Trace elements (TEs), which include metals, are naturally present in the environment but their availability has been increased by human activities. Some of them play an essential role in biological functions, but all can have sublethal and lethal effects depending on concentrations. In birds, some TEs impact life history traits. All phases of the life cycle may be exposed, but the embryonic and juvenile stages are the most sensitive. During egg formation, the female transfers elements essential for embryo growth, but also contaminants that can interfere with embryogenesis. Thus, eggs are used as a biomonitoring matrix to report contamination concentrations. However, certain biological parameters can influence contaminant concentrations in eggs, e.g., laying order, number of eggs and days since the onset of incubation. Several migratory waterbird populations are declining worldwide, including the Common Eider (Somateria mollissina) population in the Baltic/Wadden Sea flyway which has declined drastically since the 1990s. Among the suggested causes, the contribution of environmental contamination remains to be clarified. The objective of this study is to evaluate the maternal transfer of TEs from females to their eggs and its variability. We sampled blood from 9 female eiders in the Bengtskär colony (Finland) during the first days of laying and then again 6 days later. At the second sampling, we also collected their eggs. Both the red blood cells and eggs were analyzed for 10 TEs (As, Ca, Cd, Cu, Hg, Mg, Ni, Pb, Se and Zn) with the ICP-MS at the department of Chemistry, NTNU. The data are still being analyzed and the results will be presented at the conference. As the Baltic Sea is one of the most contaminated seas due to its landlocked nature and land-based inputs, we hypothesize that due to the geographical position of the Bengtskär colony, the concentrations of toxic TEs are higher than previously described. We also predict that the body condition of the female as well as the order of laying are determining factors in the transfer of TEs from the female to the egg.