In an article on the news site of the journal Science on varying studies related to monarch butterfly migration declines, Ernest Williams, the William R. Kenan Professor of Biology Emeritus and lecturer in biology, warned that concerns over migration “should be added to—but not replace—the other issues we know to be affecting monarchs.” The Aug. 5 article was titled “Monarch butterfly studies tell a perplexing tale.”
Over the past 20 years, the number of monarchs returning to the largest known wintering ground in central Mexico’s highland forests has plunged by more than 90% (Science, Feb. 7, 2014), according to the publication. Many have blamed the decline primarily on the expansion of herbicide-resistant crops in the summer breeding grounds, which has led to the wide use of chemicals that kill milkweed. But few studies have systematically examined monarch population trends in these areas.
The journal Science is a publication of the American Association for the Advancement of Science.