A “demand and supply” approach to monitoring habitat and population changes of migratory birds

Habitat loss and degradation threaten thousands of migratory bird species worldwide. Yet, because the distributions of migratory birds change throughout the year, quantifying the impacts of threats and identifying key sites for conservation attention have proved challenging. We suggest that the wider application of two key metrics could substantially improve current knowledge: (1) the intensity of birds’ habitat use at a site, representing the demand from the birds’ perspectives; and (2) the carrying capacity of the site, as measured by the supply of food or other resources for the birds. At local scales, the demand-to-supply ratio provides insights into priorities for conservation attention, even in the absence of comparable information from other sites. When scaled-up to multiple sites across entire flyways, this approach provides a much more comprehensive understanding of the constraints on bird populations than is currently available, thereby facilitating coordinated, efficient habitat protection at a flyway scale.