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The worth of the Tracy Lakes system to water birds lies in three aspects of their make up. Of greatest importance is that the shallow inshore areas of the lakes function as seasonal wetlands in which large amounts of annual seeds are produced after the water recedes in late spring. Such waters are inevitably more productive as winter feeding sites than permanent lakes. A second advantage that these lakes offer is their size. They afford the protection that small ponds cannot provide. Also, when a flock is disturbed at one end of a lake, it would inevitably fly only a short distance to the middle or other end, then slowly swim back toward its starting point. In contrast, small isolated ponds promote long, energy expending flights each time a flock is flushed from its surface. Finally, the lakes and adjacent Beaver Pond provide much needed nesting habitat for several key waterfowl species. Although the numbers of these observed in 1992 may not seem impressive, it should be remembered that this was apparently the first year since the beginning of the recent drought,six years ago, that the lakes have filled and then held water through the entire duckling rearing season. The significance of this lies in the fact that ducks, especially the females, tend to return to their juvenile habitat to breed as adults. Given the average life expectancy of 3-4 years for a wild duck on the Pacific Flyway, it is likely that most of the breeding pairs on the project site in 1992 simply wandered in by chance, since none were hatched as yet during the last (1985-86) full lake season. Following this breeding pattern, it can be assumed that a yearly increase in breeding pair numbers would occur in coming years as long as normal or above rainfall persists and/or lake levels are artificially maintained. A number of species listed in Appendix A are present on the site because of the unique old forest status of Brovelli Woods. This is especially true for species such as the tree swallow, plain titmouse, and assorted woodpeckers that must have old dead trees to provide hole nest sites. Of course, the presence of nesting wood ducks can also be attributed to this feature. Because of the continuous decrease of mature riparian woodland stands in San Joaquin and adjacent counties, any remaining substantial plots also function as a biological magnet for raptor species. This is especially true when these woodland stands are situated adjacent to good rodent habitat such as moderately grazed dry and irrigated pasture, such as that which occurs immediately to the north of the project site. This combination of roosting and nesting sites in mature foothill/riparian woodland,coupled with adjacent grassland foraging areas, is especially important for the Swainson's hawk (Buteo swainsoni), a migratory species listed as threatened by the State of California. 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. 14