InsectNet forum

The plight of the beloved Monarch Danaus plexippus has long drawn concern, and likely for valid reasons. However, reports of the species' demise are rife with, at least, sensationalism and deficient scientific reporting.

Case in point: "Danaus plexippus (Monarch Butterfly) populations in North America east of the Rocky Mountains are in decline due to loss of habitat containing Asclepias ssp. (milkweed) and blooming forbs." Fisher, Snyder & Bradbury. "Blooming Forbs Utilized by Breeding-Season Danaus plexippus in the USA North-Central Region" LepSoc 77, March 2023.

Not to pick on these authors, this is but one of many publications that make broad sweeping statements. Most readers will remember the recent hysteria that the Monarch population out west was headed for extermination due to global warming, to the point it was considered for listing under Endangered Species Act- then the population suddenly rebounded.

Still, the claim that Monarch populations east of the Rockies are in decline is geographically broad. And, from a perspective I've rarely seen, over what period?

Assuming Monarchs everywhere east of the Rockies are indeed in decline, is it a problem to the species, or an inconvenience to humans?

To wit: There were zero Monarchs in northern New York and Southern Ontario 10,000 years ago. The region was covered by a sheet of ice.



Well, some will say, that was the ice age. OK then:

"For at least 5,000 years prior to European settlement, it’s estimated that 95% of the Northeastern United States (the Northeast) was covered by forest." https://www.newyorknature.us/woodlands/



Asclepias doesn't grow in shade. So, before Europeans, the virgin forests limited Monarchs to 5% of NE USA; actually less, once one also discounts mountain tops and oak savannahs...so what was the range then, maybe 1% of New England?

Meaning there were few, if any, Monarchs in Upstate NY or Ontario Canada when the Europeans arrived. The monarch populations followed the expansion of Asclepias that accompanied the near-total deforestation. I've oft wondered the same about restoration of open grasslands which almost invariable also note that the scientists have to keep the forest back...but wait, wouldn't forestation be a natural progression? Was this area forested prior to Europeans?

The authors I picked on above do present their arguments concerning the causes of a decline in the eastern Monarchs, focusing their paper on "North Central" overwintering areas...but that's not what they stated in the quote I opened with. If one is going to make a broad statement, one should then continue with that.

Still, I wonder- why do we care so much about "North East" monarchs, which are astronomically more abundant than they were 150 years ago, and ignore Saturnid populations which have crashed?

People notice butterflies. You can also use animal populations to support your agenda. I think 400 years ago, a lot of the area east of the rockies was
probably covered in different vegetation, as easily as I'd assume milkweed can colonize an area, the butterflies would follow. I haven't seen a monarch
butterfly in Oregon for a very long time. We're on the way to the overwintering grounds too.

kevinkk wrote: Tue May 16, 2023 1:23 am People notice butterflies. You can also use animal populations to support your agenda. I think 400 years ago, a lot of the area east of the rockies was
probably covered in different vegetation, as easily as I'd assume milkweed can colonize an area, the butterflies would follow. I haven't seen a monarch
butterfly in Oregon for a very long time. We're on the way to the overwintering grounds too.

East of the Rockies had different flora coverage, but the NE was from ~8000 BC to 1400 nothing but virgin hardwood, and endless canopy. Milkweed would have been limited to creek edges. Milkweed does travel well as a seed, so if there was milkweed, it could have been scattered, but quite rare, throughout NE USA and southern Ontario CA.

It then would be an interesting study to determine how the symbiots milkweed & monarch got from zero to migration paths in NE. Circa 1200 the Iroquis nations cleared a LOT of area for agriculture, so certainly by 1600 or so there would have been plenty of open space for M&M. By 1900 NY and southern Ontario were almost completely denuded, so the region was ripe for M&M to explode in population.

I have a hard time envisioning the six monarchs living in Ontario Canada in 1200 migrating every year. But clearly, by circa 1900 they were in NY and ON, and migrating. If one suspects that the indigineous tribes' clearings weren't support much of a population, that means that the M&M populations really didn't expand until circa 1800, when serious logging began. How long did it take the population to reach what it was in 1970? Was that the maximum, which is now in decline due to reforestation and other factors?