| Studies of the bird community were conducted during avian breeding seasons from 1988 to 1991. Five plots were located in pine-oak-juniper and related woodlands in the Chiricahua Mountains of southeast Arizona. Habitat characteristics such as variation in weather patterns, vegetative composition and structure, and insect density and distribution were measured. These were then related primarily through regression analysis and ANOVA's to characteristics of bird community composition and structure.;Annual and quarterly precipitation averages were found to be related to various aspects of vegetation and insect resources. Precipitation variables were also found to be related to measure of bird community composition and structure, especially long-term precipitation trends. Both primary production characteristics (vegetation), and primary consumer characteristics (insects) were strongly related to avian community characteristics. Combining productivity measures at two trophic levels improved the ability to partition the variance in bird density and diversity compared to considering only one trophic level. No clear determinant of bird species richness was found among the variables measured in this study. Overall, the community was shown to respond directly to resource variability among habitats, and among years.;Within this general pattern of resource responsiveness, competition was shown to influence certain species' habitat utilization and densities: competition was evidenced by niche shifts, density compensation, and other means. Member species of the foliage gleaning guild utilized available resources in a close association by distributing themselves across the resource spectrum in an ideal free manner. In the long-term, these associations of productivity and competition with avian community characteristics are found to be relatively stable through time, as shown by comparison of this study to similar data collected in the 1960's and 1970's (M. L. Cody 1981, Bioscience 31:107-113). |
