2022 Monarch Butterfly Update

Guest Essay by Kip Hansen – 8 June 2022

This last March, I reported on these digital pages the marvelous and mysterious news that the census of the Western Monarch annual migration in California had shown an increase in overwintering monarchs by 100 times over the previous year.  The expert consensus had been that the Western migration would be shown to be extinct. 

But Nature does not always listen to the experts and just does what it does. 

“The butterflies hit a devastating record low last year [2020-2021], numbering fewer than 2,000 across California.” ….  “We were pretty concerned last year that we were potentially facing a reality where there would no longer be monarch butterflies in the Western US,” Sarina Jepsen, director of the endangered species program at the Xerces Society” [ source ]

That statement from Sarina Jepsen is probably a misquote – no one thinks that the Monarch Butterfly (Danaus plexippus) is going extinct in the Western U.S..  The fear is that the natural phenomena called the Western Monarch Migration will cease.  “…in 1983, the IUCN took the unprecedented step of creating a new category in the Invertebrate Red Data Book, in order to list the monarch migration as a Threatened Phenomenon. This is because the numbers of American migrants are falling sharply.” [ source ]

This last March I reported that due to the Covid pandemic (probably) the usual annual census of overwintering Monarchs in Mexico had either not been completed or had not been reported.  Now, at last, the WWF, in conjunction and partnership with:

[These are, left to right, the Secretariat of Environment and Natural Resources (Mexico), the National Commission of Natural Protected Areas (Conanp), the Monarch Butterfly Biosphere Reserve, World Wildlife Federation, and the TELMEX Foundation.]

has finally, issued the annual report as a four-page .pdf file.

Good News!

Executive Summary

During the second half of December 2021, 10 colonies of Monarch Butterflies were registered covering 2.835 hectares (ha) [about 7 acres] of forest, this represents a 35% increase in relation to the area registered in 2020 (2.10 ha). Six colonies covering 2.174 ha were located inside the Monarch Butterfly Biosphere Reserve (MBBR) and four covering 0.661 ha were located outside the MBBR, five of those colonies were located in Michoacan and five in the State of Mexico.

The increase by 35% is far from the 100-times increase seen in the California migration, but is still good news.  The Eastern Monarch migration still has a long way to go to return to the numbers seen in the 1990s.

This year’s count was not quite as high as the one-site estimate of “doubled” reported to me by Joel Moreno Rojas who operates the JM Butterfly B&B in Macheros, Mexico, adjacent to the Cerro Pelón reserve.  Cerro Pelon did have the second largest colony this last year, exceeded only by Sierra Campanario.

Monarch experts are not in agreement about what has caused either the near-disastrous low of 2013-2014 or the recent improvements.  Most agree on the major culprit for the population decline since the 1990s – changes in agricultural practices, including the use of Roundup-type herbicides which greatly reduced the incidence of milkweed among field crops, like corn,  and began to be used to eliminate roadside weeds in addition to the usual mowing.  The aggregate effect on milkweed populations, necessary food for monarch caterpillars, can be seen in the monarch migration numbers.  This is known as the “milkweed limitation hypothesis.”

Chip Taylor, director of Monarch Watch, recently completed a study that found that numbers of monarchs overwintering in central Mexico is directly tied to the size of the summer population in the U.S. Midwest.

Published Aug. 7 in the journal Frontiers in Ecology and Evolution, the researchers show that the decline in the monarchs’ overwintering numbers is not due to an increase in the deaths of monarchs during the migration — the “migration mortality hypothesis.” The main determinant of yearly variation in overwintering population size, they found, is the size of the summer population.

The “migration mortality hypothesis” has been heavily promoted in Science and Scientific American.  This hypothesis aligns well with the narratives of Climate Change advocacy and goes like this:  “changes in the climate are causing bad weather during critical monarch migrations time windows with more damaging storms, droughts, high winds and climbing temperatures.”  However, Chip Taylor and his colleagues found:

“Showing the migration mortality hypothesis advocates their assumptions were wrong took awhile since that required a significant effort to vet our monarch tagging database for accuracy and to analyze the data,” Taylor said. “Dealing with 1.4 million records is no simple task.”

“In contrast to the predictions of the migration mortality advocates, the tagging recoveries — a measure of migration success — did not decrease over time, the researchers found.”

“In addition, the number tagged each year was correlated with the size of the overwintering population in Mexico, consistent with the milkweed limitation hypothesis. The tagging also confirmed that the majority of monarchs reaching the overwintering sites originated from the Upper Midwest.”  [ source ]

The Monarch Watch study reinforces the need to restore milkweed to its original range and numbers.   Restore milkweed, restore the monarchs.

Monarchs have painted themselves into a corner by requiring milkweed for reproduction.  This was a perfectly fine idea when milkweed grew almost literally “everywhere”.  It is still widespread but not nearly in the numbers seen in earlier decades. In the American Mid-West, the milkweed that would be maturing in the vast cornfields never got past seedling stage due to Round-up Ready agriculture.  In my area, roadsides and highway verges, where milkweed flourishes, are generally mowed down in the late summer coinciding with the exact time that the caterpillars that will become the migrating super-generation of monarchs are on the milkweed plants.

All-in-all, this is encouraging science news, Western Monarchs have surged in some mysterious way, Eastern Monarchs are recovering, and the need to plant more milkweed has been established through rigorous painstaking science. 

Bottom Line:

1)  Migrating monarch populations are recovering – though the underlying reasons for the dramatic recovery in the West is a mystery.

2)  The actions needed to restore monarch migrations to the previously seen numbers are clear: a) encourage local and state agencies to cease mowing milkweed patches along highways with special emphasis on the Midwest,  b) assist Mexico to fight the illegal logging in monarch reserve areas of Mexico.

and

3)  You can help by planting beautiful native milkweeds at your home or encourage your local parks department to plant them in public gardens. Native Milkweeds are available from many commercials seed and plant companies such as Spring Hill, Select Seeds, Gardens Alive or American Meadows.  Search the ‘net for “buy native milkweed seeds and plants”.

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Author’s Comment:

My wife manages a small public garden as a volunteer at our local public-access boat launch on the river.  We encourage a few native milkweed to grow as tall background flowers and have a few in our yard.  They actually grown best in the “worst” places which is why they are often found on highway verges and abandoned fields.  She also plants a few vegetables in amongst the flowers for the amusement of visitors – free cherry tomatoes for the pickin’. 

My fascination with Monarch Butterflies dates back to my youth in Los Angeles, California, where Monarchs and Swallowtails can be found year around. 

Monarch Watch does good work – like proving that climate change is not responsible for the decline of the monarchs —  it also makes milkweed available through their Milkweed Market and through a program for their Free Milkweeds for Restoration Projects program. 

I generally do not approve of international scale environmental organizations like WWF (which brags that 82% of its donations go to environmental programs, which is “pretty good” – in contrast, the charity my wife and I worked for in the Dominican Republic spent 100% of all donations on direct help programs, the overhead cost being covered by separate funding.)  But WWF in Mexico does good work and is a prime mover in protecting the Monarch preserves in Central Mexico.

My other essays on Monarchs are found here.

Thanks for reading.

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