Common Swifts are extreme long-distance migrants and overwinter in equatorial Africa to eastern South Africa. A precisely defined destination area is not known. The presumably continuously flying Common Swifts seem to roam over a large area depending on weather conditions (GLUTZ and BAUER, 1980). The stay in the breeding area and in the winter quarters usually covers three to three and a half months each. Breeding sites in Central Europe are normally abandoned when the young fledge, usually in the second half of July or early August. The final departure can extend until the end of August; even after that, individual passage migrants still occur (probably from more northern breeding areas), latest observations in Central Europe date around November 20. The predominant departure direction is southwest-south.
In poor weather conditions, migrating Common Swifts like to follow river courses, where they are more likely to find food than in the surrounding area. Higher mountains are probably mainly overflown in spring and late summer in good weather. The populations from Central and Western Europe migrate mainly via Spain and Northwest Africa, while Common Swifts from Southeast Europe and Russia pass through the eastern Mediterranean region. The location of the migration divide or mixing area is still unclear (GLUTZ and BAUER, 1980). On the way south, the birds follow the northwestern African Atlantic coast in large numbers, but also fly straight across the Sahara and from the moist savannas east-southeastward to the wintering area of Central Africa.
The return migration takes place on the same route, but return migration observations from both Nigeria and the Atlantic coast are relatively sparse. Common Swifts migrate singly, in flocks or even in huge groups (GLUTZ and BAUER, 1980).
Cyclonic weather flights are considered a special form of Common Swift migration. The birds avoid bad weather fronts through evasive flights that can span thousands of kilometers and last days to weeks. LACK (1956) describes that Common Swifts, unless they seek their cavities, escape approaching thunderstorms by flying ahead of the storm, later flying against the wind through the rain area and thus being exposed to precipitation for as short a time as possible. They form flocks that can reach enormous numbers of several tens of thousands of birds. This weather escape has long been known from all parts of Europe. Not infrequently, breeding birds also participate in this, whose young can survive a multi-day absence of the parents through torpidity.