1. Mute Swan (Cygnus olor):
- Global population estimated to be around 600,000 individuals.
- Widely distributed in Europe, Asia, and parts of North Africa.
2. Tundra Swan (Cygnus columbianus):
- Global population estimated to be around 150,000 individuals.
- Found in North America and Eurasia, primarily in Arctic regions.
3. Bewick's Swan (Cygnus columbianus bewickii):
- Global population estimated to be around 25,000 individuals.
- Primarily found in western Russia and eastern Europe, migrating to western Europe and the Caspian Sea region during winter.
4. Whooper Swan (Cygnus cygnus):
- Global population estimated to be around 20,000 individuals.
- Found in Eurasia, breeding in northern regions and wintering in southern Europe, the Mediterranean, and parts of Asia.
5. Black Swan (Cygnus atratus):
- Native to Australia, estimated population size is around 500,000 individuals.
- Introduced in various other parts of the world, populations vary based on the introduced locations.
It's important to note that these population estimates can vary due to factors such as environmental changes, hunting, habitat loss, and natural fluctuations. Additionally, there are other swan species with smaller population sizes, such as the Trumpeter Swan (Cygnus buccinator) in North America and the Coscoroba Swan (Coscoroba coscoroba) in South America.