Dwindling Monarchs

ElRosario_aerialIn December we visited the wintering spot for monarch butterflies.Last week, I blogged about the butterflies we saw. It was impressive but apparently there should have been many more butterflies than we saw according to an article in the NYT yesterday about the dwindling number of the butterflies over the last five years.

The aerial picture here gives you an idea of the number of butterflies in one spot in Mexico, the orange-colored trees look that way because there are so many orange monarch butterflies clinging to each tree!

Below is a shortened excerpt of the NYT article:

Mexico is the southern terminus of an age-old migration widely called one of the world’s great natural spectacles in which monarch butterflies shuttle back and forth between  summertime havens in Canada and a single winter home in Mexico’s Sierra Madre mountains,. It is now in danger of effectively vanishing.

An internal compass guides the butterflies each fall to a small cluster of mountains where ideal temperatures and humidity allow them to rest, clinging to trees by the millions like brilliant orange capes. Then in March they set out on the 2,500-mile-plus trip north, breeding and dying along the way. It’s their descendants that actually complete the migration.

At their peak in 1996, the monarchs occupied nearly 45 acres of forest. …the span of forest inhabited by the overwintering monarchs shrank last month to less than two acres. Not only was that a record low, but it was just 56 percent of last year’s total, which was itself a record low. This is the third straight year of steep declines…

Over time, the number of butterflies has varied from year to year, sometimes wildly, but the decrease in the size of the migration in the last decade has been steep and generally steady.

The latest drop is best explained by a two-year stretch of bad weather. But the loss of habitat is a far more daunting problem. Monarchs lay their eggs only on milkweed which has rapidly disappeared from the Great Plains over the last decade.

As corn prices have risen, farmers have planted tens of millions of acres of idle land along the monarchs’ path and increased use of herbicides on fields of herbicide resistant corn all but wiping out milkweed that once sprouted between rows of corn and soybean.

Now the monarchs must travel farther and use more energy to find places to lay their eggs. With their body fat depleted, the butterflies lay fewer eggs, or die before they have a chance to reproduce.

The monarchs are the most visible victims of the habitat loss. A wide variety of pollinators and other insects, including many beneficial to farmers, are also disappearing along with the predators that feed on them.