Surveys of breeding birds in the remaining 20,000 ha of open space in the Puente-Chino Hills of southern California during spring and early summer 1997 and 1998 revealed several species declining or nearing extirpation in the Los Angeles area. This report represents the first treatment of the distribution of the birds of this fast-disappearing natural area. From data collected on point counts and transects, three areas appear in need of immediate conservation action for bird diversity in the Puente-Chino Hills to be maintained: the coastal sage scrub of northern Brea/Yorba Linda, the grassland of southern Rowland Heights, and the grassland of upper Tonner Canyon.