimate nest success of ducks, especially mallards, at widely separated locations in the PPR of Canada during 1982-85 and to describe primary causes of nest failure. In addition, we examined the relative importance of various components of the nesting process that are associated with mallard production.


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