Migration of birds as an indicator of broad-scale environmental condition.

The migration of Neotropical birds may provide a robust measure of changing environmental condition along the migratory route. I review previous work on assessing broad-scale stopover quality in the eastern United States and discuss how future research can aid regional environmental assessment. Scientists can quantify how environmental changes affect the migratory system, and then monitor for those effects on migrant abundance from year to year. The cyclical nature of migration provides a constant re-evaluation of habitat quality and spatial distribution by migrant birds. Avian monitoring programs can detect changes in migrant abundance. Migrating birds may thus provide a living sensor of environmental change, enabling broad-scale environmental assessments to detect and address habitat degradation early on, allowing local managers to prioritize restoration efforts accordingly. Understanding the environmental factors driving stopover selection, and how birds move between stopovers during migration, is an important first step.