Causes and Consequences of Breeding Synchrony in the Snow Bunting (Plectrophenax nivalis )
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- Institutt for biologi 
Climate warming is happening rapidly in the Arctic and migratory birds are among the species expected to be affected by the predicted shifts in spring phenology. Using time-series data (1998 - 2014) from a population of snow bunting (Plectrophenax nivalis) nesting in High Arctic Svalbard, I investigated climatic effects on interannual variation in breeding synchrony and its fitness consequences. Breeding synchrony was here defined as the temporal synchrony in egg-laying on the population-level, which was estimated using a Synchrony Index (SI). Multi-model comparisons of linear regression models were used in three sections of analyses; i) onset of breeding in relation to climate, ii) breeding synchrony in relation to onset of breeding and climate, and iii) reproductive success in relation to breeding synchrony and climate. Timing of onset of breeding was negatively related to spring temperature. Furthermore, SI was positively related to spring precipitation and onset of breeding. Reproductive success, measured as mean number of fledglings, was positively related to breeding synchrony and mean summer temperature. This long-term study gives insight to how the breeding phenology of a passerine migrant is affected by local climatic conditions in the High Arctic. The present study indicates that the dynamics of the study population may be altered with expected climatic warming.