Bird communities and habitat as ecological indicators of forest condition in regional monitoring

Ecological indicators for long-term monitoring programs are needed to detec t and assess changing environmental conditions. We developed and tested com munity-level environmental indicators for monitoring forest bird population s and associated habitat. We surveyed 197 sampling plots in loblolly-shortl eaf pine forests, spanning an area from Georgia to Virginia (U.S.A.) and re presenting a gradient in levels of anthropogenic disturbance. Ninety of the se plots were randomly selected from a sampling grid, permitting quantitati ve assessment of cumulative distribution functions for bird community and h abitat parameters. Species were independently classified into habitat assem blages indicating birds typical of disturbed habitat (e.g., shrubland, fore st edge) and undisturbed habitat (mature forest). Relative abundances of th ese assemblages were used to form a bird community index-similar to the ind ex of biotic integrity applied to aquatic systems-showing the effects of ha bitat disturbance on forest bird communities. Bird communities on the major ity of the sample area (52-75%, 90% confidence interval) were dominated by disturbance-tolerant species. Sites dominated by mature-forest species were comparatively uncommon. Habitat assemblages appeared to be particularly us eful tools for environmental monitoring; individual species abundance was p ositively correlated with assemblage species richness, and assemblage membe rs showed consistent responses to variations in disturbance level. To a les ser extent, component species of nesting guilds showed this pattern of cohe sive responses, but those of foraging guilds did not. We also developed a h abitat index based on habitat variables that predicted bird community index values. Habitat and bird community indices were strongly correlated in an independent validation dataset, suggesting that the habitat index can provi de a reliable predictor of bird community status. The two indices may be us ed in combination, with the bird community index providing a direct measure of the status of the bird community and the habitat index providing a basi s on which to separate changes in the bird community into local habitat eff ects versus other factors (e.g., landscape level effects, changes on winter ing grounds).