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Differential Effects of Coyotes and Red Foxes
on Duck Nest Success

Introduction


Low nest success is an important factor affecting duck recruitment in the Prairie Pothole Region (PPR) (Cowardin and Johnson 1979, Greenwood et al. 1987, Johnson et al. 1987, Klett et al. 1988). Nest success of about 15% for mallard (Anas platyrhynchos) and northern pintail (A. acuta) and 20% for blue-winged teal (A. discors), gadwall (A. strepera), and northern shoveler (A. clypeata) has been estimated as necessary for population stability in these species (Cowardin et al. 1985, Klett et al. 1988). Nest success of dabbling ducks in much of the PPR is less than those estimates (Cowardin et al. 1985, Greenwood et al. 1987, Klett et al. 1988). Predation accounts for >70% of these nest failures (Cowardin et al. 1985, Greenwood et al. 1987, Klett et al. 1988).

The red fox is a particularly severe predator of nesting ducks and duck clutches in uplands (Sargeant 1972, Johnson and Sargeant 1977, Johnson et al. 1989). Coyotes also prey on nesting ducks and their clutches (Sooter 1946, Keith 1961, Dzubin and Gollop 1972), but are believed to be less detrimental to duck production than are foxes (Johnson et al. 1989). Coyotes and red foxes are territorial, but in sympatric populations, coyotes exclude foxes (Sargeant 1982, Voigt and Earle 1983, Major and Sherburne 1987, Sargeant et al. 1987, Harrison et al. 1989, Sargeant et al. 1993).

Fox abundance increased in the eastern half of the PPR after the 1930s, following a decline in coyote abundance (Sargeant 1982). Since the mid-1970s, however, coyote populations in North Dakota and South Dakota have expanded following restrictions in methods of fur harvest and animal control (e.g., curtailment of aerial hunting and use of predicides) and the lower commercial value of fur. Coincidentally, fox abundance declined in areas reoccupied by coyotes (Sovada 1993). Changes in distribution and abundance of coyotes thus apparently affect potential depredations by foxes. We tested the hypothesis that presence of coyotes rather than foxes would result in higher duck nest success in uplands.

We thank K. M. Kraft, D. J. Rova, and T. L. Shaffer for data processing and statistical assistance; E. J. Clem, H. L. Johnson, S. A. Norland, J. M. Roaldson, S. J. Sovada, and E. K. Shanahan for field assistance; and S. H. Allen, R. J. Greenwood, and P. J. Pietz for comments on the manuscript.


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