A new study by UC-Davis illuminates the natal origins of monarch butterflies overwintering in California. The study by Louie Yang (Dept. Entomology at UC-Davis) used stable hydrogen isotope analysis to test tissue samples from 114 butterflies at 4 overwintering locations. The study found overwintering clusters contain butterflies from California as well as interior Western states such as Idaho, Montana, Wyoming, eastern Oregon & Washington.
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