Maine Sea Grant College Program
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Over the past two decades, researchers have observed declines in populations of both monarch butterflies (over 70% in some areas) and milkweed. Climate-related factors contributing to these declines include increasing frequency of intense winter storms and near freezing temperatures in monarch overwintering areas in Mexico, and severe droughts in the southwestern and southeastern United States, which affect both species. If these trends continue, they could create a mismatch in time or space between monarch breeding cycles along their northward migration (April to August) and the growth and survival of milkweed plants eaten by monarch caterpillars.
Bisson, Beth and Stancioff, Esperanza, "Signs of the Seasons Program Species in Focus: Monarchs and Milkweed, an Ecological Relationship Threatened by Climate Change" (2013). Maine Sea Grant Publications. 84.
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