• Fratercula arctica;
  • North Atlantic Oscillation;
  • Timing of breeding


Timing of breeding is a key factor determining the reproductive success in bird populations and known to be affected by climate fluctuations. We investigated the long-term (1978–2002) relationship between climate and hatching date within a population of Atlantic puffin Fratercula arctica at Røst in the Norwegian Sea. The timing of puffin breeding was found to be influenced by the North Atlantic Oscillation winter index (NAO). We isolated two temporal regimes, one where NAO had a significant effect on hatching date (1978–1986 and 1995–2002) and one where these variables were independent (1987–1994). Hatching date could be modelled using, in addition to NAO, hatching date and food abundance in the preceding breeding season (possibly proxies of parental effort). The models remained significant for regime 1 but not for regime 2. NAO differed between the two regimes suggesting that the shifts were induced by climate change, possibly via its effect on the availability of prey in the preceding year. The novelty of our study is the identification of temporal regimes in the effects of climate within one population.