Sea-level rise causes shorebird population collapse before habitats drown

Sea-level rise will lead to widespread habitat loss if warming exceeds 2 °C, threatening coastal wildlife globally. Reductions in coastal habitat quality are also expected but their impact and timing are unclear. Here we combine four decades of field data with models of sea-level rise, coastal geomorphology, adaptive behaviour and population dynamics to show that habitat quality is already declining for shorebirds due to increased nest flooding. Consequently, shorebird population collapses are projected well before their habitat drowns in this UNESCO World Heritage Area. The existing focus on habitat loss thus severely underestimates biodiversity impacts of sea-level rise. Shorebirds will also suffer much sooner than previously thought, despite adapting by moving to higher grounds and even if global warming is kept below 2 °C. Such unavoidable and imminent biodiversity impacts imply that mitigation is now urgently needed to boost the resilience of marshes or provide flood-safe habitat elsewhere.