Butterfly on the Brink?
Monarch monitoring show their migration's in trouble.
By Rob McCorkle
Craig Hensley’s lifelong love affair with monarch butterflies began decades ago. He fondly recalls childhood days in Iowa lying on his back in a field and watching swarm after swarm of the delicate-looking insects fluttering overhead, some “cascading” down around him to fuel up on plant nectar for their long southward migration.
Today, Hensley, a Guadalupe River State Park interpretive ranger, has joined a growing chorus of experts warning about the fragile state of the autumn migration of millions of monarchs to their ancestral winter home in the mountains of central Mexico. The U.S. population of the resplendent orange and black butterfly has been suffering a precipitous downward spiral in numbers because of myriad environmental factors, many of them caused by people.
During the 20 years that Western scientists, many working for universities and butterfly monitoring organizations such as Monarch Watch and Journey North, have been keeping statistics on the butterfly’s 2,000-mile fall migration from Canada and the northern U.S. to the monarch’s winter roosts in Mexico, overwintering populations have fluctuated wildly. Populations that for two decades covered an average of 6.69 hectares of forest plummeted 82 percent in the winter of 2012, covering only 1.19 hectares, or just less than 3 acres. (A hectare equals 2.47 acres and is estimated to contain up to 50 million monarchs.) Early reports for the winter of 2013 look to be even worse coming out of Mexico, where monarchs overwinter in the oyamel fir forests in the Mexican states of Michoacán and Mexico.
Monarchs flock at their winter home in central Mexico.
“Monarchs are the new canary in the coal mine,” warns Cathy Downs of Comfort, an accomplished Texas Master Naturalist who spends most of her days spreading the dire news of the monarch’s plight to adults and schoolchildren alike. “It’s very possible that although monarchs may not become extinct in our lifetime, we could lose the migration.”
One of Downs’ mentors and one of the most respected voices in the Texas monarch community is retired cardiovascular surgeon Kip Kiphart, who lives just outside Boerne and travels the state lecturing on Danaus plexippus and providing monarch training. On a chilly, mid-October morning at the historical peak of the fall monarch migration, the affable naturalist joined a handful of volunteers for a butterfly count at Guadalupe River State Park led by Hensley. Texas plays a key role in the life cycle of the monarch, the official state insect of Texas. Both the fall and spring migrants of the monarch population east of the Rockies funnel through the heart of the state on their way to and from central Mexico’s Transvolcanic Mountains.
“Hard freezes down in the wintering grounds in 2002 caused a huge loss of monarchs, which roost at 10,000 to 12,000 feet, in what is typically a dry season,” Kiphart explains. “Monarchs can tolerate temperatures down to 18 degrees if it’s dry, but if it’s raining and the mercury drops to below 32 degrees, they can freeze to death. That’s what happened.”
Over the next two hours at the state park, the intrepid group made its way from the riverside to a portion of a restored 230-acre native prairie. The former mountain cedar patch now sports a diverse array of wildflowers and dozens of native antelope horn milkweed. Milkweed serves as the sole plant species upon which monarchs lay their eggs and upon which their offspring feed.
The morning’s resulting tally included a number of different butterfly species (Texas has 450 species), but only one monarch that Kiphart spied through binoculars hitchhiking with a flock of kettling white pelicans winging south. Kiphart pointed out that by this time the previous year, he had already “tagged” 800 monarchs, but could claim only 97 taggings this time.
Tags help researchers follow monarch movement.
Fred Urquhart of the University of Toronto first experimented in 1937 with tagging monarchs to try to track their movements. Today, hundreds of Texans net monarchs to attach an adhesive, dime-sized tag printed with a unique number to the butterfly’s hind wing. Those who find one of the tagged monarchs (in Mexico, it brings a $5 bounty) can call an 800-number or go online to report their find to Monarch Watch, a monitoring organization.
Longtime monarch researcher Lincoln Brower of Sweet Briar College in Virginia attributes the monarch decline of the past few years primarily to severe weather, but the overriding consensus of opinion points to habitat loss as the most insidious, long-term culprit. Native grasslands in Canada and the Midwest are being planted with soybean and corn — mostly genetically modified, herbicide-tolerant crops. Corn grown for ethanol production is also helping drive the loss of habitat. Sixty percent of the grassland ecosystem’s milkweed has been wiped out because of the introduction of herbicide-tolerant crops and conversion of land to biofuel crops.
California hosts a separate population of monarchs, which spend winters clustered in eucalyptus trees and Monterrey oaks and pines along the coast. There, the removal of aging trees and ongoing development are accelerating habitat loss. In the U.S., 6,000 acres a day fall victim to urban sprawl and development.
In Mexico, habitat destruction resulting from illegal logging, crop burning and fragmentation of monarch overwintering sites for subsistence farming continues to take its toll. While the Monarch Butterfly Biosphere Reserve, a World Heritage Site, boasts official protection status, the land is divided into more than 100 private properties (many of them ejidos, or communal agricultural lands), complicating management issues and fragmenting conservation efforts. Water diversion from overwintering forests and a high number of tourists also degrade monarch habitat. Biological impacts, such as mistletoe infestations in Mexico’s host trees, butterfly parasites and disease, also add to the volatile mix of negative developments affecting the iconic insect.
