Habitat Loss in Breeding Grounds Led to Decline of Monarch Butterflies

The alarming decline in the migratory monarchs is due to habitat loss in their breeding grounds in the U.S., a new study reveals.

Several studies have highlighted that the future of monarch butterflies is not bright as their number is dropping at an alarming rate across Mexico, California and other areas of the United States.  Much of this decline is linked to loss of milkweed - the native plants on which monarch caterpillars feed.

Providing more insight on the decline of the monarchs, researchers at the University of Guelph observed that habitat loss of the breeding grounds in the United States, not the wintering grounds in Mexico, is the main reason for the recent population decline of migratory monarch butterflies in eastern North America.

"Our work provides the first evidence that monarch butterfly numbers in eastern North America are most sensitive to changes in the availability of milkweed on breeding grounds, particularly in the Corn Belt region of the United States," said Ryan Norris, a professor in Guelph's Department of Integrative Biology.

Norris in collaboration with lead author Tyler Flockhart conducted the study that knocks down the previous belief that monarch butterflies are affected  by the disturbances on wintering grounds in Mexico, rather than a in their breeding grounds.

During the winter months a large number of monarch butterflies assemble in a small region in Mexico. It was assumed that certain factors in these wintering grounds such as climate change or deforestation were the greatest threat to the Monarch population. Efforts were made to protect their  overwintering habitat.

"The protection of overwintering habitat has no doubt gone a long way towards conserving monarchs that breed throughout eastern North America. However, our results provide evidence that there is now another imminent threat," said Flockhart.

Milkweed is the only group of plants that monarch caterpillars feed upon before they develop into butterflies. Alteration in milkweed abundance has a devastating impact. In this study the researchers created a model to predict effects of habitat loss on breeding as well wintering ground and the effect of climate change.

The main task of the researchers was to explain the decline in monarch population and also predict the future of these majestic butterfly. The results linked an increase in genetically modified herbicide resistant crops and the present decline in monarch population in eastern North America.

"Reducing the negative effects of milkweed loss in the breeding grounds should be the top conservation priority to slow or halt future population declines of the monarch in North America," Flockhart said.

The population would benefit from plantation of more milkweed in south and central United States.

The finding is documented in the journal of Animal Ecology.