every autumn, tens of millions of monarch butterflies travel to their ancestral winter roosts in mexico’s mountain fir forests, coating the trunks of the trees in the orange of their wings, and causing the branches to droop under their collective weight.
surfing winds from southern canada and the northern united states, and taking directional cues from the sun and magnetic poles, they travel 4,500 kilometres over two months to reach their hibernation grounds — a feat that still remains a bit of a mystery, but which has been going on for millions of years.
interestingly, the autumn migration south is accomplished in one generation, which lives for about seven months, while the spring migration north is done over three generations, each living about six weeks.
last year’s migration, however, was the lowest on record, as excessive herbicide usage has reduced the supply of the milkweed plant which the monarch larvae rely on to feed, and which makes the monarch caterpillars toxic to predators. but the plant is now being destroyed from heavy use of roundup ready pesticides used in soy and corn crop production.
further complicating matters for the monarch is climate change, as drought along their migratory route has exacerbated milkweed decline, and colder spring temperatures has meant the temperature-sensitive cold-blooded butterflies are unable to begin their journey north.
and once they reach their hibernation sites in mexico, the butterflies, which rely on a thick forest canopy for protection from the cold and rain, encounter deteriorating forests from illegal logging.
experts, however, are hopeful that this year’s migration will double or triple, thanks in large part to the conservation efforts of the mexican government. nevertheless, this increase would still put monarch numbers at one tenth of their record high of one billion.
photos by (click pic) joel sartore, paul bettings, lincoln brower, thomas d mengelsen, and ingo arndt