Vegetation of tropical dry ecosystems is represented by patches of plants with different photosynthetic pathways. We used C and N stable isotope mixing models to assess the relative importance of CAM and C3 vegetation as direct or indirect sources of food for birds in a Neotropical semiarid zone. We analyzed tissues from 26 bird species encompassing a broad array of feeding habits in the dry and rainy seasons. Although CAM plants are important elements of our study site, their use as food was mainly restricted to some plant-eating and omnivorous bird species. “Intermediate” or “High” dependence on CAM food was observed in only 7 species: three frugivores, one nectarivore, one granivore, and two omnivores. Instead, C3-derived food sustained most of the bird species studied, even some for which dependence on CAM-derived food was reported in studies using other methodological approaches. Consumption of C3 insects extended to the entire assemblage of birds, including plant-eating species. Our findings highlight the importance of maintaining vegetation heterogeneity in arid zones for animal communities and the need to provide increasing protection measures to woody C3 species, as their local demand for firewood is rapidly increasing. Abstract in Spanish is available with online material.