The Mystery of the Monarchs

  Angangueo, Mexico
Thursday, March 15, 2007

Wow!! Sheer magic!! Last week we had another of those experiences that will stand out as one of the highlights of our trip. We spent a day at El Rosario Monarch Butterfly Sanctuary high in the hills of Michoacán state about 200 km west of Mexico City. Talk about bowled over - we were totally captivated and utterly fascinated by the amazing mystery of these colourful, seemingly fragile, little winged creatures. Of course, we've all heard the story of their incredible migration back and forth from the Great Lakes area of the US and Canada to the Mexican highlands, but to actually stand there and be surrounded by this fluttering mass of millions of brilliant orange, yellow, black and white butterflies as they gather strength for their long journey north is really something to behold. Although many hypotheses have been formulated and theories proposed by entomologists and environmental scientists, it seems that the "why" and the "how" of their great annual trek still remains a mystery. Another delightful and tantalizing puzzle of the natural world that will hopefully elude a rational explanation for some time yet!

We camped overnight in the parking lot of the Sanctuary and early in the morning ran the gauntlet of the enterprising vendors with their tacky souvenir stands and grubby food stalls as we started the hike up into the pine and fir forests. It was a beautifully bright, sunny day and already there were a few of the distinctive monarchs fluttering around soaking up the warmth. Cameras at the ready, we were determined not to miss any shots in case we might already be too late, as the migration usually starts around the middle of March. Not to worry, we ended up with literally hundreds of photos, and for the first time in three years filled the one gigabyte memory card on the camera within a few hours! By mid-morning the flowering bushes and shrubs beside the path were a swarming mass of butterflies busily seeking mates and following the complicated rituals of the mating game.

Maybe some background on the biology is in order (you're allowed to skip this paragraph if you're not interested in the technical details!). Apparently the increasing temperatures and day-length in February and early March trigger the sexual development of the monarchs (Danaus plexippus), and once mature they mate on the wing, with the male carrying the female around until they finally fall to the ground and struggle to disengage. This effort is too much for the males and within days they will all be dead, littering the ground, their task accomplished. The females are the ones who journey north, and will cover the incredible distance of several thousand km in a few weeks by taking advantage of the high altitude northerly airstream, gliding most of the way. In the southern US states around the Gulf of Mexico they will literally come back down to earth in late April in order to lay their eggs on milkweed plants and other members of the Asclepias genera. After about a month the larva and pupa cycle is complete and the next generation of adults then continues the migration, arriving in the Great Lakes area for the summer months. Two or three more generations are produced there with a life cycle of about a month each, and are totally dependent on milkweed for their sustenance. They are clearly able to tolerate the toxic qualities of the latex of the plant, and in fact the brightly striped larvae utilize it as a defence to deter potential predators. The final reproductive cycle results in adults - called the 'Methuselah Generation' - who are physiologically quite distinct and have a life cycle of about eight months. These are the adults - about a 100 million of them - who return to Mexico in the fall for the winter hibernation, with the females completing the migration cycle to the southern US the following spring.

Enough of the boring entomology, back to our hike! We had soon reached an altitude of almost 9,000 ft up amongst the fir trees - locally known as 'Oyenal' - which provide the butterflies with their protective overwintering habitat, and the branches were still laden down as if with colourful fall foliage. In a nearby meadow a damp patch of earth attracted so many that the ground seemed to be a vividly coloured, living carpet, occasionally bursting into a flurry of aerial activity. We sat and watched, totally entranced, and when we moved on we had to be extremely careful in order to avoid extinguishing a dozen lives with a misplaced footstep. There were butterflies everywhere - the air was full, the ground was covered, the trees were brimming, and it seemed that even the sky was darkened with their multitudes. Within days all the females would be winging their way northwards, leaving the ground littered with their dead male consorts. Later in the afternoon we reluctantly dragged ourselves away, and headed back down the hill marvelling at this wonder of our world.

Most of what is known today about the monarch migration is due principally to the pioneering work of Canadian researcher Dr. Fred Urquhart at the University of Toronto and continued today by Dr. Orley 'Chip' Taylor at the University of Kansas. Thousands of volunteers have been involved in a massive tagging program which monitors the movements of individual butterflies, and research continues under programs such as Monarch Watch (www.monarchwatch.org). Universities, state and provincial governments in Mexico, the US and Canada are all involved, as are numerous international environmental organizations and foundations. It took intensive work by Dr. Urquhart from 1935 until a breakthrough in 1973 to even discover the exact location of the monarch's winter home, and it appears that there is still potential for lots of research yet.

We learned later that five sanctuaries have been established by Mexican presidential decree in this area since the mid-80s, totalling over 16,000 ha, in order to preserve the winter habitat. A lot of work has been carried out with the local communities to explain why these forests have to be protected, and certain activities curtailed during the November to March hibernation period. However, even today some landowners are not in agreement with the restrictions and occasionally start forest fires in protest. However, in the north the monarch's summer habitat is under a more insidious threat. Clearing of land, urbanization and the increasing use of herbicides in Canada and the US poses a real problem with regard to eradication of the milkweed plant, which is essential to the monarch's survival. Now, this is where you come in. Are you in the habit of pulling the milkweed out of your garden in the summer because you think it's just another noxious weed? Well, hopefully by the time you've finished reading this you'll have changed your mind and will consider giving these incredibly beautiful and complex butterflies sanctuary in your backyard each summer. You won't regret it!