Epsilon Archive for Student Projects

Abstract

Seabirds, including the Common Guillemot Uria aalge, are important bioindicators of marine ecosystems. Understanding their dietary habits provides critical insights into habitat status and changes in food availability. The aim of this study was to gain a deeper insight into the adult Common Guillemot diet in the Baltic Sea and investigate whether it differs from previously investigated diet of chicks. In this study, 50 adult faecal samples were collected at Stora Karlsö, the largest Common Guillemot colony in the Baltic Sea, prior to chick hatching in June 2024. DNA concentrations from three key prey species – sprat Sprattus sprattus, herring Clupea harengus and three-spined stickleback Gasterosteus aculeatus – were quantified using digital PCR (dPCR), a type of environmental DNA (eDNA) method. The results showed that the adult diet consists of a more diverse composition and other proportions than illustrated in previous adult diet research. This may be due to seasonal or time effects with differences in prey abundance. Furthermore, the result revealed a more diverse adult diet (45% sprat, 27% herring, 27% stickleback) compared to the chick diet (71% sprat, 23% herring, 6% stickleback), with a statistically significant difference confirmed by a Chi-square test of independence (p < 0.00001). These findings indicate that the adult birds self-feeding differs from their chick provisioning, likely reflecting differences in their nutritional requirements and foraging strategies. Since the Common Guillemot is a single-prey loader, it is probably more efficient for the adult to bring a large fish of high calorific value back to their chick. While the parents for self-feeding can make do with smaller, low-quality fish. The study emphasizes the value of eDNA analysis in faecal samples for seabird dietary research. It also highlights the need for further studies to deepen our understanding of the dietary differences between adult and chick Common Guillemots in the Baltic Sea. For instance, it would be interesting to monitor the same individuals over time to examine whether the adults consistently target the same prey when self-feeding, or if their diet varies from day to day.