Yellowstone Times

From 2003 to 2019, Harlan Radcliff, an amateur butterfly enthusiast, dedicated his lunch breaks to observing monarch butterflies at Camp Dodge in central Iowa. His meticulous records have now enabled Montana State University ecologist Diane Debinski to analyze the effects of climate variations on the migratory patterns of these butterflies. The findings were published recently in the Journal of Animal Ecology.

Debinski, head of MSU’s Department of Ecology, led the research focusing on eastern monarchs, which winter in Mexico and spend summers east of the Rockies. This study is part of a larger investigation funded by the U.S. Department of Defense on how climate change impacts three significant butterfly species using DoD lands.

Monarch butterflies were recently considered for listing as threatened under the Endangered Species Act. The paper’s co-authors include Elizabeth Crone from UC Davis, Sonia Altizer from the University of Georgia, and Norah Warchola from Iowa State University.

The team expected environmental changes to affect key events like arrival and departure dates for Camp Dodge's monarch population. They also examined phenological changes in common milkweed plants used by monarch caterpillars.

“If one shifts and the other doesn’t,” Debinski explained, it could result in asynchrony between butterfly arrivals and milkweed growth stages. For historical data on Midwestern milkweed growth, researchers consulted herbariums in Iowa, Minnesota, and Wisconsin.

In 2020 fieldwork was conducted where monarch eggs were placed on milkweed plants at different intervals to assess potential shifts in spring arrival times affecting larvae development. Despite expectations that spring arrivals would occur earlier, it was found that while arrival timing remained unchanged by 2019 compared to 2003, fall migration was delayed by nine days—a pattern mirrored by later blooming milkweed.

Debinski noted this indicates a need to further study fall season phenology due to possible implications for population dynamics over time: “A longer season could have benefits and it could also have costs.” Potential costs might include increased exposure to predators or parasites or developmental traps where late-laid eggs fail to develop into adults or adults emerge when conditions are unsuitable for migration.

While no change was observed in arrival times during their survey period from 2003-2019 at Camp Dodge—the experiment showed mismatched hatching times can be costly with lower early-season larval survival when hatch timing shifted two weeks earlier than natural occurrences—a relevant finding for other areas if differing milkweed species undergo various phenological shifts compared with common milkweed.

Though Radcliff has since passed away his long-term data collection provided valuable insights revealing not only migration pattern changes but also declining monarch population growth consistent with trends reported by U.S Fish & Wildlife Service statistics over recent decades.

“Discussions about phenology often exclude migratory butterflies because they experience climates across multiple places,” said Debinski. “Our research showed even migratory species can show shifts in phenology; more information on these factors helps us conserve monarchs alongside many other conservation concern species.”