Breeding bird populations were studied in mesquite and cottonwood habitats on the lower Verde River in south-central Arizona [USA]. The cottonwood plot had a high avian density, the highest number of species and the highest bird species diversity (BSD) in comparison to other Verde River cottonwood habitats. This was probably due to high tree understory density and high foliage volume (FV) of shrubs which contributed to a high foliage height diversity (FHD) and total foliage volume. The mesquite site had a high avian density, a high BSD and a high number of avian species in comparison to other mesquite habitats. Although few comparable vegetative measurements were available, some major differences among these mesquite habitats such as higher average tree height and presence of permanent water near the plot of the present study might account for higher avian numbers. The relationship between BSD and FHD remains ambiguous, although BSD of cottonwood and mesquite habitats of the Southwest appear correlated with FHD. For cottonwood habitats in Arizona, BSD was correlated with percent vegetative cover (PVC), a measure of foliage volume. BSD was weakly correlated with foliage volume, determined by the point-quarter method for riparian woodland habitats on the Verde River in Arizona. FHD, PVC and FV appear indefinite predictors of BSD. Therefore, breeding birds should be censused on study plots for consecutive years due to fluctuations in species diversities from year to year with seasonal measurements of habitat structure, fruit crops, and other resources to determine the relationship between vegetative structure and avian populations.