Monarch Butterfly Threatened By Decline In Habitat And Nectar

Monarch butterflies are threatened by a lack of milkweed, as well as the widespread herbicides and genetically modified crops that contribute to sparse autumnal nectar sources. Other threats include the break-up of weather and habitats.

In any year, four generations of monarch butterflies travel all over North America through 2,000 miles, starting in early spring after they leave their wintering grounds in Mexico. Initially, millions of monarchs travel through Texas and Oklahoma, while the subsequent generations fly into the Midwest and Northeast. With autumn, the fourth generation comes back to Mexico for the subsequent winter.

Two years ago, the monarch butterfly population plummeted to an all-time low, but today, the population is six times the population at that time, mainly due to improved weather and escape from the severe drought in Texas.

Still, the species faces threat.

"Thanks to years of data collected by the World Wildlife Fund and citizen-scientists across north America, we have pieced together the monarch life cycle to make inferences about what is impacting the butterflies," said Anurag Agrawal, professor of ecology and evolutionary biology at Cornell University and senior author of the study.

Without enough nectar to feed on while travelling long distances, as well as habitat loss and insecticides, the traveling monarch butterflies continue to decline.

"Given the intense interest in monarch conservation, the blame being put on herbicide use and the national dialog about potentially listing monarchs under the endangered species act, we have to get the science right," Agrawal said.

The findings were recently published in the journal Oikos.