Wing Pattern Sheds Light On Birthplace Of Migrating Monarch Butterflies

A new study from the University of California, Davis, sheds light on the state's winter guests, monarch butterflies. It turns out a butterfly's wing patterns may actually yield clues to their birthplaces, researchers say.

"We hope that this paper improves our understanding of where monarch butterflies grow up in western North America," Louie Yang, lead researcher and a community ecologist in the UC-Davis Department of Entomology and Nematology, said in a news release.

The monarch butterfly (Danaus plexippus) of North America typically winters along the California coast or in the central mountains of Mexico. For their latest study, researchers examined the natal origins, or "birthplaces," of 114 butterflies collected from trees in four California overwintering sites in early December.

The four sites included: Two northern sites -- Lighthouse Field State Beach and Moran Lake, both in Santa Cruz County -- and two southern overwintering sites -- Pismo State Beach in San Luis Obispo County and the Coronado Butterfly Preserve in Santa Barbara County.

Previous research on the migration of North American monarchs indicates western monarchs -- those that originate west of the Rocky Mountains -- travel to the California coast, while monarchs that develop east of the Rockies wait out the cold in central Mexico.

The butterflies' wings were examined for shape, structure, and telltale hydrogen isotopes -- which are generally an indication of different precipitation levels. Researchers were therefore able to correlate individuals' wing size and shape with how far they migrated from their birthplaces.

Their analysis revealed 30 percent developed in California's southern coastal range, 12 percent originated in the northern coast and inland range, 16 percent in the central range, and 40 percent in the northern inland range.

"Building a clearer understanding of where they come from could help us better understand many aspects of their ecology," Yang added in the university's release.

Their study was recently published in the journal Ecography.

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