Habitat loss imperils monarch butterflies’ migration

By Wayne Savage

 

The leading edge of monarch butterflies’ annual spring migration is passing through the Washington area after their winter colonies in Mexico shrank to the smallest size ever recorded.

Observers in the Washington area reported initial sightings of the iconic insects on May 2 at the Winkler Botanical Preserve in Alexandria, Va.; on May 3 in a backyard garden in Fairfax, Va.; and on May 5 at the Beltsville Agricultural Research Center in Beltsville, Md. The sightings are recorded at The Journey North, a website where citizen-scientists report observations of migratory birds and other species.

 

3,000-mile migration

 

During spring and summer, monarchs breed throughout the United States and southern Canada, although the prime breeding areas are in Texas, Oklahoma, Arkansas, Kansas, and the upper Midwest.

In the fall, monarchs from east of the Rocky Mountains migrate to Mexico, fl­ying up to 3,000 miles to remote overwintering sites among fir trees in the Sierra Madre Oriental Mountains of central Mexico. The Mexican government has created a “biosphere reserve,” now encompassing 217 square miles, to protect the monarch colonies.

Monarchs are known to breed year-round in South Florida, and some can survive winters along the northern Gulf Coast if temperatures remain mild. But many monarchs arriving on the Florida panhandle attempt to reach Mexico by flying 700 miles non-stop across the Gulf of Mexico, according to Richard G. RuBino, professor emeritus of regional planning at Florida State University.

“[T]hey are often seen clinging to the decks of fishing boats, pleasure boats, and on oil platforms many miles away from shore,” Rubino said in a report published by Monarch Watch, a nonprofit educational program at the University of Kansas.

In the spring, the monarchs that overwinter in Mexico fly north to lay eggs on milkweeds and a few other plants in the dogbane family. Milkweed leaves are the only food source for monarch larvae (caterpillars) and thus essential to the butterfly’s successful breeding.

The total area covered by monarch colonies last winter in Mexico was just 0.67 hectares (1.66 acres), according to the World Wildlife Fund-Mexico. It was the third straight winter of colony shrinkage for the monarch and the smallest area covered by the overwintering colonies since they were first discovered in 1975. The largest colonies occurred in 1996-97, when 20.97 hectares (51.82 acres) were covered.

“The monarch butterfly as a species is not endangered,” said Omar Vidal, director general of WWF-Mexico, in an email exchange with Nationalgeographic.com on Jan. 29. “What is endangered is its migratory phenomenon from Canada to Mexico and back.”

 

Loss of habitat

 

Multiple factors on both sides of the U.S.-Mexican border have converged in recent years to decimate the monarch population.

Illegal logging deforested or degraded 2,057 hectares (5,081 acres) of habitat in the Mexican monarch reserve from 2001 and 2012, Vidal reported. Enforcement efforts and the creation of alternative income sources for local residents have halted large-scale illegal logging, but small-scale logging remains a concern.

In the United States, milkweed has suffered from the widespread use of the herbicide glyphosate (e.g., Monsanto’s Roundup brand), especially after the introduction in 1996 of genetically engineered crops that are resistant to it. Application of glyphosate to control weeds replaced mechanical tillage, a traditional practice that allowed some milkweed plants to survive, according to Orley R. “Chip” Taylor, director of Monarch Watch.

Milkweed took another hit in 2007 when the federal Renewable Fuel Standard required blending biofuels, such as ethanol distilled from corn, into petroleum-based fuels. That led to a surge of corn and soybean production, displacing millions of acres of milkweed habitat. Between 2006 and 2013, the number of acres planted in corn and soybeans grew from 153 million to 174.4 million, a 14-percent increase due largely to the ethanol mandate, Taylor wrote in a January blog post on the Monarch Watch website.

Native prairies, rangelands, wetlands, and 11.2 million acres of land previously in the federal Conservation Reserve Program have been plowed under to produce more corn and soybeans, according to Taylor.

The ethanol mandate also spurred farmers to plant the edges of fields that had provided a safe niche for milkweed.

“It took us 40 years to end edge tillage in this country, and overnight ethanol brought it back with a vengeance,” said James Conca, a columnist for Forbes.com, in an April 20 commentary.

Taylor estimates that another 17 million acres of land east of the Rockies – much of which contained milkweed at one time – has been lost to development due to human population growth since 1996.

The monarch population will rebound, in Taylor’s view, only if weather conditions are favorable and there is enough milkweed. He grimly predicts that the large numbers of monarchs of the 1990s will never return.

Fairfax resident aids

monarchs’ ‘cycle of life’

 

Numerous organizations are working to encourage milkweed cultivation and habitat conservation, an effort that includes backyard gardeners such as Marbea Tammaro of  Fairfax, Va. She grows milkweed at her home and reported a May 3 monarch sighting to The Journey North website.

Tammaro, an occupational therapist with Arlington County public schools, said she started growing milkweed two years ago after taking a class through the Monarch Teacher Network, an organization that helps teachers incorporate information about monarchs into their curricula.

After sighting the monarch flitting around her milkweed plants, which are in a warm location facing south, Tammaro returned a short time later and discovered 60 pinhead-size eggs laid on the leaves.

It’s unlikely that the monarchs arriving in Washington came all the way from Mexico. Instead, they probably are first-generation descendants from individuals that overwintered in Florida or Mexico.

“I thought that she looked very young,” Tammaro said of the monarch at her house on May 3. “Not faded, not beat up … no visible tears or breaks.”

Tammaro’s concern for monarchs includes rearing them indoors, safe from the birds that prey on caterpillars.

“When I find eggs,” Tammaro said, “I protect them outside or take them into my house and raise them where they get what they need but are protected from predators.”

After maturing for three to five days, the monarch eggs hatch caterpillars that molt several times before forming chrysalides that turn into adult butterflies. Throughout the entire process, which takes about four weeks, Tammaro provides milkweed from her garden, placing the greenery in containers of water as one would a bouquet of flowers. To contain the older caterpillars and adults, Tammaro constructs rearing cages made of steel tomato cages turned upside down and covered with a thin mesh material.

The ravenous monarch caterpillars eat the milkweed leaves down to the stalk.

“When you’re around them and it’s quiet, you can hear them munching,” Tammaro said. “It’s really funny.”

After emerging from their chrysalides, the adult monarchs dry their wings for a couple of hours by periodically flapping them, then are ready for release into Tammaro’s garden, where nectaring plants, or fruit juice or orange slices, await.

“I try to let them go in the early part of the day in a sunny day so they can find food and get to a safe place … rather than when it’s dark and raining,” Tammaro said.

Tammaro admits that her children think her interest in monarchs is a bit nerdy, but she encourages others to cultivate milkweed, which grows easily, and said monarch husbandry is a way to be part of the cycle of life.

 

Update (Feb. 27, 2016): World Wildlife Fund reports monarch populations in Mexico are up significantly this winter. See the Reuters news story here:  http://www.reuters.com/article/us-butterflies-monarchs-idUSKCN0VZ2YA

 

Wayne Savage is the owner of Mid-Atlantic Litter Cleanup Service, a Washington, D.C.-based litter-removal service.  He co-owns a small tract of land enrolled in the Conservation Reserve Program in central Missouri.

 

For further information:

Monarch Butterfly Fund:  www.monarchbutterflyfund.org

The Monarch Butterfly in North America (USDA):

www.fs.fed.us/wildflowers/pollinators/Monarch_Butterfly/index.shtml

Monarch Joint Venture: http://www.monarchjointventure.org