For all fans of monarch butterflies, a new article in American Entomologist may be of interest. Lincoln Brower and colleagues describe the most devastating weather event for the monarchs since studies began 24 years ago.
For many years it was known that monarch butterflies migrated; but not until 1975 did scientists discover that most monarchs in the eastern half of the United States migrate to a remote mountainous site in south-central Mexico. The Monarch Butterfly Biosphere Reserve was designated a World Heritage Site in 2008, and is located in a pine-oak forest ecoregion on the border of Michoacán and State of Mexico, about 60 miles northwest of Mexico City.
The actual size of the preserve used by monarchs grows and shrinks each year depending on the numbers of returning monarchs and weather conditions at the site. Since the early 1990’s when records began, the size of the overwintering site has fluctuated from a high of 44 acres in 1996-97 to a low of 1.6 acres in 2013-14. Computer models have predicted that, due to concerns about effects of illegal logging in the preserve, weather extremes possibly due to climate change, and the large fluctuations in the modern population of overwintering monarchs, the chance that the eastern monarch migration will cease and the butterflies become functionally extinct over the next 20 years is between 11 and 57%.
Just when scientists hoped the monarch preserve was making a comeback a 2016 storm blew down trees in the reserve and reached lethal low temperatures, killing many butterflies. Brower’s article and its accompanying pictures tells the story. The authors note with alarm that government permission given to private companies to log fallen trees in the preserve following the storm has caused serious thinning of the protective tree canopy. They estimate that between 30 and 38% of all overwintering monarch butterflies were killed during the 2016 storm. Of even more concern, however, is that the long-term health and viability of the Monarch Butterfly Biosphere Reserve may be compromised.
It’s monarch season right now in Texas, so don’t miss your best opportunity to get outdoors to catch our Texas state insect as it slips south to Mexico. The story of the monarch plight reminds us not to take our noble black-and-orange butterfly for granted. If we do, the fall monarch migration may be a sight that our next generation will no longer remember.