| Summary: | The colony of Atlantic puffins (Fratercula arctica) at Hjelmsøya, in Northern Norway has experienced extensive annual fluctuations in breeding success. To investigate how climate variability affects the population dynamics of this iconic seabird, I have analysed data on breeding success for this colony for the past 10 years. Through analysis of the time-series data I wished to investigate which climate and oceanographic conditions that best explained the variance in breeding success. My hypotheses were that 1) the short-time variation apparent in breeding success is best explained by climatic conditions in the months leading up to the breeding season, and that 2) this effect will be most apparent indirectly, through the availability of prey. Where earlier studies mainly consider the NAO index as a parameter for climate variability, I have included several other teleconnections to account for other modes of climate variability in the Northern Atlantic. The abundance of cod larvae in the Barents Sea was the single variable that explained most of the variance in breeding success, having a significant positive effect on breeding. I found that the effect of climate on breeding success for the puffin colony at Hjelsmøya was most apparent indirectly, through the availability of cod larvae in the Barents Sea, which had a significant positive effect on breeding success. While commonly used climate teleconnection patterns, such as NAO, could only weakly explain the variance in breeding success, the effect of NAO on abundance of cod larvae was considerably stronger. This supports the hypothesis that the effect of climate is most apparent indirectly, through the availability of prey. In addition, the multiple regression model explaining most of the variance was the model including NAO, cod larvae abundance and cod larval drift as covariates. Thus, the causal pathway by which climate seems to influence breeding success is by its effects on oceanic currents affecting larval drift and thereby the amount of fish larvae ...
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