An interesting scientific paper suggests that Monarch butterflies are not arriving earlier in the United States but are staying longer in late summer before heading back to Mexico.
If you’ve been wondering about how the Monarch’s migrations have been affected by climate change, you’ll like the paper. The lead author is Diane M. Debinski, an ecologist at Montana State University.
But the heart of the paper is a set of data compiled by Harlan Ratcliff, who was an environmental engineer at Camp Dodge, headquarters for the Iowa National Guard. He compiled the data as an amateur on his lunch hour, using a technique called a Pollard walk. The technique was devised with amateur naturalists in mind.
The basic idea is to imagine that you, the observer, are in a 5-meter cube or box. You walk along a set course — the technical term is a transect — repeatedly on a schedule and record the species of interest you see in your box. Ratcliff’s findings were remarkable because they run from 2003 to 2019. The data suggests that Monarchs were staying nine days longer. The warmer temperatures in autumn extended the season for milkweed.
Sadly, Ratcliff died in 2022. But his blog, The Roused Bear, is online. If you want to get an idea of what a naturalist is like, it’s a good place to start.
• Sources: Diane M. Debinski, Norah Warchola, Sonia Altizer, Elizabeth E. Crone, “Implications of summer breeding phenology on demography of monarch butterflies”; Journal of Animal Ecology, 17 Feb. 2025, https://doi.org/10.1111/1365-2656.70004
It’s here:
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2656.70004
Harlan Ratcliff’s blog The Roused Bear is here:
https://therousedbear.wordpress.com/
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