. The Canadian field-naturalist. 58 62 66 70 74 78 82 54 58 62 66 70 74 78 82 86 b) slope= p= 54 58 62 66 70 74 78 82 86 d) 300 200- m 100 es 3 •O 0 w OS -100 -200 -300 slope= p= Vv\ 54 58 62 66 70 74 78 82 86 Figure 2. American Coot population trends calculated from various sources. Slopes and p values are from regression equations of coot numbers on time (a) or of residuals from coot harvest vs. number of hunters on time (b-c). a) Breeding Ground Survey transects in the prairie provinces; b) Canadian harvest; c) total harvest; d) Atlantic flyway harvest. mates correspo
. The Canadian field-naturalist. 58 62 66 70 74 78 82 54 58 62 66 70 74 78 82 86 b) slope= p= 54 58 62 66 70 74 78 82 86 d) 300 200- m 100 es 3 •O 0 w OS -100 -200 -300 slope= p= Vv\ 54 58 62 66 70 74 78 82 86 Figure 2. American Coot population trends calculated from various sources. Slopes and p values are from regression equations of coot numbers on time (a) or of residuals from coot harvest vs. number of hunters on time (b-c). a) Breeding Ground Survey transects in the prairie provinces; b) Canadian harvest; c) total harvest; d) Atlantic flyway harvest. mates correspond to drought years as calculated with the Palmer Drought Index (Atmospheric Environment Service data). Coot populations decline with decreasing water levels that result from drought (Weller et al. 1958; Krapu et al. 1970; Sutherland 1991) and production of young decreases dramatical- ly during droughts (Krapu et al. 1970; Sutherland 1991). Duck numbers on the prairies also correspond well to changing moisture levels (Boyd 1981; Jones 1984). Breeding Bird Survey data can be used to investi- gate population trends since 1966, 1967, or 1968, depending on the area (Droege and Sauer 1989). Because the data recorded consist of birds seen or heard from routes along all-weather roads, marsh species tend to be undercounted. The routes do not usually traverse wetlands and marsh birds are not easily detected because of poor visibility in dense vegetation. Coots, however, feed in open water and are relatively vocal during the breeding season, so where routes do pass wetlands they may be highly detectable. In fact, significant average numbers of coots per Breeding Bird Survey route were detected in the prairie provinces. Data on population trends of species of birds along Breeding Bird Survey routes were requested from the Fish and Wildlife Service. This agency calculates trends for states, provinces, regions of North America, all of Canada, all of the , and for physiographic st
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