Vagrancy is a phenomenon in biology whereby an individual animal (usually a bird) appears well outside its normal range; they are known as vagrants. The term accidental is sometimes also used. There are a number of poorly understood factors which might cause an animal to become a vagrant, including internal causes such as navigatory errors (endogenous vagrancy) and external causes such as severe weather (exogenous vagrancy). Vagrancy events may lead to colonisation and eventually to speciation.
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