Guest Essay by Kip Hansen — 4 February 2024 – 1000 words/5 minutes
When we say that “science is never settled”, we mean that there are always new things to be discovered, new insights to be gained, new ways of looking at the same old things and thus, there will be disagreements, challenges to the old ways of seeing things, and controversies. That’s a big part of what makes science interesting to me and why I write about it.
Here at WUWT, I write, once or twice a year (or here), about the mighty and mysterious Monarch Butterfly and its incredible migration every Spring from the Central Mountains of Mexico north and east into the U.S. heartlands, and up into the plains of Canada and then, in the Fall, back again to Mexico. No butterfly that leaves Mexico ever lives to return, but some of their great-great-grandchildren do. There is a similar but much smaller migration on the West Coast of North America that ends in the coastal range of California.
In the worlds of entomology, ecological conservation and threatened and endangered species, there is general agreement on some points about monarchs
1) The number of monarch butterflies that have been migrating to overwintering grounds have sharply decreased from the very high numbers seen in the 1980s and 1990s.
2) Agricultural practices on the great plains of North America and elsewhere have changed to include the use of weed killing agents (Roundup) that have eliminated the once plentiful milkweeds that in the past co-inhabited fields of corn and soy beans. Milkweed is important as monarchs lay eggs only on milkweeds and monarch larva (caterpillars) only eat milkweed leaves.
3) There are a great many advocacy groups oriented to “saving the monarchs” – some are science-oriented and do monarch tracking, counting and tagging. Some encourage rearing monarchs or gathering and protecting monarch chrysalises until the butterfly emerges. Some encourage planting milkweeds and “butterfly gardens” and supply milkweed plants or seeds.
4) Commercial enterprises have arisen that mass breed monarchs (and other butterflies) either for scientific purposes (biology or nature classes) or for sale to be released at celebrations such as weddings. [examples, not recommendations: here and here ].
Well, that is part of the controversy. Read on to find out why.
What parts of the general view are controversial? All of them – yes, even the first one on migrating monarch populations.
Let’s start with #1, migrating monarch populations.
This is the short-term graph of the Western Migration, which is considered to be most imperiled. Previous years were a great deal higher. As is obvious, the 2020-2021 New Year’s count, which is meant to reflect the number of monarchs roosting on New Year’s Day and thus having survived the California’s winter months, was so close to zero that many monarch watchers thought the Western Migration had finally reached practical extinction.
The recovery seen in 2021-2022 was considered miraculous and is still largely unexplained, though experts have weighed in. Chip Taylor, of monarchwatch.org, makes the following observation:
“There have been many attempts to explain this rate of increase since it’s impossible for a cohort of 1849 overwintering monarchs to initiate a cascade of reproduction over 3-4 generations that would result in a large fall migratory population. This result is improbable since the number of surviving females would have been less than 600, and the known rates of mortality for all life stages indicate that rates of increase are strongly constrained. Clearly, the population growth in 2021 was initiated by thousands of females, perhaps 10s of thousands. The need to understand the increase leads to questions about where those females came from.”
Taylor then references Fisher et al. (2018) which states:
“Our results suggest that estimating the size of the western overwintering population in the future will be problematic, unless annual counts compensate for a shift in the distribution and a potential change in the number and location of occupied sites.Why is this important? The count of Western Monarch migration is done by volunteers that visit know roosting sites – known from past years – and the number of sites visited changes from year to year. (see the grey trace in the chart above). So, if the overwintering monarchs have moved to new unknown sites, they can’t be counted unless accidentally discovered. Fisher et al. posit that if the lower coastal roosting sites are too warm, the monarchs will roost higher up in the coastal range where it is cooler.
And that means that the counts of the Western Monarch migration may be less useful in determining the migrating population.
The same may be true for overwintering roosts in the Mexican mountains as well. The official report, “AREA OF FOREST OCCUPIED BY THE COLONIES OF MONARCH BUTTERFLIES IN MEXICO DURING THE 2022-2023 OVERWINTERING PERIOD”, includes this figure:
And gives their counting methodology as follows:
“Starting in December, each of the 13 overwintering sanctuaries inside and outside of the “Monarch Region” were visited twice a month; when a colony was found its location was established with a Garmin® Geopositioning device in UTM projection, with WGS84 datum. The perimeter of the forest occupied by the butterflies was determined from the tree that was found on the highest point of the slope, then we recorded the direction and distance of the consecutive and peripheral trees of the colony. The polygonal perimeter data was processed with the ArcView3.3 geographic information system (GIS) to establish the area occupied by the colonies (Vidal y Rendón-Salinas,2014). The Atlautla colony was also visited, whose area is not counted in the historical graph as it is located outside of the Monarch Region.”
It is clear that the overall Monarch Region is three times the size of the protected area. There are three known (and thus counted) areas of monarch overwintering roosts. But it is unknown how closely the 168,000 hectares (415,000 acres) is searched for new or novel roosts, or if such search is done at all, similar to the problem in California’s coastal mountains.
Even UNESCO seems to believe that there may be other overwintering roosts not inside of the Monarch Biosphere Reserve “Up to a billion monarch butterflies return annually, from breeding areas as far away as Canada, to land in close-packed clusters within 14 overwintering colonies in the oyamel fir forests of central Mexico. The property protects 8 of these colonies and an estimated 70% of the total overwintering population of the monarch butterfly’s eastern population.” [ emphasis nine – kh ]
If Fisher et al.’s hypothesis is correct, it will be necessary to do substantial searches of suitable eco-niches for overwintering monarchs, both in California and Mexico in order to establish more correct counts. If this is done, it can only add to the numbers of overwintering monarchs in both areas.
Bottom Line: On the issue of Overwintering Populations, #1 on our list of some points of general agreement, it is believed that overwintering populations are down, but the California experience in 2020-21 to 2021-22 shows that even this might not be true. Overwintering populations may have simply shifted their geographic positions slightly and escaped counting. In the case of California, there had to be substantial uncounted roosts.
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Author’s Comment:
When I dig in on almost any science topic, if I dig in deep enough, I find that ‘the science’ does not even agree with itself. The more honest a science field is, the more disagreement, the more disparate viewpoints, and more controversies, big and small, are found. This is healthy sign and a good omen.
Monarch Science, five or ten years ago, was one big happy family, everyone agreeing that the Monarch were doomed unless we humans changed our evil ways and cancelled Monsanto. This is no longer the case.
Dr. Roger Pielke Jr. has a substack post today titled: “The Weaponization of “Scientific Consensus”. So far, consensus enforcement is not happening in entomology. But the consensus viewpoint is all one sees in the MSM.
More to follow on the remaining three points on our list.
Thanks for reading.
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