The impacts of seventy years of changes in stopover habitats on the critically endangered Spoon-billed Sandpiper Calidris pygmaea

Natural habitat loss due to land use change is a major driver of global biodiversity loss. Human-created seminatural environments can function as artificial habitats for many species, partially offsetting these negative impacts. However, it remains unclear how species respond to the short- and long-term changes in both natural and artificial habitats, particularly for long-distance migratory species at stopover sites. We investigated how the globally endangered habitat specialist species, Spoon-billed Sandpipers Calidris pygmaea, responded to 70 years of changes in natural wetlands, sandy beaches, and artificial wetlands across stopover habitats in the Japanese Archipelago. We compiled historical observation records of the species from multiple sources and quantified the extent of these three habitat types from 1950 to 2020. Spoon-billed Sandpiper abundance consistently declined from the 1970s to the 2010s, with a particularly sharp decrease between the 1980s and the 1990s. While more than 50% of natural wetlands and sandy beaches have also been lost since 1950, we found that sandpiper abundance was lower at sites experiencing greater cumulative natural habitat loss. By contrast, changes in artificial wetland extent were not significantly associated with abundance, despite their temporal expansion peaking in the 1970s and subsequently declining. Our findings demonstrate that historical loss of natural stopover habitats have had lasting negative effects on local sandpiper populations, and the temporary expansion of artificial wetlands failed to compensate for these effects. This underscores the critical importance of preserving the networks of natural stopover habitats to sustain migration success, particularly for habitat specialists.