Monarch Butterfly Migration

Between January and March each year, an estimated 60 million monarch butterflies overwinter in the Monarch Butterfly Biosphere Reserve, making it one of the biggest congregations of a single species anywhere in the world.

The entire population squeezes into less than 3 hectares. They cluster on the trees in numbers so dense, the blaze of their wings turns the dark green foliage of the forest fir orange.

The migration starts in September and October when they journey south from across the USA and southern Canada, to escape the North American winter.

The migration north to south, and then back again in spring, is continuous. No single butterfly completes the full circuit in their short lifetime – it’s estimated four generations are required.