Monarch Butterfly Decline in North America

Article by Hank Tyler
Photos by Manu Rajan

Monarch Butter y populations in North America have declined an estimated 90% in the last two decades. Monarchs are beautiful black and orange butterflies with a wing span of 6 cm to 8 cm. This colorful iconic butter y’s springtime northward migration spans several generations. They lay their eggs on milkweed plants containing toxic alkaloid chemicals. The caterpillars that hatch, feed almost exclusively on milkweed leaves and in the process concentrate toxic alkaloids in their bodies, rendering them poisonous to predators such as birds. 
During autumn Monarchs migrate south to a tiny area less than 100 hectares in the Mexican State of Michacan about 100 km north of Mexico City. The Monarch overwintering area is located in the 56,000  hectare Mariposa Monarca Biosphere Reserve. Monarchs cluster in oyamel fir trees at around 2,700 meters elevation. Despite its designation as a World Heritage Site, illegal logging continues in this area. 

A combination of factors contribute to the Monarch’s dramatic decline. Massive conversion of native grassland habitats in the North American mid-west for commercial agriculture has destroyed much of the milkweed. Increasing use of chemical herbicides in current agricultural practices, such as no-till farming, has eliminated milkweed plants in and nearby agricultural fields. Cutting of pine and r trees in the Mexican wintering grounds has reduced the size of wintering habitat. And finally, colder than normal winter temperatures have killed many overwintering Monarchs. Monarchs are important plant pollinators. Their former abundance indicated stable and healthy ecosystems. Their rapid decline is another indication of significant changes to the earth’s ecological habitats. 

There are a number of NGOs working to protect the remaining overwintering habitat, and to encourage the restoration of milkweed by new plantings. 

See: www. monarchwatch.org. 

Volunteer citizen projects to promote Monarch Butter y conservation include counting migrating butterflies, planting milkweed plants, and protecting fields with existing milkweed plants. 
Hank Tyler is an American naturalist, who worked on conservation issues for Maine State government and also had been a very active citizen volunteer in NGOs for 40 years. 
Photographs are from India denoting the worldwide distribution of Monarchs, by Manu Raghurajan.