Winter monarch butterfly population up 144 percent

Scientists say the number of monarch butterflies is at its highest point in over a decade.

PJ Liesch, Extension entomologist, University of Wisconsin-Madison, Division of Extension and the College of Agricultural and Life Sciences, said scientists assessed the eastern monarch population in the winged insects' wintering grounds in Mexico.

"Scientists don’t go out and count individual butterflies, there’s just too many of them," Liesch told Lorre Kolb in a recent interview. "What they do though is the monarchs pack down densely and they hang off of these conifer trees in a mountainous area in Mexico and so scientists can estimate the area, the acreage and that’s how they get a winter assessment of how healthy the monarch population is." 

Scientists estimate that the population is up 144% from last winter, the highest jump in over a decade.

While that's good news, Liesch says a lot can happen to the butterflies between Mexico and the U.S. during the fall and spring migration. 

"(Last summer), we seemed to have a bumper crop of monarchs. And it was great news, but it’s always hard to take these observations and reports and know does that actually mean we have higher monarch butterfly populations," he said. "Those butterflies faced a perilous 2000 mile journey to their overwintering grounds in Mexico and a lot of bad things could have happened on the way so they wouldn’t have made it. But they seem to have made it."

While the wintering monarch population seems to be thriving, Liesch says in order to return to their summer grounds, the butterflies can still face some tough situations.

"If they get clobbered with winter storms, with freezing rain, that can be hard on them, ' he said.

Liesch said the plight and well-being of the iconic butterfly is of special interest to scientists, as the monarchs often serve as an indicator for other species.

"We’ve been experiencing monarch declines for some time and there’s concerns there, but for every monarch there’s probably other species also facing similar declines and they simply don’t get the attention, so we can use it as an indicator for some of these other pollinator species that are out there,' Liesch said.

While the western monarch population out on the West Coast is spared the arduous journey to Mexico, migrating instead to southern California, Liesch said the overwintering counts show the population is at "perilously low numbers".

The loss of habitat and decreasing number of flowering plants have created a shortage of food for the migrating insects.

"There are also some diseases that can impact monarchs as well, and so all of these different factors may be at play with monarch declines," he said.