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Distribution and Abundance of Predators that Affect
Duck Production: Prairie Pothole Region

Species Accounts -- Corvids

Black-billed Magpie

Habitat and History. The black-billed magpie is a western North American species (Robbins et al. 1983; Godfrey 1986) that lives primarily in wooded and tall brush habitats, including farmsteads (Bent 1964; Shaw 1967; Bock and Lepthien 1975). The history of this species is discussed by many investigators (N. Criddle 1923; Farley 1925, 1932; Linsdale 1937; Rand 1948a; Houston 1949; Bird 1961; Houston 1977; Callin 1980). From these accounts, we concluded black-billed magpies were widely distributed and common throughout most of the prairie pothole region where tall brush and trees were available for nesting during the 1800's. By the turn of the century, black-billed magpies had become scarce or absent in much of the region but then gradually increased, especially after 1920 (Taverner 1926). The increases resulted in extensive attempts to control the abundance of the species (Phillips 1928; Salt and Salt 1976). Nevertheless, by the 1960's the black-billed magpie was common to abundant throughout the prairie pothole region of Saskatchewan (Houston 1977) and in western North Dakota and South Dakota (Stewart 1975; South Dakota Ornithologists' Union 1991). Although settlement of the prairie pothole region was initially detrimental to the species, the species seems to have benefitted from subsequent activities such as development of farmsteads (Salt and Salt 1976).

Population Structure. Black-billed magpies tend to remain in the same area throughout the year and to live in loose colonies in which populations can build to high levels. Breeding densities of 24 and 28 birds/0.65 km2 have been reported in central Alberta and western Montana (Brown 1957; Shaw 1967).

Distribution and Abundance. Black-billed magpies were much more numerous in study areas in Canada than in the United States (Fig. 14). They were common or more abundant in a significantly greater percentage of study areas in Canada than in the United States (Appendix Table 6). In Canada, they were numerous in 1 study area (6%), common in 5 (31%), and uncommon in 10 (63%). In the United States, they were detected in only three study areas (18%) and were scarce or uncommon in each. Although searches for occupied nests were not included in our surveys, nests with eggs or young were recorded during ≥1 year in all except four study areas in Canada (Gayford, Ceylon, Goodwater, Shamrock; Appendix Table 12). Occupied nests may have been present in one of those areas (Gayford) where birds were occasionally seen and nests could easily have been overlooked but were probably not present in the other three study areas where few birds were seen and nests would have been conspicuous. Most found nests were in active or abandoned farmsteads. No occupied black-billed magpie nests were found in any study area in the United States, but scattered breeding populations occur in that portion of the prairie pothole region (Stewart 1975).

Differences in abundance of black-billed magpies among study areas were particularly evident in Canada (Fig. 14; Appendix Tables 4 and 12). There, populations were greater in the aspen parkland (detected in an average of 3.1% [SD = 2.09] of quarter sections per road-transect count) than in the prairie (detected in an average of 0.9% [SD = 1.04] of quarter sections per road-transect count; t = 2.5, 14 df, P = 0.025). Populations were also greater in the west (detected in an average of 5.0% [SD = 2.20] of quarter sections per road-transect count in Alberta) than in the east (detected in an average of 2.2% [SD = 1.37] of quarter sections per road-transect count in Manitoba and Saskatchewan combined; t = 2.4, 7 df, P = 0.047). Notable exceptions were an uncommon abundance in one study area (Leask in aspen parkland) with abundant brush and wooded habitat and a common abundance in one study area (Cartwright in prairie) near the eastern edge of the region (Fig. 14).

Fig. 14. Study areas in the prairie pothole region in which black-billed magpies were seen and occupied nests were found during annual surveys in the 1-3 years each area was studied (Appendix Tables 4,12, and 13), and ratings of the abundance of black-billed magpies in each area 1983-88.

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