The understory has received little attention in studies of tropical forest birds. However, the growing use of camera traps for the study of vertebrates such as mammals has prompted studies on the diversity of terrestrial birds or birds with limited flying capacity. In this study we present an analysis of the diversity of understory birds in a perennial tropical forest of the Chimalapas region, in southeastern Mexico. We collected 967 independent bird records comprising 10 orders, 15 families, 22 genera, and 27 species with a total sampling effort of 8,529 trap-days. The effective number of species indicated the presence of 31 species while Clench's species accumulation model indicated 32, suggesting that over 15% of the species remain to be recorded. Although we did not register all the species potentially present in the understory, bird diversity was higher than in other studies using camera traps. Crax rubra, Tinamus major, and Geotrygon montana were the most abundant species recorded. We obtained records for small-sized (Anthracothorax prevostii, Leptotila plumbeiceps, and Zentrygon albifacies) and migratory (Hylocichla mustelina) species, highlighting the potential of camera traps for their study.