Bird migration occurs in the airspace of Mongolia during the whole year, but culminates in the periods Mid-February to beginning of June (spring migration) and Mid-August to end of November (autumn migration).
The most important factor inducing heavy migration is change in temperature.
Major bird flyways in the Asia-Pacific region include West Pacific Flyway, East Asian-Australian Flyway and Central Asian-Indian Flyway.
West Pacific Flyway migration crosses Eastern Mongolia, East Asian-Australian Flyway migration crosses entire territory of Mongolia and Central Asian-Indian migration crosses Western Mongolia respectively.
The main bird migration routes in Mongolia are:
- Khalkh River-Kherlen-Dalai Lake;
- Nomgon-Ulaan Lake-Orkhon-Selenge;
- Boon Tsagaan Lake-Orog Lake-Baidrag /Tuin River/- River Valleys of Khangai Mountains, Khuvsgul Lake;
- Khalkh River-Kherlen Tuul-Selenge;
- Ulaan Lake-Boon tsagaan-Khar Us Lake.
During summer, most birds fly at altitudes no less than 500 M. However, predatory birds fly at altitude of 1500 M-2000 M, with eagles and vultures at up to 6000 M in some cases. Generally the altitude of night migration is higher than by day.