Seasonal variation in fledging age among common guillemot (Uria aalge)

Sammanfattning

The common guillemot (Uria aalge) is a good indicator species. The breeding success and development of the chicks can truly tell us a lot about change in the habitat and surroundings. A seasonal decline in fledging weight among the common guillemot chicks on Stora Karlsö has been discovered. The difference in fledging age has been proposed as one of the possible reasons for the seasonal decline of the fledging weight. Other explanations proposed are a seasonal decline in food quality or food quantity. The aim of this study is to get a better understanding of the seasonal decline in the fledging weights of the common guillemot chicks on Stora Karlsö. By examine if the observed weight decline late in the season is attributed to younger fledging age among late fledged chicks. In this study secondary data from an existing database from AukLab on Stora Karlsö was used to analyse the fledging age among 270 chicks between 2022 and 2025. In conclusion, the results of the analysis indicated that the fledging age increased later in season. Another conclusion was that the age of the chicks fledging four or more days after the average fledging date had a higher variance.