One of nature’s most beautiful sights is when a monarch butterfly comes fluttering into view.

Monarchs are the only known North American butterfly to migrate south for the winter, hibernating and returning in the spring as birds do. However, a new report finds the number of these butterflies hibernating in Mexico reached an all-time low in 2013, possibly due to loss of habitat, climate change and the use of insecticides.

“The combination of these threats has led to a dramatic decline in the number of monarch butterflies arriving to Mexico to hibernate over the past decade,” said Omar Vidal, World Wildlife Fund-Mexico director general. “Twenty years after the signing of NAFTA, the monarch butterfly migration – a symbol of cooperation between our three countries – is in grave danger.”

Depending on just how far north they make their summer homes, the butterflies’ journey south can be a long as nearly 5,000 kilometers.

Monarch butterflies that summer in eastern North America spend the winter in Mexico, while those living in the west winter in California.

The report, released last week by the World Wildlife Fund, Telcel Alliance and Mexico’s National Commission for Protected Areas (CONANP), surveyed Mexican forest areas known to be used by hibernating monarchs. Researchers found that only 6,677 square meters of forest area were populated by monarchs during December 2013. This finding shows a 44-percent drop from the same time in 2012, and represents the smallest area occupied by the monarchs since 1993, when these annual surveys began.

(c) WWF

(c) WWF

The annual survey is used by researchers as a way to indirectly tally the number of butterflies that make the trip from the United States and Canada during the yearly migration.

Using spatial analysis software, researchers toured 11 butterfly sanctuaries, that have historically been known to have a presence of monarch colonies, once every other week in order to determine the specific location of the butterflies and how much of the forest land they inhabited during their winter hiatus.

Scientists have cited numerous factors that may have caused the dramatic drop in the number of monarchs in recent years.

According to the report, some of the reasons for the population drop include:

•  A loss of the monarch’s reproductive habitat, which may have been caused by changes in land use

•  A decrease in the monarch larvae’s primary food source – milkweed – due to the use of herbicide

•  Extreme climate conditions in Canada, the United States and Mexico

•  A loss of forest area (deforestation) as well as and forest degradation throughout the areas of Mexico known for hosting monarchs in the winter

Monarch butterflies, gather in forrested areas of Mexico each winter (Raina Kumra via Flickr/Creative Commons)

Monarch butterflies gather in forested areas of Mexico each winter. (Raina Kumra via Flickr/Creative Commons)

Officials from Canada, Mexico and the United States will meet Feb. 19 in Toluca, Mexico, for the North American Leaders’ Summit.  The WWF is calling on participants to agree on a plan that calls for immediate action to conserve the monarch migration.

“Considering the challenges faced by the monarch butterfly and the clear evidence that their populations are declining, it is vital to mobilize as many people as possible, and that our efforts are carefully planned to help this butterfly recover, so their wonderful migration can be appreciated for many more generations”, said Karen Oberhauser a professor at the University of Minnesota who has been studying Monarchs since 1984.