It's late September 28 and I'm on the Blue Ridge Parkway doing what I always do when I can get out of the house. I'm observing and photographing nature. Several weeks earlier I had experienced the colorful explosion of summer's showy roadside wildflowers, and a few weeks from now I'll be back to take pictures of the autumn color show. Early this morning, I watched a spectacular sunrise from Pounding Mill Overlook. Mountain ridges rose above fog-filled valleys warmly illuminated by the rising sun. But none of these events-indeed, few things in nature-can compare with what I'm seeing right now.
I'm watching Danaus plexippus, the monarch butterfly, bounce with the wind as it passes above the ridge at Tunnel Gap on its annual migration. I saw the first monarch around 10:00 this morning and by 2:00 this afternoon I had counted 87. I greet each sighting with the same awe and wonder as if I'd just seen a butterfly for the first time in my life. Admittedly, there's nothing particularly fascinating about seeing a butterfly fly over a gap some a hundred feet over your head. But when you contemplate where that butterfly might have come from and then consider where it's going, "awe" and "wonder" barely describe the emotion felt.
Some of these butterflies, seemingly struggling to get over just this single mountain ridge, started their journey as far away as Canada and won't stop until they get to Mexico. Yes, these delicate little creatures-each weighing about the same as a postage stamp-travel nearly 3,000 miles! What's more amazing is that no single monarch butterfly makes the full migration. The butterflies I'm watching at Tunnel Gap may have come from Canada and will continue flying to Mexico, but it's their descendants who will complete the cycle and return to Canada. And no one knows exactly how they do it.
Around late August in southern Canada, the butterflies' biological clocks start cuckooing and they begin their long journey. They navigate by using the angle and intensity of sunlight and perhaps magnetic fields. Like floodwaters rising with the influx from side streams, the mass butterfly exodus grows as it travels southward. The insects pass through North Carolina from about late September to early October, joined by local residents along the way. Utilizing air currents to enable their long flight, the butterflies reach the Transvolcanic Mountains of central Mexico by late November. There, the butterflies roost nightly in oyamel fir trees at an elevation of around 9,000 feet. Depending on the particular roost site, there may be tens of millions of butterflies in an area of only a few acres. Butterflies cover the trees entirely, with branches sometimes breaking off from the excessive weight. During the day the butterflies leave the roost to get a drink of water and perhaps sip nectar from wildflowers. There are so many butterflies flying around that tourists visiting the sites have to be careful to keep from inhaling them! Hundreds land on the visitor's clothes and hair.
Sometime in late February, the biological clock starts cuckooing again. The butterflies begin the mass exodus north, following emerging milkweed plants along the way. The females lay a few hundred eggs on the milkweed over a period of a couple of weeks. Then, exhausted, they die. In about four days the eggs hatch into the larval stage, the familiar caterpillar. Caterpillars do little more than eat and molt. After five molts over a period of 9 to 14 days, the caterpillar glues itself upside down from a twig or leaf. Now the butterfly enters the pupa stage, also called the chrysalis. (Although some people use the term cocoon and chrysalis interchangeably, a cocoon technically is the pupa stage of a moth.) During the pupa stage, the larva metamorphoses into an adult monarch butterfly. Upon emerging from the pupa, the butterfly expands its wings and lets them dry for several hours. Once the butterfly takes flight, it resumes the journey north. It finds a mate and begins the cycle again.
After several generations the monarch is home, completing the migration cycle that began the previous year. The final generation does not mate, but is the one who starts the cycle over. How does a butterfly up to four generations removed from the original journey know to begin again? How does it find its way to the same location-and often the same tree-that its great grandparent roosted in the previous winter? Scientists continue to grapple with these and other questions. We may never know the answers.
Considering the obstacles, it's remarkable that any butterfly makes it to Mexico and back regardless of the number of generations it takes. Cardiac glycosides give the monarchs a built-in natural chemical defense against most predators, but a few species of birds and mice seem unaffected and consume them in great numbers, particularly at the overwintering sites. Other natural obstacles include parasites and disease from viruses and bacteria. Abnormally cold weather at the overwintering sites can cause severe population declines; during the severe snowstorm of 2002, an estimated quarter-billion monarch butterflies froze to death. Cold weather during the breeding season causes a lower number of breeding generations, which drastically alters populations.
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Despite all these natural obstacles, humans cause the biggest problems by far. Logging and agricultural practices at the overwintering sites presents possibly the greatest dangers, but habitat destruction in the states is also a major factor. Pesticide spraying kills not only target species but monarchs and other insects as well, and herbicides kill milkweed and nectar plants. Sadly, some combination of all these factors has resulted in record-low numbers of monarchs at the overwintering sites during the 2004-05 season.
