by Karin Leperi Pezo / text and photos

It happens every year.  Some scientists say it has happened for the last 40,000 years.  Millions of monarch butterflies migrate from Canada to México, seeking the same high altitude, southern forests, and the same trees in which to overwinter.  After spending the summer in Ontario, Canada, the monarchs will instinctually congregate at the tip of Point Pelee, around mid-summer to early fall.  There, they patiently await favorable winds to assist their winged crossing of Lake Erie, starting the annual migration cycle that puzzles scientists even as it fascinates travelers from around the world.  

Without a road map or GPS to plot their arduous journey, the monarch precisely navigates thousands of miles, covering three nations as they migrate to their winter grounds in the mountains of Michoacan, México. This is the path for the majority of monarchs east of the Rockies.

During this record-breaking flight from Canada, across the United States, and into the heartland of México, some 250 million monarchs will fly to federally protected forest lands to hibernate and then mate in the spring.  They travel only by day, ultimately covering a distance between 2,500 – 3,000 miles, fluttering as high as 10,000 feet. A true “super commuter,” no other butterfly even comes close. 

Though the journey is repeated every year like clock-work, scientists are still not certain how the monarchs find their way. Some scientists think that the Monarchs instinctually use the Earth’s magnetic field and the position of the sun.  Whatever the source, they arrive usually just after Halloween and the Mexican day of the Dead holidays.  In a collective frenzy designed to protect the insects from temperature extremes and dryness, the monarchs drape themselves from oyamel fir trees by the millions, hanging together like gossamer blankets of orange and black webbing, loosely woven, but interconnected.  

It’s easy to see why this stunning spectacle attracts both scientists and tourists.  Though there are five protected sites for the winged wonders of winter, some sanctuaries are open only to scientists.  However, two of the largest are available to the public:  El Rosario and Sierra Chincua.  About four hours from México City, Angangueo is the usual starting point for sanctuary tours of “Las mariposas.” 

After spending a winter huddled in trees at 10,000 feet, the warming winds of March beckon the monarchs to begin their northward journey to Canada, where they will search for milkweed plants to lay their eggs. Milkweed is the only plant that the caterpillars eat. Abundant and adaptable, the plant thrives throughout the United States and north of the border into Canada.  As the plants contain poisons that don’t affect the larvae but do affect birds who try to eat them, the result is that most birds learn to avoid the larvae and adult stage of the monarch. The poisons, known as cardiac glycosides, serve as a protective defense from predatory birds.

In early June, the butterflies reach Ontario; however, they are not the same butterflies that over-wintered in México.  Most that leave México will make it as far as Texas before instinctual breeding occurs.  Here they will mate, lay eggs, and perish.  It is only after three or four generations of breeding, dying, and new generations continuing the flight north, that the monarchs eventually reach Canada and an abundant source of milkweed.  

Meanwhile, the west-coast “kissing cousin” of the eastern monarch has a journey almost as long.  While many may traverse three nations, most will confine their migration to two nations instead, opting to terminate their flight from Canada to somewhere along the coastline of California. 

They don’t travel as far and they show an adaptive preference for eucalyptus and Monterey pines.  And though millions of east-coast monarchs migrate to the Transvolcanic Belt in central México, the west-coast variety has numbers in the thousands instead, descending on about 300 sites from south of Ensenada, Baja California, to north of San Francisco, in Sonoma County.  

Though the monarch migration remains a mystery, one thing is for certain.  Next year, the monarch cycle will repeat itself once again, just as it has for the last 40,000 years.

For more information:

www.MonarchWatch.org

Monarch Watch is a program managed by the Department of Entomology, University of Kansas, Lawrence, KS  66045.

SIDEBAR – Monarch Butterfly Biosphere Reserve

In 1986, the Mexican government established a Monarch Butterfly Biosphere Reserve, to protect the monarch habitat from the detrimental effects of logging and development.  Since much of the area was privately owned by subsistence farmers dependent on logging income, deforestation continued.  New approaches were clearly needed.

Then, in 2001, the Mexican government in collaboration with Fondo Mexicano para la Conservacion de la Naturaleza (FMCN) and World Wildlife Fund (WWF), financed a trust fund designed to financially compensate local people for their lost logging rights in the preserve.  A contiguous corridor connecting the current butterfly sanctuaries within the forest was also established.