. The Canadian field-naturalist. Natural history. 2001 Schmutz, Houston, and Barry: Decline Among Swainson's Hawks 269 Plots o o o o i- C\J CO 40 n 30 - CM E o 2 20- CO â M 0) 10 - survey. Yolo County E Calif. D a Hanna, AB D â high Butte V. CA E 1 med. San Joaquin ca m | 9 low Colo. âi â 1 ' 1 â 1â 200 400 600 800 Size of Study Area (km2) L SE Idaho y/-zy 1000 2300 Figure 8. Swainson's Hawk densities based on study area size at Hanna (high, medium and low, Table 2), on the 1992 41-km2 survey plots in SE Alberta (mean = nests/100 km2), and on a township in the Kindersley, Saskatchewan
. The Canadian field-naturalist. Natural history. 2001 Schmutz, Houston, and Barry: Decline Among Swainson's Hawks 269 Plots o o o o i- C\J CO 40 n 30 - CM E o 2 20- CO â M 0) 10 - survey. Yolo County E Calif. D a Hanna, AB D â high Butte V. CA E 1 med. San Joaquin ca m | 9 low Colo. âi â 1 ' 1 â 1â 200 400 600 800 Size of Study Area (km2) L SE Idaho y/-zy 1000 2300 Figure 8. Swainson's Hawk densities based on study area size at Hanna (high, medium and low, Table 2), on the 1992 41-km2 survey plots in SE Alberta (mean = nests/100 km2), and on a township in the Kindersley, Saskatchewan area are compared to other recent studies: North Dakota (3 years; Igl and Johnson 1997), Pinion Canyon, Colorado (4 years; Anderson 1995; SE New Mexico (3 years; Bednarz 1988; SE Idaho (3 years; Hansen and Flake 1995); Yolo County (5 years) and San Joaquin Valley (3 years), California, England et al. 1995; Butte Valley, California, (4 years; Woodbridge et al. 1995). bird prey are now mature and some already have departed during the dry late summer. Insects, in con- trast, are at their peak in August. Hawk densities In comparison with other parts of the species' range (southeastern Idaho, Hansen and Flake, 1995; south- eastern Colorado, Andersen 1995; southeastern New Mexico, Bednarz 1988; Butte Valley, California, Woodbridge et al. 1995; Yolo Valley and San Joaquin Valley, California, England et al. 1995), our hawk densities are only slightly higher than average (Figure 8). The southeastern Alberta survey and that of Igl et al. (1999) in North Dakota may be the only studies where Swainson's Hawk population totals can be reli- ably extrapolated from samples representing and , respectively, of these two large regions. Swainson's Hawks have adjusted remarkably well to cereal crop production, especially where a moder- ate mix of habitat persists. Our earlier analyses showed that Swainson's Hawk densities are higher on plots with >30% cultivation than on plots wi
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