Geographical variation in the timing of breeding and moult in dunlin Calidris alpina on the Palearctic tundra

Studies of how organisms are adapted to regional climatic conditions are va luable when predicting the effects of global climatic changes on biota. Her e we report on the geographical variation in timing of breeding and moult o f an Arctic breeding wader, the dunlin (Calidris alpina). The Palearctic st udy sites range latitudinally between 68 and 76 degreesN and longitudinally between 46 and 179 degreesE, and encompass a variety of local climates. Th e sites were visited in sequence from west to east within 1 year, and there fore the data are not affected by confounding interannual variations. The e stimated breeding start ranged from 5 to 25 June across populations. Birds at more southern sites were found to breed earlier than those at more north ern breeding sites. Within populations, the breeding start for first clutch es spanned a period of 8 days and, when including replacement clutches, 3-4 weeks. No dunlin west of the Taimyr Peninsula were found moulting while in cubating at the nest, whereas all dunlin on Taimyr Peninsula and eastwards were in active wing moult while incubating or rearing chicks. The onset of moult in these populations ranged from 23 to 27 June. The consequences of g eographical variation of breeding conditions for variation in the annual cy cle of this species are discussed.