I propose an operational method to estimate the functional integrity of communities and assemblages of birds from their species composition. `Functional integrity' was defined as the average niche divergence (dissimilarity) of community member species. Based on a recent characterization of a consistent relationship between niche divergence (as expressed by habitat preferences and functional dependencies), and genetic divergence among bird species, an estimate of community integrity was obtained by measuring genetic distances among member species. The proposed indicator of avian community integrity (ACI) is objective in that it is based on non-selective observations of the community member species, and because the marginal effect of particular species is not fixed but depends on the other species observed. This indicator is shown to be more sensitive than species richness (SR) to disturbances such as forestry and agriculture.