Monarch Butterfly Migration

A multigenerational migration in which North American monarch butterflies travel up to 4,800 kilometers between their northern breeding range in the United States and Canada and their overwintering sites in the oyamel fir forests of central Mexico, with much of the journey completed by several successive generations that have never made the trip before. The migration relies on an inherited, poorly understood sense of direction rather than learned experience, and its overwintering colonies, which can cover trees so densely the branches bend under their weight, have become one of the most celebrated wildlife spectacles in North America even as the population has declined sharply in recent decades.