Technology‎ > ‎

Mexico Monarch Migration Sees Lowest Numbers In Twenty Years

posted 21 Mar 2013, 15:08 by Mpelembe   [ updated 21 Mar 2013, 15:09 ]

Conservationists say monarch butterfly colonies in Mexico have diminished to their lowest levels in twenty years. For centuries, the butterflies have spent the northern winter in Mexico before flying back to the United States and Canada in the spring but this year, following a trend that began in the 1990s, there were nearly 60% fewer than twelve months ago.

EL ROSARIO, MICHOACAN (MARCH 20, 2013) (REUTERS) -  By the end of March, the monarch migration north from Mexico to the US and Canada is underway so only the stragglers can be seen. This year however, conservation groups say there weren't that many butterflies to begin with.

They say monarch butterfly colonies in Mexico reached their lowest numbers in 20 years. They say the count is indicative of a serious problem and that the iconic insect is under threat.

Millions of butterflies make a journey each year from north America to winter incentral Mexico's warmer weather but the size of that migration can vary wildly.

This winter, fewer of the orange and black insects arrived in Mexico than ever before, researchers say, with the nine butterfly colonies occupying a total area of 2.94 acres (1.19 hectares) of forest - representing a 59 percent decrease from the 2011-2012 survey of 7.14 acres (2.89 hectares).

Researchers estimate the size of the butterfly colonies based on the area they occupy in a forest through conducting bi-weekly tours.

"We followed a monitoring process to measure the area they occupy in a forest. You find clusters of butterflies in the whole region. What we obtained during this season was an area of 1.19 hectares, which is quite a low number in relation to the 20 years we have been carrying out surveys, which represents 59 percent less of what we had last year," said the director of the Monarch Butterfly Biosphere Reserve, Gloria Tavera.

According to researchers who started census-taking in 1993, the latest drop is likely due to a decrease in the milkweed plant (Asclepias) - a primary food for monarchs - from herbicide use in the butterfly's reproductive and feeding grounds in the US, as well as extreme climate fluctuations during the winter and summer seasons affecting butterfly reproduction.

Nevertheless, in 2011 monarch butterfly colonies in Mexico more than doubled in size after bad storms devastated their numbers in 2010.

Illegal loggers have picked away roughly three percent of a 138,000 acre reserve since it was created in 2000 but officials say they now have that illicit harvest under control. Yet small scale logging continues and poses a threat. The World Wildlife Fund (WWF) also points to an expansion of farming corn for ethanol in the US as a reason for the butterfly's reduced numbers. It says large-scale farming is crowding out the milkweed that the butterflies dine on during their cross-continental flight.

"Illegal logging is a situation which has largely been controlled but small scale illegal logging continues which is also an important threat for the monarch butterfly. From the point of view of habitat in the United States and Canada, several conservation groups are planting milkweed plant in order to restore this in areas visited by the monarch butterfly but definitely the US government has to do much more to limit and restrict the use of herbicides which are affecting monarch butterflies through lack of milkweed plant," said Omar Vidal, director of the Mexicobranch of the WWF.

A guide at the reserve in El Rosario Michoacan, Daniel Garcia, who helped conduct the survey, says he has seen a drop in butterfly numbers.

"I used to help to carry out the count in three or four different butterfly clusters and now we only counted in one area, that is why the butterfly count was lower this year."

The survey, led by World Wildlife Fund (WWF) and Mexico's National Commission of Protected Areas (CONAP) during the 2012-2013 winter season, was conducted in five hibernation colonies inside the Monarch Butterfly Biosphere Reserve, with two in the State of Mexico and three in Michoacan as well as four colonies outside the reserve with three in the State of Mexico and one in Michoacan.