What is it about the monarch in particular — one of the world’s 20,000 butterfly species — that commands such awe and respect?
“It’s no one thing,” suggests Mike Quinn, a former TPWD invertebrate biologist also known as the “butterfly guy.” “They’re large, showy, easily identifiable insects whose seasonal appearance in your garden is fairly predictable. They’re nationally and internationally acclaimed for their annual mass migrations and their mysterious navigational abilities.”
Quinn, who has coordinated the Texas Monarch Watch since 2000 and hosts the online Austin Butterfly Forum, points out that because of the monarch’s distinct metamorphoses (four changes in form) and unique migration, the species serves as a classic teaching model. Educators often use the monarch to teach biology, chemistry, physics, geography and other academic subjects.
In Mexican folklore, some indigenous peoples marveled at the seemingly magical appearance of the butterflies in their communities each fall and winter. The butterflies’ annual arrival in alpine villages toward the end of October and first week of November, when Mexico celebrates the Day of the Dead (Nov. 2), led to a common belief that the monarchs were the returning souls of their ancestors.
Though most publicity centers on the fall migration, the returning spring flight north is also critical to the species’ survival. Master Naturalist Downs notes that in the spring, monarchs migrate through Texas on three major flyways, “nectaring and laying eggs along the way.” Successive generations make their way north, and it is the fourth generation of monarchs that makes it to the northernmost range in Canada and later migrates to Mexico.
On their northward journey, monarchs depend exclusively on about 30 different North American milkweed species, predominantly common milkweed (Asclepias syriaca), upon which to lay their eggs. Resulting larvae feed on the host milkweed. Emerging butterflies depend on various wildflowers, such as pentas, lantana and mistflower, for nectar on their northward journey to summer breeding sites. The leading edge of migrating monarchs typically begins reaching South and Southwest Texas in the first part of March, spreading into Central and North Texas later in the month and into April.
Monarch movement can be viewed on the Annenberg Foundation’s Journey North website (www.journeynorth.org). The program involves 785,000 student observers at 29,500 sites across North America. A number of those volunteers maintain and monitor monarch “way stations.” Butterfly gardens planted with nectar sources and, in some cases, milkweed can be found on both private property and public property such as schools and parks.
Monarchs migrate in the spring and fall, spending summers in the northern U.S. and Canada and winters in Mexico. In spring, monarchs lay eggs along the way. An egg hatches into a caterpillar, which later forms a chrysalis and emerges as a butterfly.
More than 6,000 way stations have been established in Texas. Many of those sites are involved in the nationwide Monarch Larva Monitoring Project begun in 1996. The Texas Parks and Wildlife Department offers a “Butterfly Garden” brochure with suggested nectar and host plants. Information about establishing a Texas wildscape that benefits all wildlife can be found by visiting www.tpwd.state.tx.us/wildscapes.
Milkweed, which is not an especially attractive plant, often succumbs to the garden hoe or highway department mower. Because milkweed contains a toxic compound absorbed by feeding monarch larvae, the emerging black, yellow and white striped caterpillars feeding on its foliage rarely become a meal for birds or other predators.
Planting milkweed is considered the most important step Texans can take to help monarchs. The three most common native milkweed species found in Texas are antelope horn, green antelope horn and zizotes. Challenging to propagate from seed, which is sold by a handful of Texas growers such as Native American Seed in Junction, milkweed has become commercially available as small plants in a few select nurseries. Consumers should be careful to make sure that the more readily available tropical milkweed and butterfly weed, with their attractive flower clusters, have not been sprayed recently with pesticides. This can be deadly to monarchs.
The real key to the survival of the miraculous monarch migration, however, lies with gaining an even better understanding of existing threats and sounding the clarion call about the creature’s delicate dance on the edge of extinction.
Those interested in learning more can attend lectures and workshops listed online by TPWD on the Texas state park events pages, the Texas Master Naturalists and various butterfly forums.
“If I can leave you with one message,” inveterate monarch crusader Downs told attendees at last September’s workshop in Kerrville, “it is this: Teach the children.”
» Monarchs have a typical wingspan of more than 3.5 inches and an average weight of 0.5 grams (about that of a paper clip), among the largest of North American species.
» A single monarch female can lay up to 300 to 400 eggs.
» An adult’s lifespan ranges from one to nine months. » Migrating monarchs can cover an average of 25 to 30 miles a day.
» Most monarchs joining fall migration are three to four generations removed from those that made the previous year’s journey.
» In order to grow and develop, monarch caterpillars need milkweed plants; they can increase their weight almost 3,000 times in 10 to 15 days.
» Monarchs are notably promiscuous, with lifetime mating frequencies of about eight for each sex.
» Monarchs contain a group of compounds known as cardiac glycosides, acquired by monarch larvae feeding on milkweed, that provide protection by inducing vomiting in many vertebrates.
» Like birds, monarchs conserve energy by catching updrafts of warm air, called “thermals.” Upon reaching the thermal top, they glide toward their destination.
» There are two North American populations of monarchs divided geographically by the Rocky Mountains.
» The eastern monarch population migrates each fall to Mexico, while a western population overwinters in coastal forests from California’s Mendocino County south to Baja while moving inland in the spring to breed.
» Monarchs overwinter in dense clusters of alpine oyamel firs in a semi-dormant state, living off stored fats.