Journal Article
Nuijten, R.; Kölzsch, A.; van Gils, J. A.; Hoye, B. J.; Oosterbeek, K.; de Vries, P. P.; Klaassen, M. L.; Nolet, B. A.: The exception to the rule: Retreating ice front makes Bewick’s swans Cygnus columbianus bewickii migraiton slower in spring than in autumn. Journal of Avian Biology
45 (2), pp. 113 - 122 (2014)