Gardeners save the day as butterfly habitats disappear
Monarchs rapidly losing breeding ground, but a small plot of milkweed in yard or on the roof can help save them
The San Francisco Chronical Deborah K. Rich, Special to The Chronicle Saturday, February 17, 2007
For $16 worth of seeds, plus space and time, gardeners across the country can counter the precipitous loss of monarch butterfly habitat that has occurred in the past 10 years because of the spread of genetically engineered crops, urbanization and global warming.
“It has become increasingly evident that we have a major conservation crisis,” said Orley “Chip” Taylor, professor of entomology at the University of Kansas and director of Monarch Watch.
Monarch Watch began in 1992, to inform the public about monarchs. The group has also conducted a monarch-tagging program involving 100,000 citizen scientists.
Two years ago, however, Taylor felt compelled to add a new element to Monarch Watch’s mission, that of developing a nationwide network of monarch habitats, or way stations, to help stanch the rapid loss of monarch habitat.
Last year, Monarch Watch began offering a seed set of milkweeds and nectar plants suited to California. “We need way stations everywhere here in California in the monarchs’ summer breeding area, which begins just east of the coastal fog belt,” said Mia Monroe, volunteer monarch coordinator for the Xerces Society, which is dedicated to invertebrate conservation. “We need them throughout the greater Bay Area in Palo Alto, Novato, San Rafael, Lafayette, Oakland; up and down the Central Valley; and over on the eastern side of the Sierra.”
Taylor said: “Every migratory species needs patches of habitat where there are resources, and for monarchs that habitat has basically been patches spread across the whole continent. But now we have big holes out there where we just don’t have any habitat at all for butterflies.”
In the United States, there are two distinct groups of monarchs: an eastern population and a western population. The eastern population breeds east of the Rocky Mountains, and migrates to the oyamel fir (Abies religiosa) forests in the Transvolcanic Mountains of central Mexico each winter. The western monarch population breeds in areas west of the Rockies and spends winters along the California coast, clustering in stands of eucalyptus trees, Monterey pines and Monterey cypresses.
The decline in the eastern monarch butterfly population can be tracked by measuring the area the butterflies occupy in Mexico. Whereas eastern monarchs spread out over millions of acres during the summer, they cluster in a very small area in the winter.
“In the winter of 1996-1997, monarchs occupied 21 hectares in Mexico,” said Taylor. “The highest we’ve seen in the last 10 years is 12 hectares.” (One hectare equals approximately 2.5 acres.)
The western monarch spends winter in hundreds of sites strung along the California coast, from Sonoma down to Baja California, making it difficult to estimate population. Still, the trend is steadily downward.
“You go to the more well-studied sites like Pacific Grove, or Natural Bridges, or Pismo Beach, and there was a time when you would see 10,000, 40,000, 80,000 monarchs. And now you see maybe 4,000, 8,000, 10,000,” said Monroe, who is also park manager of Muir Woods National Monument.
“At the edges of their winter ranges, there are now years where there are very few to no monarchs. In the 1980s and 1990s, even these fringe sites would have had thousands of monarchs.”
A primary cause of eastern monarch habitat loss is the near-complete conversion of the United States’ 75 million-acre soybean crop to ‘Roundup Ready’ soybeans over the past 10 years. These soybean and corn varieties, genetically engineered and owned by the Monsanto Co., are able to withstand repeated applications of glyphosate, an herbicide that causes most species of green plants to die back by disrupting the production of amino acids essential for plant growth.
The corn and soybean fields of the Midwest once provided about 50 percent of the eastern monarch’s breeding ground. Monarchs congregated in these fields to lay their eggs because of the presence of various species of milkweed, especially the common milkweed (Asclepias syriaca), which grows well where soils are disturbed annually.
Monarch larvae, or caterpillars, are specialist herbivores, and the only thing they’ll eat from the moment they are born until they form a chrysalis is milkweed. By providing millions of acres of fertile ground for milkweed to grow on, agriculture, in a sense, helped support eastern monarch populations, despite its efforts not to. Some milkweed varieties are designated as noxious weeds, and farmers have long used pre-emergence herbicides (those sprayed on fields before crop seedlings emerge) and cultivation to control them.
