Monarch Butterfly Wings Reveal Clues to Their Birthplaces

Scientists may have found a bit more about California's overwintering monarch butterflies. They've discovered that their wing patterns may actually yield clues to their birthplaces.

The monarch butterfly of North America overwinters along the California coast and in the central mountains of Mexico. Previous studies have indicated that the western monarchs---those that originate west of the Rocky Mountains-overwinter along the California coast, while the monarchs that develop east of the Rockies overwinter in central Mexico.

In this latest study, the researchers looked at the wester monarch population in depth. They collected butterflies from the trees where they had gathered in four California overwintering sites in early December.

The researchers examined the butterflies' wings for shape, structure and telltale hydrogen isotopes. The different isotopes are actually known to be associated with precipitation in various regions in the United States and allowed the researchers to correlate the wing size and shape with how far the butterflies had migrated from their birthplace.

Of the 114 overwintering butterflies sampled, they found that 30 percent developed in California's southern coastal range, 12 percent in the northern coast and inland range, 16 percent in the central range, and 40 percent in the northern inland range. Interesting, the butterflies from different locations had marked differences.

The findings reveal a bit more about the monarch butterfly. More specifically, they show how examining monarch butterfly wings can tell scientists a bit more about their migration patterns.

The findings are published in the journal Ecography.

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