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travel / adventure zone
| The Adventure Zone |
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Monarchs in forest clearing.
Photo: Dr. Lincoln Brower, Sweet Briar College (brower@sbc.edu). |
Monarch Redux
The death-defying (and mind-boggling) annual migration of Danaus plexippus
By Tracy C. Read
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Monarchs
on the move.
Photo: Dr. Lincoln Brower, Sweet Briar College (brower@sbc.edu). |
Consider the monarch butterfly. A glimpse of its familiar orange-and-black wings fluttering in the distance is a welcome sign of renewal each spring. Yet how many of us stop to appreciate that this delicate creature and its forebears have battled mountains and valleys, fierce winds and rain, snow, hunger, predators and thousands of wearying kilometres to make this ephemeral appearance in our gardens?
The monarch, weighing in at a feisty half a gram, is truly one of nature's migratory giants. This spring, southern Canadians living east of the Rocky Mountains will welcome back the first- and second-generation offspring of the intrepid monarchs last seen in August, just before their arduous journey to their overwintering grounds. After sweeping down the continent in cone-shaped formations, monarchs by the millions reach their southern destination in November. Then, atop 12 mountaintops in central Mexico, their winter sojourn begins.
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Rust-coloured patches show monarchs clinging to Oyamel firs in central Mexico.
Photo: Dr. Lincoln Brower, Sweet Briar College (brower@sbc.edu). |
It is not an easy life. At a cool 3,000 metres above sea level, the monarchs make their temporary home among Mexico's dwindling Oyamel fir forests. Sheltered from rain and snow by the forest canopy, they cling to the branches, kept in a semi-dormant and non-reproductive state by the high altitude and low temperatures and moving as little as possible in order to preserve energy for the spring journey home.
Just around the vernal equinox in the third week of March, as the days grow longer and their reproductive systems kick in once more, the surviving monarchs head north, searching for sprouting milkweed. After mating and laying their eggs on the milkweed plants, the breeding generation, battered and bruised, expires. The larvae feed on the milkweed leaves (the only food they will touch), then enter the pupa stage. Five weeks later, the rebuilt adult monarchs emerge and continue the journey north. They still have thousands of kilometres to go before they grace our gardens — a home previously known only by their parents.
The many mysteries of the monarch's migration have preoccupied scientists for decades. Today, as this butterfly's survival is increasingly threatened in both its seasonal homes — with the Oyamel fir forest habitat in the south reduced by logging and urban sprawl and herbicides eliminating critical milkweed plants in the north — that interest has only intensified. Students of all ages can join the adventure of the 2008 monarch migration at www.learner.org/jnorth/monarch/
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