“Farmers used to spray Roundup early on, but milkweed actually emerges fairly late, and Roundup is a contact herbicide,” said Karen Oberhauser of the Department of Fisheries, Wildlife and Conservation Biology at the University of Minnesota.
“The farmers would also disk their fields once the crop was 6 to 10 inches tall, but that didn’t really kill the milkweed; it set the milkweed back a bit, but milkweed has an underground rhizome-like structure, and the milkweed would just start right back growing after cultivation.”
In 2000, Oberhauser organized a formal count of milkweed in the Midwest, just before farmers began widespread use of ‘Roundup Ready’ crops.
Today, milkweed has all but disappeared from Midwestern agricultural fields. “I’ve gone back to the fields that I studied in 2000, and basically the milkweed is gone,” said Oberhauser.
‘Roundup Ready’ crops aren’t as pressing a threat to the western monarch population. California grows relatively little field corn and virtually no soybeans. California also lacks the common milkweed of the Midwest. Milkweed native to California tends to grow better in undisturbed soils, depending more upon native habitats and roadsides than on agricultural fields.
Unfortunately, undisturbed land is rapidly growing scarce in California. “All you have to do is look at a map of California every 10 years and see that there are tremendous natural areas that are now suburbia, which means milkweed and native nectar plants aren’t as present; that the number of roads is increasing, and each road is a hazard for monarchs to cross; that the amount of natural surface water is decreasing. All these things are a hazard to any creature, but especially one like monarchs that rely upon plants, water and open space,” said Monroe.
In California’s Central Valley, prime summer breeding ground for the western monarch, more than 27,000 acres were urbanized just between 2000 and 2002. Meanwhile, many of the western monarch’s wintering sites are on private land along California’s coast and subject to intense development pressure.
Global climate change is expected to further habitat loss for both the eastern and western monarch populations by making their wintering site in Mexico wetter, and their California and Midwestern breeding grounds hotter.
Oberhauser has modeled the likely future climate scenarios on the forests of central Mexico. Her findings show that the monarch’s wintering grounds will not become warmer but will become wetter, thereby increasing the likelihood of rain coinciding with freezing temperatures. Monarchs can withstand either wet or cold weather, but when the two occur together, monarchs suffer “catastrophic mortality.”
In 2002, a combination of 48 hours of heavy rainfall followed by a drop in temperatures to 26 degrees Fahrenheit killed 80 percent of the overwintering butterflies. “There were places where the ground was knee-deep in butterflies,” said Taylor of Monarch Watch.
Oberhauser has also modeled likely climate scenarios in the eastern monarchs’ summer breeding areas. Her studies show that the Midwestern states will probably become too hot for monarchs, forcing the monarchs to migrate ever farther north during the summer. When the temperatures hover for long in the mid-90s and above, eggs and larvae suffer higher mortality, adult monarchs live shorter lives and milkweed begins to dry out, becoming a poorer food source.
Whether or not the eastern monarch will be able to extend its annual migration into Canada is unknown. Unknown, too, is whether the milkweed will be there to receive their eggs. “Generally plants don’t migrate as quickly as animals,” said Oberhauser.
The forecast doesn’t bode well for monarchs in California either. Predicted increases in summer temperatures of 3 to 10 degrees in the Central Valley will affect a large portion of the western monarchs’ breeding grounds, and to the extent that climate change increases the intensity of winter storms and winds along the California coast, their coastal habitat will suffer also.
Aligned against this triple threat to monarch habitat is a small but growing cadre of gardeners recruited by Monarch Watch. In April 2005, Monarch Watch began enlisting gardeners across the United States to create “monarch way stations” to start bridging the gaps in monarch habitat. “Loss of habitat is pinching all species. It’s hard to figure out how to help the larger species, but for the butterflies there is something we can do,” said Taylor. “The individual citizen can do a lot.”
Way stations consist of patches of nectar plants (for the adult butterflies) and milkweed plants. A network of these simple way stations strung together across the continent can give the monarch a fighting chance for robust survival, even in the face of loss of millions of acres of habitat. “The monarch has an incredible capacity to find even small little patches of habitat. So if you create even a rooftop garden, just with plants in pots, it’s extremely likely that a monarch butterfly will come through there and lay eggs on the milkweeds, and sip nectar from the nectar plants, and use that rooftop as a habitat,” said Taylor.
