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NESTING REQUIREMENTS <br /> Swainson's hawks nest throughout most of the floor of the <br /> Central Valley, although nesting habitat is fragmented and <br /> unevenly distributed. More than 85% of the known nests in the <br /> Central Valley are within riparian systems in Sacramento, Yolo, <br /> and San Joaquin Counties. 'Much of the potential nesting habitat <br /> remaining in this area is in riparian forests, lone 'trees, oak <br /> groves, and roadside trees. The riparian areas are generally <br /> adjacent to and within easy flying distance to alfalfa or hay <br /> fields. Department research has shown that valley oaks (Quercus <br /> lobata) ,. Fremont's cottonwood (Poplus fremontii) , willows (Salix <br /> spp. ) , sycamores (Platanus spp. ) , and walnut (Juglans spp. ) are <br /> the preferred nest trees for Swainson's hawks (Bloom 1980, Estep <br /> 1989) . <br /> FALL AND WINTER MIGRATION HABITATS <br /> During their annual fall and winter migration periods. <br /> Swainson's hawks may congregate in large groups (up to 100+ <br /> birds) Some of these sites may- be used during delayed migration <br /> periods lasting up to three months. Such sites have been <br /> identified in Yolo and San Joaquin Counties. Specific protection <br /> is needed for these areas and surrounding foraging areas. <br /> HISTORICAL AND CURRENT POPULATION STATUS <br /> The Swainson's Hawk was historically (ca 1900) regarded as <br /> one of the most common and numerous raptor species in the state, <br /> so much so that they were often not given special mention in <br /> field notes. The breeding population has declined by an <br /> estimated 91% in California since the turn of the century (Bloom <br /> 1980) . The historical Swainson's hawk population estimate, based <br /> on current densities and estimates of former available habitat, <br /> is 4 , 284 - 17 , 136 pairs (Bloom 1980) . In 1979 , approximately 375 <br /> +50 breeding pairs of Swainson's hawks were estimated in <br /> California, and 280 (75%) of those pairs were estimated to be in <br /> the Central Valley (Bloom 1980) . In 1988 , 241 active breeding <br /> pairs were found in the Central Valley, with an additional 78 <br /> active pairs known in northeastern California. The 1989 <br /> population estimate was 430 pairs for the Central Valley and 550 <br /> pairs statewide. This difference in population estimates reflect <br /> increased survey intensity, not an actual population increase. <br /> VI-17 <br />