Vagrancy (biology) - in Birds

In Birds

In the northern hemisphere, adult birds (possibly inexperienced younger adults) of many species are known to continue past their normal breeding range during their spring migration and end up in areas further north (such birds are termed spring overshoots.)

In autumn, some young birds, instead of heading to their usual wintering grounds, take "incorrect" courses and migrate through areas which are not on their normal migration path. For example Siberian passerines which normally winter in Southeast Asia are commonly found in Northwest Europe, e.g. Arctic Warblers in Britain. This is reverse migration, where the birds migrate in the opposite direction to that expected (say, flying north-west instead of south-east). The causes of this are unknown, but genetic mutation or other anomalies relating to the bird's magnetic sensibilities is suspected.

Other birds are sent off course by storms, such as North American birds, blown across the Atlantic Ocean to Europe. Birds can also be blown out to sea, become physically exhausted, land on a ship and end up being carried across the ocean.