Threats include habitat loss - particularly the loss of milkweed, the monarch caterpillar's sole food source - and mortality resulting from pesticide use.
Endangered Species Act protection may be warranted for Monarch butterflies, according to the US Fish and Wildlife Service.
The agency will now conduct a one-year status review on monarchs, which have declined by 90% in the past 20 years.
The migratory butterflies are especially vulnerable as they migrate vast distances of 3,000 miles or more each year, between the US, Mexico and Canada. The migration cycle is unique in the natural world as it spans multiple generations.
"This journey has become more perilous for many monarchs because of threats along their migratory paths and on their breeding and wintering grounds", says the FWS.
"Threats include habitat loss - particularly the loss of milkweed, the monarch caterpillar's sole food source - and mortality resulting from pesticide use. Monarch populations have declined significantly in recent years."
This important first move towards ESA protection comes in response to a petition by the Center for Biological Diversity, Center for Food Safety, Xerces Society and renowned monarch scientist Dr. Lincoln Brower,
"Our petition is a scientific and legal blueprint for creating the protection that the monarch so direly needs, and we are gratified that the agency has now taken this vital first step in a timely fashion", said George Kimbrell, Senior Attorney for Center for Food Safety.
Path to extinction propelled by GMO crops
The butterfly's dramatic decline is being driven in large part by the widespread planting of genetically engineered crops in the Midwest, where most monarchs are born.
The vast majority of genetically engineered crops are made to be resistant to Monsanto's Roundup herbicide, a potent killer of milkweed, the monarch caterpillar's only food. The dramatic surge in Roundup use with Roundup Ready crops has virtually wiped out milkweed plants in Midwestern corn and soybean fields.
In the past 20 years it is estimated that these once-common iconic orange and black butterflies may have lost more than 165 million acres of habitat - an area about the size of Texas - including nearly a third of their summer breeding grounds.
Sarina Jepsen, the Xerces Society's endangered species director, said: "Protection as a threatened species will enable extensive monarch habitat recovery on both public and private lands."
Tierra Curry, a senior scientist at the Center for Biological Diversity, added: "The Endangered Species Act is the most powerful tool available to save North America's monarchs, so I'm really happy that these amazing butterflies are a step closer to the protection they so desperately need."
The population has declined from a recorded high of approximately 1 billion butterflies in the mid-1990s to only 35 million butterflies last winter, the lowest number ever recorded. The overall population shows a steep and statistically significant decline of 90% over 20 years.
Threats include habitat loss - particularly the loss of milkweed, the monarch caterpillar's sole food source - and mortality resulting from pesticide use.
In addition to herbicide use with genetically engineered crops, monarchs are also threatened by global climate change, drought and heat waves, other pesticides, urban sprawl and logging on their Mexican wintering grounds.
Scientists have predicted that the monarch's entire winter range in Mexico and large parts of its summer range in the states could become unsuitable due to changing temperatures and increased risk of drought, heat waves and severe storms.
The butterflies are highly vulnerable to extreme weather events: a single winter storm in 2002 killed an estimated 500 million monarchs - 14 times the size of the entire current population.
Monarch population up this year - but still highly vulnerable
Found throughout the United States during the summer months, in winter most monarchs from east of the Rockies converge in the mountains of central Mexico, where they form tight clusters on just a few acres of trees. Most monarchs west of the Rockies migrate to trees along the California coast to overwinter.
The size of the overwintering population in Mexico is expected to be up this year due to favorable spring and summer weather, but even with the expected one-year population increase, the monarch population will only be a fraction of its historical size.
Monarchs need a very large population size to be resilient to threats from severe weather events and predation. Nearly half of the overwintering population in Mexico can be eaten by bird and mammal predators in any single winter.
The FWS is currently seeking scientific and commercial data and other information through a 90-day public information period, including:
- The subspecies' biology, range and population trends, habitat requirements, genetics and taxonomy;
- Historical and current range, including distribution patterns;
- Historical and current population levels and current and projected trends;
- The life history or behavior of the monarch butterfly that has not yet been documented;
- Thermo-tolerance range and microclimate requirements of the monarch butterfly;
- Past and ongoing conservation measures for the subspecies, its habitat or both; and,
- Factors that are the basis for making a listing determination under section 4(a) of the ESA.
Next the Service will either issue a '12-month finding' on the monarch petition that will propose protection under the Endangered Species Act, reject protection under the Act or add the butterfly to the candidate waiting list for protection.
