All-Time Low Monarch Butterfly Migration to Mexico

‘GMO, Herbicide-Tolerant Crops’ identified as one of likely causes of butterfly declines.

Activist Post

Monarch butterfly experts including the University of Minnesota’s Karen Oberhauser are calling on leaders in Canada, the United States and Mexico to agree on a plan to take immediate action to conserve monarch migration. The leaders will gather at the North American Leaders’ Summit Feb. 19 in Mexico.

The urgent plea came today (Wednesday, Jan. 29) during a press conference in Mexico announcing that the number of monarch butterflies hibernating in Mexico reached an all-time low in 2013.

“Mexico, the United States and Canada must undertake cooperative conservation efforts to ensure that sufficient high quality habitat is available on the monarchs’ wintering grounds and sufficient breeding and migration habitat is available in all three countries to maintain, and ideally enhance, North American monarch populations,” Oberhauser said.

Surveys of forested area used by hibernating monarchs in Mexico showed that just .67 hectares of forest were inhabited by monarchs during December 2013, a 44 percent drop from the same time the previous year, according to data collected by the WWF-Telcel Alliance and Mexico’s National Commission for Protected Areas. The findings represent the smallest area since surveys began in 1993.

Forest area inhabited by monarchs in Mexico is used as an indirect indicator of the number of butterflies arriving from Canada and the United States each year following a migration of more than 4,000 kilometers. The butterflies spend November through March hibernating in Mexico’s temperate forests.

The vast majority of monarchs in the Mexican wintering sites grew up on milkweed plants in the United States and Canada, and migrated through vast stretches of these countries to reach their winter home. Several lines of evidence show that the Upper Midwestern U.S. is the current major source of the monarchs overwintering in Mexico, Oberhauser said.

Many factors have contributed to a sharp decline in monarch populations in recent years, including loss of reproductive habitat caused by land-use changes and reduction of milkweed (primary food source for monarch larvae) from herbicide use in the United States and Canada; extreme climate conditions in Canada, the United States and Mexico; and deforestation and forest degradation in overwintering sites in Mexico.

“Tragically, much of their breeding habitat in this region has been lost to changing agricultural practices, primarily the exploding adoption of genetically modified, herbicide-tolerant crops in the late 20th and early 21st centuries,” Oberhauser said. “These crops allow post-emergence treatment with herbicides, and have resulted in the extermination of milkweed from agricultural habitats.”

Additional habitat has been lost due to suburbanization of agricultural land, she said.

“Habitat protection in monarch wintering sites alone cannot protect the spectacular North American monarch migration from intensifying human pressures,” Oberhauser said.

Considering the challenges faced by the monarch butterfly and the clear evidence that their populations are declining, Oberhauser said it is vital to mobilize as many people as possible in conservation work, and that efforts are carefully planned to help the butterfly recover.

“Through our collective efforts, monarch populations can rebound, so that their migrations may be appreciated by many generations to come,” Oberhauser said.

While monarchs don’t play a key role in any ecosystem and their removal from specific ecosystems would probably not have lasting repercussions, Oberhauser said monarchs deserve protection for both ethical and more selfish reasons.

“Ethically, preserving monarchs is the “right” thing to do,” she said.

From a selfish perspective, Oberhauser said, people can learn a great deal about migration, species interactions, insect population dynamics, and insect reproduction by studying monarchs.

“Monarchs have a great deal to teach us about how the natural world works, and I would argue that understanding the natural world will benefit us,” Oberhauser said.

Source: University of Minnesota

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