In DepthConservation Biology

Monarchs pose a puzzle

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Science  07 Aug 2015:
Vol. 349, Issue 6248, pp. 570-571
DOI: 10.1126/science.349.6248.570

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Summary

Eastern North American monarch butterflies have seen a dramatic decline on their major wintering grounds in central Mexico's highland forests. But few studies have systematically examined monarch population trends in other areas and at other points in the insects' life history. Now, a collection of seven monarch studies published this week in the Annals of the Entomological Society of America aims to do just that. The picture that emerges, however, is puzzling to researchers. One paper suggests that, even as wintering populations of monarchs have plummeted over the past 2 decades, there's been no similarly steep decline in a key summer breeding area that stretches across the midwestern United States and southern Canada. Others find that some early fall migration counts also show no major downward trend. At the same time, however, the butterflies may be laying fewer eggs overall, another study concludes. In all, the papers are raising questions about how well researchers understand the mechanisms behind the charismatic black-and-orange insects' overwintering decline, some researchers say. They point to losses the butterflies might sustain during the fall migration in addition to the loss of milkweed breeding habitat due to the spread of herbicide-resistant crops as potential drivers of decline.

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