Bellebaum, J., Kube, J., Schulz, A., Skov, H. and Wendeln, H. 2014. Decline of Long-tailed Duck Clangula hyemalis numbers in the Pomeranian Bay revealed by two different survey methods. Ornis Fennica. 91, 3 (Sep. 2014), 129–137. DOI:https://doi.org/10.51812/of.133850.