Annual variation in waterbird clutch initiation date in relation to spring thaw in Arctic Russia.

To test for the degree of species-specific variation in clutch initiation date in relation to spring thaw, we recorded first egg dates in 1433 nests of seven large bodied long-distance migratory waterbird species breeding on Ayopechan Island in the Chaun Delta, Chukotka, in the Russian Arctic during 2002-2020. Pacific Loon Gavia pacifica, Sandhill Crane Grus canadensis and Glaucous Gull Larus hyperboreus all adjusted timing of clutch initiation completely to annual variation in first frost-free dates. First egg dates of Spectacled Eider Somateria fischeri also significantly advanced in warmer springs, but the rate of change was significantly less than unity, implying a reduced capacity to accommodate change in vernal thaw that may not be able to keep up with greater change in the future.