Global Short Term Trend: Decline of 10-30%
Comments: Trends in Latin America unknown. Numbers of swifts in Oregon forests declined significantly in the 1980s (-8.9% annual change) (Sharp 1992). North American Breeding Bird Survey data (Sauer et al. 2000) are problematical because of low sample sizes. However, BBS data indicate a survey-wide decline from 1980 to 1999 (-4.2% average annual decline; P = 0.07; N = 122 survey routes). Mapped BBS trends show centers of long-term decline in British Columbia, western Washington, and northern California. BBS data are most robust for Washington State, where a significant and steep decline is evident from 1980-1999 (-8.7% average annual decrease; P = 0.01; N = 31). BBS data for 1980-1999 also show a nonsignificant increase in Oregon (2.9% average annual increase; P = 0.58; N = 45), and nonsignificant declines in California (-2.1% annually; P = 0.46; N=17) and British Columbia (-5.5% annually; P = 0.35; N = 18). Sample sizes in Idaho and Montana are too small for adequate trend analysis.
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