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.