Long-term studies of bird populations in California mountains are conspicuously absent from the literature. While distribution of summer resident species is generally well known, population changes through the summer and fall need study. This is certainly the case in the Yolla Bolly Mountains of the interior north coast ranges of California. Hemphill (1952) presents a fairly complete account of species occurrence in the southern Yolla Bolly Mountains during the summer. A banding project carried out in the Yolla Bollys 15 June to 6 October 1973 afforded us the opportunity to observe seasonal changes in bird populations. This paper is a summary of data collected on a closely interrelated group of species, the wood warblers (Parulidae).