This gloom and doom doesn't mean we will soon lose one of nature's most intriguing creatures. Monarch butterflies have shown a remarkable capacity to survive and to rebound from even catastrophic events such as the 2002 snowstorm. Scientific research continues to expand our knowledge, while numerous organizations and concerned citizens-including many in North Carolina-work hard to ensure a future for the monarch by orchestrating tagging operations, planting milkweed, and educating the public.
Tagging butterflies is among the most rewarding and fun projects to undertake. And when one of "your" butterflies is discovered, it feels like you've won the lottery. Just ask Judy Carson of The Orchard at Altapass on the Blue Ridge Parkway. Eight years ago, Carson began raising and tagging monarchs. She tags about 100 butterflies each autumn. Remarkably, six have been recovered in Mexico. When you consider the odds that someone would discover a tagged monarch among the tens of millions of butterflies that make the journey to Mexico, Carson's tally is astonishing.
The Orchard at Altapass has always been a popular stopping point for tourists traveling the parkway, but since Carson started tagging monarchs her visitors have an enhanced experience. As she explains, "We're teaching our guests the importance of all critters on earth. Many people traveling the Blue Ridge Parkway are not familiar with the life history of the monarch butterfly and they get to learn that here and experience it for themselves."
Carson releases tagged monarchs from August until early October. Around the end of September or the first of October, she welcomes guests of all ages to participate in a formal tagging operation orchestrated by writer Elizabeth Hunter. Last year, a large crowd watched a two-year old boy stand motionless for ten minutes as a lethargic monarch butterfly crawled over his little hand while warming its wings. When the butterfly finally flew away, everyone cheered. Carson says it's not just children who enjoy the show. "Some of our senior citizens have been hooked and gone on to become the 'butterfly lady' of their town."
Tagging is fun and contributes to the scientific knowledge of the monarch, but you can do other things to help. Among the best things is to plant milkweed on your property or that of a friend or family member. With habitat loss being among the greatest threats to monarchs, planting their host plant helps their plight immeasurably.
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Anyone interested in monarch butterfly activities should visit www.monarchwatch.org or call 888-TAGGING or 785-864-4441. Begun in 1992 by entomologist Chip Taylor, Monarch Watch is an education outreach program of the University of Kansas. Taylor has done more to advance the scientific knowledge of the monarch butterfly than perhaps anyone has in past two decades. According to the web site, more than 100,000 students and adults participate in Monarch Watch tagging operations each fall. The web site provides everything you need to know to participate. It also provides detailed information about monarch biology, conservation, butterfly gardening and rearing monarchs, and specifics on how you can become involved with the protection of the wintering grounds in Mexico. Elementary school teachers might consider developing a monarch tagging operation as a class project. It's easy to do, tons of fun for the kids, and provides a terrific lesson in biology and conservation.
In addition to www.monarchwatch.org, there are a number of great web sites for monarch and general butterfly enthusiasts. Start by visiting the North American Butterfly Association's site at www.naba.org. North Carolina has its own organization called the Carolina Butterfly Society, which sponsors numerous field trips annually. Its web site at www.carolinabutterflysociety.org is especially useful as the information pertains mostly to North and South Carolina. Another great site is Monarch Lab at www.monarchlab.umn.edu. The Orchard at Altapass is located at milepost 328.3 of the Blue Ridge Parkway, near Little Switzerland. Call 828-765-9531 or visit www.altapassorchard.com.
I've spent a great deal of my life studying the natural history of North Carolina, and along the way I've taken tens of thousands of photos and witnessed some extraordinary sights. But I can't think of anything as remarkable as seeing a delicate little monarch butterfly in late September and knowing that in a month or so it might be among millions of others spending winter vacation in Mexico. Think about that the next time a monarch butterfly flutters your way.
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Scientific Research of the Monarch Migration
In the late 1800s, scientists knew that monarchs along the west coast migrated and overwintered in California. But it wasn't until the early 1970s that they had proof of an eastern migration. Dr. Fred Urquhart, professor of zoology at the University of Toronto, had started a tagging program in the late 1930s in which he applied wing tags imprinted with contact information and a code number specific to the butterfly. In the 1950s, Urquhart began utilizing the help of thousands of research associates across the country. By the early 1970s, they had accumulated enough information to know that monarch butterflies were flying to Mexico. Then, in 1975, a research associate discovered the wintering grounds. Urquhart's ensuing article in National Geographic attracted keen interest from numerous scientists.
In the 1950s, the country's preeminent monarch expert, Dr. Lincoln Brower, discovered that different species of milkweed contain different toxicities of the chemical cardiac glycoside. He also discovered a method to test for this chemical in adult butterflies. This procedure allowed him to determine upon which species of milkweed the caterpillar had fed. Since milkweed is the monarch caterpillar's only food source, and since the various milkweed species grow in different parts of the country, Brower could determine from where the butterfly had come. More recently, scientists have analyzed hydrogen isotope patterns to determine the origin of the butterflies.