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Causes and consequences of timing of breeding in Common Guillemot, Uria aalge, in the Baltic Sea
Sundberg, J. (2008) Degree project thesis, Department of Systems Ecology, Stockholm University
Timing of breeding in Common guillemots at Stora Karlsö, central Baltic Sea, is determined by the size of the sprat stock and March sea surface temperature. These factors together explains 64 % of the inter-annual variation, based on data from the 1970ths and 2000ths. However, in the recent years, temperature seems less important, and I interpret this as guillemots are nowadays not physically constrained for breeding early because of the increased Baltic Sea sprat stock. Guillemots in the Baltic Sea feed almost exclusively on sprat, which has a spawning period with larger inter-annual variation in timing (several weeks) than guillemots (7-10 days). Using survival data for chicks ringed during the 2000ths, my results suggests that optimal timing of breeding for guillemots varies between years, and is probably linked to spawning timing in sprats.

Keywords: Common guillemot, Uria aalge, Sprat, Sprattus sprattus, timing, match, mismatch, sea surface temperature, Baltic Sea.


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