Geographical distribution of Tundra swan.    Breeding  Migration  Nonbreeding
BirdLife International. 2016. Cygnus columbianus. The IUCN Red List of Threatened Species 2016: e.T22679862A89644875. https://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22679862A89644875.en. Downloaded on 01 July 2018.
Cephas