In recent years much emphasis has been placed on the conservation of raptors, which are generally low in numbers and tend to be highly sensitive to human activities such as shooting, pesticide use and habitat alteration (for a review see Newton 1979). Although the alteration and destruction of breeding habitat may currently be the greatest detriment to many bird species, the work of Fretwell (1977) on Dickcissels (Spiza americana) suggests that the loss of wintering habitat may, in some cases, be equally important. However, this aspect of raptor research has received comparatively little attention.
In 1981 we initiated a 2-year fall and winter study of raptors in the San Jacinto Valley to provide baseline data on populations in southern California and to quantify the importance of this valley as a wintering area for raptors.