EarthTalk / Monarch butterfly victim of summer heat, shrinking winter habitat
Published 12:21 pm, Tuesday, June 25, 2013
Dear EarthTalk: How are monarch butterflies doing today? They used to pass through my area in big numbers, but in the last few years there seem to be many fewer.
The monarch butterfly, royally adorned in black, white and reddish-orange and able to migrate as far as 2,800 miles, is a true wonder of nature. Each year monarchs travel from Canada and the U.S. to hibernate in the forests of central Mexico. But in recent years the monarchs have been in sharp population decline due to habitat loss, eradication of the plants it depends upon and other environmental factors.
The decline in monarchs has been going on for two decades, but the last few years have been particularly worrisome. Mexico's National Commission of Natural Protected Areas reports a 59 percent decline in the area of forest there occupied by overwintering monarchs since December 2011. Meanwhile, the World Wildlife Fund reports that overwintering populations along the California coast have shrunk from over a million individuals counted at 101 sites in 1997 to less than 60,000 at just 74 sites in 2009. The International Union for the Conservation of Nature, which maintains the "Red List" of endangered species around the world, recognizes the monarchs' annual migration as an "endangered biological phenomenon."
According to Monarch Watch, an educational outreach program based at the University of Kansas that engages citizen-scientists in monarch monitoring and conservation efforts, habitat destruction is one key driver in the monarch's demise: "New roads, housing developments and agricultural expansion ... all transform a natural landscape in ways that make it impossible for monarchs to live there." Also, drought and record-high temperatures in North America in 2012 triggered an earlier-than-usual monarch migration. This disrupted the butterflies' breeding cycle by drying out their eggs prematurely.
The hot weather has also reduced the nectar content of the milkweed plants that monarch larvae depend on. In addition, milkweed is becoming scarce due to farmers' increasing reliance on herbicides. Most of the soy and corn crops grown in the U.S. are genetically engineered to resist herbicides. This means even more chemical spraying -- and far fewer milkweed plants. Nectar-producing plants that attract adult butterflies are facing a similar fate, further complicating survival for the monarch.
It won't be easy to stem the tide of human development that threatens the species' long-term survival. In 2008 the Commission for Environmental Cooperation, set up under the North American Free Trade Agreement to help the U.S., Canada and Mexico coordinate on environmental initiatives, published its North American Monarch Conservation Plan to establish a conservation blueprint for the butterflies. Key aspects of the plan include the creation of incentives for the conservation of overwintering sites and the restoration of breeding habitat throughout the butterfly's extensive range.
In the meantime, the Mexican government has worked with WWF and other groups and made strides in restricting logging in areas critical to monarch populations. And in the U.S., monarch habitat restoration work in California and other parts of the U.S. have helped provide the butterflies some relief. Whether these and other efforts are enough to rescue the monarchs remains to be seen.