1. Sensory and Cognitive Ecology; University of Rostock, Institute for Biosciences; Rostock 18059 Germany
2. Department of Anatomy; Rostock University Medical Center; Rostock 18057 Germany
3. University of Hamburg, Biocenter Grindel, Institute of Zoology and Zoological Museum; Hamburg 20146 Germany
4. University of Veterinary Medicine Hannover, Institute for Terrestrial and Aquatic Wildlife Research; Büsum 25761 Germany
5. Department of Arctic and Marine Biology; University of Tromsø-the Arctic University of Norway; Tromsø 9037 Norway