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4.7 BIOLOGICAL RESOURCES This migratory species winters in Argentina and then flies to the northern portion of the Central Valley to breed. In the west it prefers groves or small stands of mature oak, cottonwood, and other large foothill woodland trees as nest sites. One other criteria for such sites in California is that they receive little or no human disturbance during the nesting period. Several Swainson's hawks were regularly seen on the project site during April, and on May 7 the first nest was sighted. It was situated near the top of a tall Fremont cottonwood in Brovelli Woods at the eastern end of the proposed 13th fairway and the Mokelumne River (Figures 4.7-1,4.7-11 and 4.7-12). Swainson's Hawk have several color phases, and the pair which occupied this nest consisted of a light brown male and a dark brown-black female. This combination of plumage colors enabled recognition of this pair throughout the nesting period. On June 13, 1992, a downy gray chick was seen for the first time at the edge of the nest. It had been hatched at least a week before, but because all observations were made from a minimum of 100 yards away and from the cover of dense brush,detection of a chick could not be made until it was large enough to appear above the nest edge. By the end of June the single chick was fully feathered, and during the second week of July it and the two parent birds left the nest site. On May 31 a second nest was discovered in an isolated clump of oak trees near the site entrance(Figures 4.7-1, 4.7-9 and 4.7-13). A light brown female was sitting on the nest, indicating that eggs may be present. She was attended by a light brown male with a distinctive dark breast streak that also made ongoing identification of this pair possible. They occupied the nest site through the second week of June then it was deserted. During this two-week period the only observed disturbances were occasional vehicles coming onto the property and passing near the nest tree enroute to the lake areas. However,one or more disturbances may have occurred near the nest site between visits by the observation team to cause desertion of the nest. In addition to these two nesting pairs, four additional distinctly colored Swainson's hawks were seen on the project site during the survey period. On three occasions individuals were observed swooping to the ground after what was assumed to be rodent prey, but no kill was ever documented. Specimens were also seen flying to and from the site and the adjacent irrigated pasture areas where it was assumed they were also foraging. The most abundant raptor observed was the red-tailed hawk (Buteo jamaicensis). This is the only permanent resident soaring-type(buteo)hawk, and at least six individual specimens were seen on each visit to the site. Other raptors viewed one or more times were the northern harrier (Circus cyaneus), black-shouldered kite (Elanus caeruleus), Cooper's hawk(Accipiter cooperii), American kestral (Falco sparverius), great horned owl (Bubo virginianus), barn owl (7yto alba), and turkey vulture (Cathartes aura). The latter is in especially high numbers on the site which was once acclaimed to support the largest nesting colony of these birds in North America. 4.7-16