DISTRIBUTION AND TRENDS IN ABUNDANCE OF ROUGH-LEGGED HAWKS WINTERING IN CALIFORNIA

Distribution and trends in abundance of Rough-legged Hawks (Buteo lago pus) wintering in California were assessed using Christmas Bird Counts (CBCs). Data from 114 individual CBCs conducted in California over 40 yr during the winters of 1949-1950 to 1988-1989 were used. The percen tage of CBCs with Rough-legged Hawks, average number of hawks/CBC, and average number of hawks/160 party-km/CBC were positively correlated w ith year (P < 0.0001) over the 40-yr period. The frequency distributio n of intervals between statewide population peaks differed significant ly (P < 0.001) from a random pattern, and was not significantly differ ent (P > 0.75) from a 4-yr cycle. These results indicated that the pea ks in wintering populations of Rough-legged Hawks are more cyclic than irregular. Rough-legged Hawk numbers were significantly (P < 0.001) d ifferent among eight geographic regions in California, and the greates t numbers of hawks were found in the North Interior and North and Sout h Sierra Nevada regions. Significant positive correlations (P < 0.05) were found for average number of hawks/CBC and average number of hawks /160 party-km/CBC with year in all geographic regions except the North Sierra (both variables) and Central Coast (average number/CBC).