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As the days grow shorter and fall approaches, newly emerged monarch butterflies become restless. Although the bright orange- and black-winged insects currently visiting backyard flowerbeds may appear identical to those seen earlier in the summer, they are biologically different from all others. The group of adults currently flittering about are so unusual that scientists give them a special name—this year’s final crop of young are the annual super generation.
Unlike their predecessors, whose entire life cycle could be measured in mere weeks, super generation monarchs complete a 3,000-mile-long migration marathon, acquire the remarkable ability to halt aging and then stay alive for more than eight months—the rough equivalent of a human living six centuries.
The annual cycle begins high in the remote volcanic mountains of central Mexico. With the arrival of spring, monarchs that hatched the previous summer in Canada and then migrated to Mexico last autumn suddenly respond to the irresistible call to move north. But their second migration will be brief and adults will never see their Canadian homeland again. Arriving on the plains of Texas, the ancient insects pause to mate, lay eggs and die.
Caterpillars emerge, grow, form chrysalises, and become adults. Second-generation butterflies continue the flight north. Soon they, too, will stop to mate, lay eggs and die. The cycle continues until, four or five generations later, in a few months, monarch butterflies began appearing in Iowa. The airborne relay race continues until, sometime in August, the species reaches its final destination on the Canadian prairies.
Arriving at the relay’s northernmost finish line, these adults are the great-great-great-grandchildren of the monarchs that left Mexico just four to five months earlier. It is their offspring that become super monarchs, that unique generation that embarks on one of the animal kingdom’s most incredible journeys.
Unlike previous generations, super monarchs do not mate or lay eggs right away. Instead, they devote all their energy to feeding. Their only interest is to drink nectar and build fat reserves for the grueling task ahead.
But the seasonal clock ticks with little time to waste. Within days of emerging as adults, the super generation begins to move southward. Not just in a general southerly direction, mind you, but rather on a specific and well-defined course that leads to the exact same winter roost trees used by their great-great-great-grandparents the winter before.
Taking advantage of favorable breezes, monarchs travel 50 to 60 miles per day, taking time to replenish spent fuel reserves as they continue to gain weight during migration. The flight is not without casualties. Losses from storms, unexpected frosts and highway traffic exact a deadly toll.
Unlikely Oasis Provides Monarch Sanctuary
To a casual passerby the spot would likely appear insignificant, if it would even be noticed at all. Just a scraggly cluster of 20 ash trees, with most reaching less than 20 feet in height. Located in the heart of the 2,200-acre prairie wetland complex of the Union Hills Waterfowl Production Area in Iowa’s Cerro Gordo County, the volunteer trees are the last reminder of a long abandoned homestead.
But first impressions can be deceiving. During fall migration this apparently inconsequential grouping of “weed trees” serves as a butterfly oasis. Overnight, this seemingly unlikely spot becomes temporary host to one of the region’s greatest natural wonders as a monarch roosting area.
The transformation begins as the annual super generation of migrating monarch butterflies arrives from Canada. Attracted by more than 2,000 acres of nectar-producing goldenrod, blazing star, and other late blooming prairie plants, the Monarch hordes pause to take on fuel before continuing the rigorous journey to central Mexico’s Sierra Madre mountains.
Following a full and exhausting day of migration and feeding, the colorful insects assemble at the roost during late afternoon and then spend the night in deep, torpor-like sleep. The migration begins with just a handful of butterflies checking in for the night. But soon dozens become hundreds, hundreds become thousands.
Numbers may fluctuate dramatically. It’s early September, and this year’s flight is approaching its peak. Yesterday the roost contained just shy of 4,000 migrating monarchs. This morning, there are more than 5,000.
Resting wingtip to wingtip, there are so many butterflies here you can almost feel them breathe. But the silence is deafening. The sun is just coming up and it is so still—so incredibly quiet. For those used to photographing birdlife, and surrounded by their songs, it is utterly amazing to be surrounded by so much life and yet so much silence at the same time.
Photographing the experience is humbling. It doesn’t take long to realize the task is impossible. Although photography is a great communications tool, this is one of those moments when no photo can do the scene justice. In this case, there is simply no substitute for being here.
Migrating To Mexico
The sun has cleared the horizon now and, influenced by its warming rays, the waking monarchs begin to slowly flex their wings. A half-hour later, the first individuals break from the orange clusters and take to the air. Unlike birds, there is no organized flocking. Instead, each butterfly randomly flits in the direction of the yellow and purple flowers that dot the prairie landscape. The numbers increase until the sky fills with monarchs. For this year’s super generation of monarchs, a new day of migration has begun.
As the migration moves southward, the pathway narrows. Survivors concentrate and merge into huge butterfly clouds that fill the skies like orange glitter. Finally, following more than two months of rigorous travel, the super generation arrives in Mexico. With frayed wing edges and missing scales, many appear tattered and worn, while others appear largely unscathed.
But the monarch’s epic journey is not yet complete. One final and seemingly impossible hurdle must be conquered before the insects can finally rest. That challenge is to reach the perfect winter climate found solely among the high elevation, mountainside firs that stand more than 10,000 feet above sea level.
The task is daunting but crucial. Winter is fast approaching and no monarch eggs, caterpillars or adults remain to the north. For weary migrants, the only chance of survival lies in successfully reaching the perfect environment of the volcanic forest.
The future of the species hangs in the balance. Everything is now staked on the worn, four-inch wings of those who have made it this far. The butterflies begin their ascent and within days begin filtering into the two-mile-high winter roosting sites of their ancestors. Home at last to a place they‘ve never been, the super monarchs slumber until lengthening spring days rekindle the age-old urgency to move north and lay eggs on the leaves of milkweed plants, giving birth to another generation.