By Allan Britnell

With its distinctive black, orange and white-speckled patterning, the monarch (Danaus plexippus) is probably the best known of all North American butterflies. It is also one of the continent’s most well travelled insects, migrating more than 3,000 kilometres from its summer retreats as far east as Newfoundland to its overwintering grounds in Mexico.

Despite those overwintering grounds being designated as protected reserves, however, the butterfly’s habitat is under threat from logging and clearcutting for farming and so is closely monitored. Destroying monarch habitat in Mexico is especially devastating to this species, because the entire North American population of monarchs east of the Rockies overwinters in one of about a dozen high-altitude Oyamel fir forests, all found within an 800-square-kilometre area.

In late 2009, observers in Mexico estimated that the entire population was overwintering in a combined area of less than two hectares, the smallest winter range ever recorded. Then, in February 2010, an apocalyptic combination of heavy rains, hail and freezing temperatures devastated the region, wiping out at least half the monarch population. “Many of us were uncertain about what recovery the monarch population would make in 2010,” says long-time Ontario Nature member Don Davis, who has been tagging monarch butterflies since 1968 and is a co-author of the North American Monarch Conservation Plan.

Luckily, heavy rains in Texas had an opposite effect, ending a long-term drought and ensuring an abundance of milkweed, the primary food source for monarchs. By the time these butterflies reached Ontario in May, favourable conditions had already resulted in an early appearance of milkweed. Monarch tallies throughout the summer showed promising numbers.

This fall’s migration statistics were even better. In early September, an estimated 10,000 monarchs were spotted roosting at Presqu’ile Provincial Park, the largest concentration seen there in decades. The same day, observers counted 100 to 130 monarchs passing by the cliffs at Port Stanley every minute.

Davis is optimistic. “We hope that this successful migration will mean an increase for the overwintering population in Mexico.”