Crisis Looms for Monarch Butterfly Migration

Conservationists have long urged federal protection for monarch butterflies due to declining populations and habitat loss. They advocate for federal listing under the Endangered Species Act. However, a new study from the University of Georgia questions this approach, suggesting monarchs struggle mainly with their southern migration. This could impact how the US Fish and Wildlife Service (USFWS) manages species protection, with a decision expected by December 4.

Historically, scientists assessed monarch trends by counting populations in Mexico, noting a steep decline. Yet recent data shows consistent hatching rates in northern areas. Andy Davis from the University of Georgia suggests the key issue may be monarchs failing to survive migration south.

“Although the Mexico overwintering colonies have declined, summer populations in the US and Canada remain stable,” Davis noted. “The problem might be monarchs not reaching their winter destinations.”

Monarchs traditionally lay eggs in southern Canada and the northern US, migrating south to Mexico in the cold months. During migration, they form roosts, some with thousands of butterflies. Upon reaching Mexico, they overwinter for months before returning north.

Researchers reviewed 2,600 monarch roost observations from Journey North from 2006 to 2023. Recent reports show smaller roosts along migration routes. Bill Snyder, an agroecology professor and study co-author, emphasized the value of this citizen-collected data over vast areas and time periods.

Davis, Snyder, and postdoctoral researcher Jordan Croy discovered that roost sizes had decreased by 80% at the southernmost migration points. Davis explained that 20 years ago, Texas roosts had thousands of monarchs, now reduced to hundreds.

The study explored other causes, noting monarchs haven’t changed migration timing, and climate change isn’t directly responsible as the route is now warmer and greener. However, climate change might indirectly affect non-native milkweed growth and extreme weather.

Jaap de Roode from Emory University, unaffiliated with the study, suggested monarchs could be roosting elsewhere, though the study addressed this possibility. “We see reported roosts but don’t know all locations,” de Roode said.

While the study doesn’t clarify why monarchs struggle with migration, it proposes hypotheses like increased parasitic diseases and the impact of non-native milkweeds and captive-reared monarchs. Davis criticized advice encouraging people to rear monarchs, which may harm them. Organizations like Monarch Watch, Monarch Joint Venture, and the Xerces Society can guide planting native milkweed.

Davis argues against listing monarchs as endangered, stating it’s based more on emotion than evidence. He warns that it could lead to counterproductive conservation efforts. “Listing them could lead to misguided help that harms monarchs,” he said.

Some researchers argue the Endangered Species Act might not effectively protect monarchs, as it wouldn’t stop non-native milkweed planting. “The focus should be on migration, which the ESA might overlook,” said Croy.

This contrasts with conservation groups like the Center for Biological Diversity, which advocates for listing monarchs as endangered. In May, 22 groups requested $100 million for monarch conservation, citing habitat loss and climate change.

Davis doubts USFWS will list monarchs as endangered due to potential legal complexities. He suggests a rule to prevent human interference with monarchs. De Roode recommends focusing on habitat protection to benefit monarchs and other species. “Creating pollinator gardens and nectar sources aids monarchs and other native species,” he said.