Community organization of an oak woodland breeding avifauna was studied in Sonora, Mexico. Species were classified into guilds by quantifying foraging behavior, based on investigator-defined resource classes, and subjecting these data to cluster analysis. From this analysis five guilds were recognized: foliage gleaning, wood gleaning, wood probing, air sallying, and ground sallying. Within each resource class all guilds foraged in a significantly different manner, except for air and ground salliers. Species within guilds were most often separated by food-site and perch height. Use of height classes by the avian community was significantly different from the quantity of tree vegetation per height class. Differential height utilization generally resulted from gleaning and probing guilds foraging at upper heights and sallying guilds foraging at lower heights. Ecological separation within and among guilds is discussed and related to community organization in this oak woodland avifauna. When the guild structure of this community is compared to other oak woodland avifaunas, a decrease in foliage gleaners of nearly 2.5-fold and a 6.4-fold increase in salliers occur from Oregon to Sonora, Mexico. Utility of the guild approach is discussed in relation to some prominent questions raised by results of the above comparison concerning (1) foraging plasticity in species coexistence and (2) change in community structure over time and between geographic locations.