THE RELATIONSHIP BETWEEN BREEDING BIRD DENSITY AND VEGETATION VOLUME

ABSTRACr.-An index of total vegetation volume was strongly correlated with breeding bird density at 31 sites in four separate studies conducted in southwestern shrub and desert habitats between 1974 and 1987. Vegetation volume was not as strongly correlated with winter bird density in two of these studies. We suggest that these correlations indicate that breeding birds respond strongly to resources associated with vegetation and that such a resource-based response may explain such well-known patterns as the edge effect and the high avian breeding densities in southwest riparian habitats. The technique we describe for measuring total vegetation volume provides a quick and accurate method of estimating this simple aspect of vegetation structure and may be useful in describing plant communities quantitatively. Received 26 Feb. 1990, accepted 29 May 1991. An underlying assumption of theoretical models of avian community