| Summary: | Populations living close together in space are likely to experience more similar environmental fluctuations, and thus may display similar temporal changes in population parameters, in other words synchrony. Interspecific synchrony has implications for ecosystem stability, and highly synchronous populations and communities tend to have a higher risk of extinction. In this thesis, I used long-term data from six seabird species, breeding at Hornøya colony in the Barents Sea, to analyse the degree of synchrony in breeding success. I then investigated potential environmental drivers of inter-specific synchrony, and also asynchrony, in their breeding success. A generalized linear model (GLMs) was fitted to the breeding success data of each species. Pairwise correlations of the model residuals were calculated for all species combinations. Model selection was performed including climate and oceanographic covariates, which were considered to possibly influence breeding success, to identify the best model of breeding success for each species. If a covariate was included in the best-fitting model for multiple species, I tested the extent to which that shared effect led to interspecific synchrony. A higher level of synchrony in breeding success was found between auks and between gulls, than between these groups of birds. Atlantic water-inflow during winter was identified as a driver of breeding success, with potential synchronizing effect for kittiwakes (Rissa tridactyla), great black-backed gulls (Larus marinus) and herring gulls (Larus argentatus). For Atlantic puffins (Fratercula arctica) and razorbills (Alca torda), a lagged effect of Atlantic water-inflow during winter on breeding success was found. Sea surface temperature was identified as a potentially synchronizing driver of breeding success for great black-backed gulls and herring gulls. The results indicate that climate-induced changes in the Barents Sea ecosystem can have pronounced effects on seabirds breeding on Hornøya.
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