Studies of how organisms are adapted to regional climatic conditions are valuable when predicting theeffects of global climatic changes on biota. Here we report on the geographical variation in timing ofbreeding and moult of an Arctic breeding wader, the dunlin (Calidris alpina). The Palearctic study sites range latitudinally between 68 and 76 degreesN and longitudinally between 46 and 179 degreesE, and encompass a variety of local climates. The sites were visited in sequence from west to east within 1 year, and therefore the data are not affected by confounding interannual variations. The estimatedbreeding start ranged from 5 to 25 June across populations. Birds at more southern sites were found to breed earlier than those at more northern breeding sites. Within populations, the breeding start for first clutches spanned a period of 8 days and, when including replacement clutches, 3-4 weeks. No dunlinwest of the Taimyr Peninsula were found moulting while incubating at the nest, whereas all dunlin onTaimyr Peninsula and eastwards were in active wing moult while incubating or rearing chicks. Theonset of moult in these populations ranged from 23 to 27 June. The consequences of geographicalvariation of breeding conditions for variation in the annual cycle of this species are discussed.