Northern Prairie Wildlife Research Center
All carnivores in our surveys are known predators of adult ducks, duck eggs, or ducklings (Keith 1961; Teer 1964; Balser et al. 1968; Dzubin and Gollop 1972; Duebbert and Lokemoen 1976; Talent et al. 1983; Sargeant and Arnold 1984; Sargeant et al. 1984; Arnold and Fritzell 1987b; Fleskes 1988). Although three species of weasels are common in the region, we included only the ermine and long-tailed weasel in our surveys and did not distinguish between them. The third species, least weasel (Mustela nivalis), weighs less than 65 g and eats mice, voles, and other small prey (Banfield 1974; Jones et al. 1983). Whereas predation on waterfowl by the raccoon, striped skunk, and badger is almost exclusively on eggs, the other species also prey on adults and ducklings (Sargeant and Arnold 1984). We included the gray wolf in our species accounts because of its importance to understanding changes in canid populations in the region and because evidence of a resident gray wolf was found in one study area. Also, gray wolves prey on waterfowl and waterfowl eggs (Timm et al. 1975; Raveling and Lumsden 1977). The only other wild mammalian carnivores detected in our surveys were the black bear (Ursus americanus) and the river otter (Lutra canadensis). We excluded these from our species accounts because we had no evidence of resident individuals in any study area. A black bear was seen once in one study area (Lake Park) and tracks of a black bear were found once in 1 quarter section of another study area (Hawley), where also tracks of a river otter were found once.
The Franklin's ground squirrel is the only rodent believed to affect duck production in the prairie pothole region (Sowls 1948; Sargeant and Arnold 1984; Greenwood 1986; Sargeant et al. 1987b). Franklin's ground squirrels prey on duck eggs (Sargeant et al. 1987b) and occasionally kill ducklings (Sowls 1948).
The two species of corvids in our predator surveys (black-billed magpie and American crow) prey on waterfowl eggs (Kalmbach 1937; Williams and Marshall 1938; Sowls 1955; Anderson 1965; Jarvis and Harris 1971; Dzubin and Gollop 1972; Jones and Hungerford 1972). Both species also prey occasionally on ducklings (Linsdale 1937; Sowls 1955; Sutherland 1982). We included the common raven in our species accounts because it was regularly seen in one study area and preys on waterfowl eggs and young (Jarvis and Harris 1971). No other corvids are known to affect duck production in the prairie pothole region.
The five raptors treated in our species accounts are all relatively large, widely distributed, and at least locally common (Bent 1961; Robbins et al. 1983). Their diets consist primarily of small mammals and small birds, but include some ducks (McAtee 1935; Errington et al. 1940; Todd 1947; Hecht 1951; Houston 1960; Bent 1961; Luttich et al. 1970; McInvaille and Keith 1974; Dunkle 1977; Sherrod 1978; Blohm et al. 1980; Schmutz et al. 1980; Gilmer et al. 1983; Gilmer and Stewart 1983, 1984; Brace 1988). Raptors seldom prey on duck eggs, although northern harriers occasionally take unhatched and pipping eggs (Balser et al. 1968; Willms and Kreil 1984). Other raptors that could affect waterfowl production were either scarce in the few areas where they occurred (e.g., bald eagle [Haliaeetus leucocephalus], osprey [Pandion haliaetus], prairie falcon [Falco mexicanus], peregrine falcon [F. peregrinus]) or are migrants that seldom nest in the region (e.g., rough-legged hawk [Buteo lagopus]). The only other mid-size or larger raptor species known to be resident in any study areas were the Cooper's hawk (Accipiter cooperii), for which a single nest was found in one study area (Lake Park); broad-winged hawk (B. platypterus), for which a single nest was found in another study area (Yorkton); and long-eared owl (Asio otus) and short-eared owl (A. flammeus), both of which nested in several study areas.
We included two of three species of gulls that are common breeding residents in the prairie pothole region in our list of treated species even though we conducted no systematic surveys of the abundance of gulls. The large ring-billed gull and slightly larger California gull were included because both species, especially the California gull, occasionally prey on duck eggs and ducklings (Greenhalgh 1952; Odin 1957; Anderson 1965; Vermeer 1970; Duncan 1986) and incidental data revealed they were common or numerous in several study areas. The small Franklin's gull (Larus pipixcan) was excluded because it has not been implicated in predation on duck eggs or ducklings. Other species of gulls are occasionally seen in the region, but rarely nest there (Salt and Salt 1976; South Dakota Ornithologists' Union 1991).