A community can be defined as a group of species that live in the same place, conected by feeding relationships and other interactions. One hypothesis used to explain community structure patterns is that of interspecific competition. Communities structured by competition must have a limit in terms of the similarity in resource utilization, which should guarantee the coexistence of the different species. The objectives of this study were: (1) to study and analyze the bird communities in the Cerrado biome of the Paranã river valley, GO and TO, especialy in dry forests; and (2) to test the similarity limiting hypothesis (MacArthur and Levins, 1967), that suggests that there is a maximum threshold in the morphological similarity among species, that is, in the associated use of resources. Mist nets were used in three areas of cerrado and in one of dry forest. A total of 734 individuals from 102 species were caught, as a result of 4879.5 net-hours. The highest species density in the dry forests of São Domingos, GO, were for the species: Basileuterus flaveolus, Dendrocolaptes platyrostris, Thamnophilus punctatus and Sittasomus griseicapillus. In the cerrado area, Alvorada do Norte, GO, the most abundant species were Columbina picui and C. squammata. In the cerrado of São Domingos, the highest species densities were for Amazilia fimbriata and T. punctatus and in the cerrado of Paranã, TO, A. fimbriata and Elaenia chiriquensis. The highest density index occurred for the Paranã cerrado community, and a higher occurrence of nectarivorous and frugivorous species was also recorded. In the dry forest fragments 134 birds were captured (this study and based upon Lopes (2004)). Of these, 72% are dependent upon forest habitats. Analyses show that the insectivorous, understory birds in the dry fores are ecologically and morphologically segregated in their morphometric space, and larger-bodied species with larger and longer beaks were separated from other species. The feeding categories of greater significance were Formicidae, Coleoptera, other Hymenoptera and Hemiptera. For the woodcreeper community we verified a higher ecological overlap between Dendrocolaptes platyrostris and Xiphorhynchus guttatus and between Lepidocolaptes angustirostris and Campylorhamphus trochilirostris. It is possible that between these paired species there occur other differences in ecological parameters, habitat and micro-habitat selection, and in foraging. The communities evaluated to not exhibit a structural organization based upon segregation due to competition for resources. Historical and evolutionary factors may have contributed in a signficant manner toward the structural organization of these communities.
