It is just after noon in Mexico’s Monarch Butterfly Biosphere Reserve, and the sunrays filtering through oyamel fir trees have caused an awakening. Cascading from their dense clusters around the tree trunks, the delicate orange and black monarchs flutter through the forest, alighting on woodland flowers and holding still for an instant before resuming their dance. By mid-March, they will be gone, beginning their migration north, where they lay their eggs on milkweed that grows wild across the Great Plains of the United States and Canada. Four generations later, the butterflies will return next November—after flying as far as 4,500 km (2,800 miles)—to spend the winter here in the cool pine, fir and oak forests of these volcanic mountains. But as they prepare to leave, many experts fear that few of the monarchs will return. Their numbers have declined steadily, and this past winter marked the smallest... [Log in to read more]