Monarch Watch has developed a $16 way-station seed set of six milkweed species and six nectar plant species. (The number of seeds sent per plant variety ranges from 20 to 100 seeds.) Species include a mixture of annuals and perennials, and none of the varieties are invasive. The way-station seed sets work for home, school, park and business center gardens, as well as for field edges, roadsides and other vacant land.
Monarch Watch maintains a monarch way-station registry of qualifying habitat gardens to keep track of the growing network. To apply, way-station gardeners complete a questionnaire about the number and types of plants in their way stations, and their methods of fertilizing and irrigating (with sustainable practices encouraged). The registry is open to all way-station gardeners, whether they purchased seed from Monarch Watch or from another source.
Over the past two years, Monarch Watch has mailed out 3,000 seed packets and has registered 1,059 monarch way stations. Monarch Watch’s goal is to register 10,000 way stations in three years. “We can change some negative impacts we’re having on the environment by doing some fairly simple things,” said Taylor. — Note: Milkweed does best in well-drained soil. Clay soils should be amended. Start seeds indoors or plant them directly in the soil after the last frost. The milky sap of milkweed is toxic to humans and pets. It is very bitter, however, so it is unlikely to be consumed in large enough quantities to cause a problem.
New hybrid corn less of a threat to monarchs Despite initial fears, pollen from corn engineered to be toxic to many lepidoptera (butterflies and moths) larvae has proved harmless to monarch butterflies.
But that’s not to say that the fears were unfounded. In 1999, Cornell University researchers published studies that demonstrated that pollen from the Bt corn varieties then on the market contained doses of Bt toxin that were highly lethal to monarch larvae. The study raised the concern that pollen from Bt corn plants would drift onto milkweed and be consumed by monarch larvae (caterpillars), which depend upon milkweed for sustenance. When the study was released, milkweed and monarchs were commonly found in and around Midwestern corn fields during the summer, and Midwestern corn and soybean fields provided at least 50 percent of the eastern monarchs’ summer breeding habitat.
Fortunately for monarchs, these early Bt corn varieties proved to have poor agronomics, which prevented their widespread commercialization and adoption.
Subsequently released varieties of Bt corn performed better for farmers and happened to have a much less lethal dose of Bt toxin in their pollen.
A study released in 2004 did find, however, that fewer monarch larvae survived in Bt cornfields than non-Bt fields when monarch larvae were exposed not only to Bt corn pollen but also to anthers from Bt corn.
Though this latter study suggests that the effect of current Bt corn varieties on monarch larvae is still not benign, a larger threat to monarchs from genetically engineered crops has arisen with the widespread adoption of corn and soybean varieties engineered to withstand repeated applications of herbicides.
With the ability to repeatedly spray potent herbicides that cause every plant but the engineered corn and soybean to die back, farmers have almost completely eliminated milkweed from Midwestern agricultural fields. — D.K.R.
Monarch Watch To learn more about Monarch Watch’s education outreach, butterfly tagging and way-station program, go to www.monarchwatch.org, or write Monarch Watch, University of Kansas, 1200 Sunnyside Ave., Lawrence, Kan. 66045-7534. Telephone: (888) 824-4464 or (785) 864-4441.
To purchase a monarch way-station seed kit, go to shop.monarchwatch.org. Click on “more” under the icon for the Monarch Way Station Seed Kit. A drop-down menu will give you the opportunity to select the California way-station seed kit.
Monarch Larva Monitoring Project: Karen Oberhauser at the University of Minnesota invites individuals to join the Monarch Larva Monitoring Project. Since 1997, the project has enlisted volunteers to collect data on monarch larvae. It is a “citizen science” project, and anyone with access to land with milkweed can participate. Visit the Web site at www.mlmp.org.
Peterson Middle School Nature Area: For more information about the Peterson Middle School Nature Area, or to arrange a field trip to the site, go to peterson.ca.campusgrid.net/home. On the left-hand side of the screen, click on “Nature Area, Cams, & News.”
Monarch butterfly cycle of life A monarch butterfly begins life as a tiny egg, above, which hatches into a caterpillar, right. After the caterpillar grows to its full size, a protective shell, or chrysalis, forms around the insect, below right. Its transformation into an adult occurs in this resting stage. Finally, the shell breaks open and the butterfly emerges (below), flying off to find a mate and start the cycle anew.
Source: World Book Encyclopedia