Annual Movement Of Monarch Butterflies
The annual movement of monarch butterflies (Danaus plexippus) is among nature’s most stunning sights.
Millions of the butterflies move yearly from the as far north as Nova Scotia all the way to wintering premises in the woodlands of Mexico, a journey of around 3,000 miles (4,800 kilometers) that takes four generations.
The lifespan of the monarch butterflies is short and they need to produce four generations of offspring to complete the entire trip. The first three generation live just a couple of weeks, but the fourth generation lives several months in order to complete their journey.
Annually less and less monarch butterflies make the trip, because monarch populations have been decreasing throughout The United States and Canada for over 15 years.
To estimate population size, researchers determined monarch numbers while they were assembled at their wintering grounds in the woodlands of Mexico.
On average the monarch butterfly coverage from 1994-2014 covered 6.39 hectares. The monarch coverage during the 2013-2014 winter was only 0.67 hectares in Mexico’s woodlands, which was a drop of 44 percent from 2012.
The decrease in monarch butterfly numbers has been primarily blamed on the loss of milkweed, the plants on which monarch caterpillars naturally feed.
Karen Oberhauser, a monarch biologist from the University of Minnesota and co-author of the research study stated breeding, migrating and overwintering environment loss are also aspects impacting monarch populations.
The increase in genetically-modified, herbicide-tolerant plants, such as corn and also soybeans, and the spread of the herbicides used to protect the crop has caused a severe decrease in milkweed, and therefore a loss of reproducing habitat.
