Release of Results of Wintering Monarch Census - March 21, 2023

[donald...@gmail.com]

Thanks to my colleague, Dr. Karen Oberhauser, for sharing this commentary. This news has now been widely distributed around the world:

"On March 21, 2023, the World Wildlife Fund-Telmex Telcel Foundation Alliance (WWF) and the National Commission of Protected Natural Areas in Mexico (CONANP), released data from the winter 2022–23 monarch butterfly population counts. At the wintering sites in central Mexico, monarch population size is compared from year to year by the number of hectares (one hectare = 2.5 acres) occupied by trees containing monarchs. WWF and CONANP have been monitoring this area since 2004, with similar data from 1993-2003 collected by the Monarch Butterfly Biosphere Reserve (MBBR). While the number of monarchs in a hectare varies from year to year and is difficult to estimate, our best estimate is that the average is about 21 million.

In December 2022, monarchs occupied 2.21 hectares, compared to 2.84 hectares at the same time in 2021, or a 22 percent decrease. The average for the past decade is 2.75 hectares, and the population has been declining since we began measuring it (see graph).

A 2021 analysis* shows that the most important factor affecting for winter numbers is summer population size. Summer population size is driven by several factors, but the important is weather in the southern United States in the spring--when monarchs are migrating north from wintering in Mexico. Summer weather, overall herbicide use in crop fields, and late winter population size are also contributing factors. Hotter, drier, colder, or wetter conditions in the southern U.S. when monarchs are moving through are bad. Last spring was very dry – see the drought monitor map from a year ago. One effect of climate change is more extreme weather variability, which may pose additional challenges to monarchs.

The best way to support monarchs is to raise the ceiling by creating more habitat. That means an all-hands-on-deck approach: restoring habitat in our yards, places of work, schools, and churches; along roadsides, utility rights-of-ways, and railroads; and in areas currently used for crops that aren’t very productive. This work supports monarchs and the thousands of other species in the same habitats.

We also need to work to mitigate climate change. The report this week from the Intergovernmental Panel on Climate Change needs to be a call to action; we know that the conditions predicted by climate models will be bad for monarchs, but they’ll also be bad for us and most other organisms on earth."

Eduardo Rendon, Subdirector of Terrestrial Ecosystem Programs, WWF Mexico, has sent me a copy of the report released yesterday. Please write to me privately should you wish to read a copy.

Further, this coming Saturday, the Toronto Entomologists' Association will be hosting the annual student research symposium by Zoom. I make note of this particular presentation being made: Campbell Allan McKay. Jeremy McNeil lab, Western University - Could the use of different species of milkweed as larval hostplants influence the fall migration of Monarchs?

: