Migrating shorebirds as integrative sentinels of global environmental change

Many shorebirds travel over large sections of the globe during the course of their annual cycle and use habitats in many different biomes and climate zones. Increasing knowledge of the factors driving variations in shorebird numbers, phenotype and behaviour may allow shorebirds to serve as 'integrative sentinels' of global environmental change. On the basis of numbers, timing of migration, plumage status and body mass, shorebirds could indicate whether ecological and climate systems are generally intact and stable at hemispheric scales, or whether parts of these systems might be changing. To develop this concept, we briefly review the worldwide shorebird migration systems before examining how local weather and global climatic features affect several performance measures of long-distance migrants. What do variations in numbers, phenotype and behaviour tell us about the dependence of shorebirds on weather and climate? How does data on migrating shorebirds integrate global environmental information? Documenting the dependencies between the population processes of shorebirds and global environmental features may be an important step towards assessing the likely effects of projected climate change. In the meantime we can develop the use of aspects of shorebird life histories on large spatial and temporal scales to assay global environmental change.