Citizen science and collaborative programs help reveal coastal waterbird trends and understand the mechanisms underlying those…

Waterbirds are often used as indicators of ecosystem function across broad spatial and temporal scales. Resolving which species are declining and the ecological characteristics they have in common can offer insights into ecosystem changes and their underlying mechanisms. Using 20 years of citizen science data collected by the British Columbia Coastal Waterbird Survey, we examined trends in abundance of coastal waterbird species, both in the Salish Sea and along the outer Pacific Ocean coast, representing the core wintering coastal bird community of British Columbia, Canada. Results suggest that most populations are stable in both the Salish Sea and Pacific coast regions. However, a quarter of the species displayed significant decline trends in the Salish Sea, compared with only 8% along the Pacific coast. Guild-specific trends indicated that waterbirds occupying the Salish Sea are faring significantly worse than those residing along the outer coastal regions, almost irrespective of dietary specialization or migration distance. Our results provide evidence that differential environmental pressures between the inner and outer coastal regions may be causing overall loss of wintering waterbirds within, or abundance shifts away from, the Salish Sea. We outline potential mechanisms responsible for these observed patterns, including environmental (e.g., climate) and human-induced (e.g., nutrient and chemical pollution) pressures. We also present ongoing collaborative efforts in bird monitoring (e.g., with Indigenous communities) and research priorities to help understand these mechanisms.