''See also vagrancy (people) for an alternative use of the term

Vagrancy is a phenomenon in biology whereby individual animals appear well outside their normal range; individual animals which exhibit vagrancy are known as vagrants. The term accidental is sometimes also used. There are a number of factors which might cause an individual to become a vagrant — genetic factors and weather conditions are two — but the causes are overall poorly understood.

Vagrancy can be a precursor to colonisation if individuals survive.

Vagrancy is known to occur in birds, insects, mammals and turtles.

Vagrancy 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, as are North American birds which have been blown across the Atlantic Ocean by storms.

Vagrancy in insects

Vagrancy in insects is recorded from many groups — it is particularly well-studied in butterflies and moths, and dragonflies.

Vagrancy in mammals

In mammals, vagrancy has been recorded for bats, seals, and kangaroos.

Vagrancy in reptiles

Vagrancy has been recorded for turtles.

Ecology

Irrgast | Dwaalgast