| Summary: | Abstract Migratory birds breeding at high latitudes face challenges in relation to timing of breeding vs. annual weather, climate change, and predator abundance. Hunting pressure along migration routes and wintering quarters forms an additional challenge. We studied population structure and interaction with environmental factors in a small population of threatened Lesser White-fronted Geese Anser erythropus, living in sub-arctic zone in Lapland in 1989–1996. Thereafter the population disappeared. The population comprised 2–15 breeding pairs plus 0–12 non-breeders, which left in June to moult elsewhere. 30 broods were observed (0–8 annually) with an average number of 2.9 goslings. Of the 3 satellite tagged plus 7 ringed geese at least 3 were shot and altogether 4 killed during the first year. Only 2 were seen alive next year or later. Laying started on average 4 June (21 May–13 June) and hatching took place 2 July (21 June–10 July) with an intra-seasonal clutch size decline. Variation in nesting initiation was not explained by local phenology, but instead by the date of staging peak in the last pre-breeding staging area 600 km south. Reproduction was affected negatively by cold spells and positively by the sum of daily effective temperatures by 5 July. Vole populations were low and a real cycle missing. No effect of reindeer abundance or human presence on reproduction could be found.
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