When it comes to monarchs, fall migration matters

New research shows that a critical piece of the butterfly's annual cycle was missing -- the fall migration.Scientists studying monarch butterflies have traditionally focused on two sources for their decline -- winter habitat loss in Mexico and fewer milkweed plants in the Midwest.New research conducted by Michigan State University and published in Proceedings of the National Academy of Sciences, however, shows that a critical piece of the butterfly's annual cycle was missing -- the fall migration. By focusing on this southerly trek, as well as changing the scale at which winter populations are examined, scientists reveal a wider, more-accurate spectrum of threats that have contributed to the monarch population's downward trend.