Roadside raptor surveys have historically been used to establish indices of relative abundance of wintering raptors. This research establishes baseline data for migratory wintering raptors in the central San Joaquin Valley and compares these findings with surveys conducted after 1970. Survey routes of 62-, 82-, and 86-km were chosen that traveled across Fresno, Madera, and Merced counties. All raptors within 0.5 km of each side of the road were identified using binoculars and a 20X spotting scope. Data collected was used to estimate population size and relative abundance of each raptor species. Land use patterns since 1970 throughout the study area were determined using aerial photographs and land use maps. A significant increase in total acreage of orchards and vineyards and a significant decrease in total acreage of alfalfa and irrigated pasture occurred from 1970 to 1994. Changes in raptor abundance that may have been due to the changes in vegetation were observed Red-tailed hawk (Buteo jamaicensis) populations showed a significant increase in relative abundance from 28% to 48% (P < 0.05) while the indices for American kestrels (Falco sparverius)(48% to 40%) and northern harriers (Circus cyaneaus)(23% to 9%) declined significantly (P < 0.05). The populations of ferruginous hawks (Buteo regalis) and Swainson's hawks (Buteo swainsoni) showed no significant change in abundance.
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