Drift is assisted by disorientating conditions such as mist or drizzle, and can result in large numbers of birds arriving together in an area in which they are not normally seen. In the UK this is called a fall, while in the U.S. it is known as a fallout, though in the latter case, it need not involve vagrant birds.
An example would be an east wind in September blowing migrants such as , , and the continental race of European robin onto the east coast of England and Scotland, leading to temporary concentrations of these species at headlands like Spurn.
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