Rebounding monarch population heads southwest – but there could be trouble ahead
They seemed to be everywhere in central Pennsylvania this summer — monarch butterflies, that is — those bright orange and black winged jewels that float on air. It is refreshing to see so many, and I have been seeing them since June. Following a successful reproductive summer, their numbers are highest now as the population prepares to migrate southwest — all the way to the mountains in Mexico.
On Aug. 17, we counted 40 adults on a five-mile hike that four of us took on state game lands. These monarchs were feeding, mating and the females were busy laying eggs. I have observed monarchs everywhere that I have been during the past six weeks — Blair, Cambria, Dauphin, Huntingdon, Juniata, Lancaster, Mifflin and Centre counties, as well as in Virginia and Delaware.
For comparison, just a few years ago, I spotted my first monarch butterfly of the year while on vacation in Delaware in August. I only saw three monarchs in Pennsylvania that entire year.
The butterflies that overwinter in Mexico begin the journey north in early spring, but it takes several successive generations before the first monarchs make it all the way to Pennsylvania. When they get here, they eat, mate and reproduce. Some head farther north into Canada and New England.
Adult monarchs have been visiting the milkweed patches on my Bald Eagle Valley property all summer. During the past month, we have discovered more of the yellow, black and white-striped caterpillars and green chrysalises (also called chrysalides) on my property than ever before. It is these monarchs — the adults that are emerging from their chrysalises in September — that will make the journey south.
It is not just my observations indicating that the monarch population is rebounding. The numbers released in January by World Wildlife Fund Mexico showed a 144 percent increase over their population in 2018. Scientists from that organization measure the area of forest occupied by the clustering butterflies on their winter roosts. Their 2019 count found 14 colonies with a total area of about 15 acres — the largest area measured since 2006. A football field including end zones measures 1.23 acres.
Monarchs populate most of the United States and southern Canada during the summer. To make predictions on the status of the overall population, one must have a continental view, not simply a local snapshot. The population has been dangerously low since 2010. Last winter’s data was a bright spot. As recently as the mid-1990s, monarchs covered nearly 52 acres of forest in their wintering ground, falling to less than 3 acres in 2014.
Chip Taylor, who heads Monarch Watch at the University of Kansas, has made a science of predicting what this winter’s monarch population will look like. By early May, based on data collected up until that time, Taylor had predicted a downward trend to between 9.9 and 12 acres, with the population likely to be closer to 10 acres. This was followed by favorable conditions during May, June and July. By early August, Taylor had upped his prediction to 12 to 15 acres, with the expectation of it being closer to 15.
“The population is booming in the northeast right now,” Taylor said in a telephone interview in late September. “I have had very positive reports from Maine, New Hampshire, Connecticut, Massachusetts, Pennsylvania and parts of New York.”
Taylor expects a large migration of monarchs through Pennsylvania, and he noted that the migration southwest is beginning late across the United States. Based on my observations, the migration in central Pennsylvania began Sept.26.
“I expect the migration out of the northeastern states to be as big as the one in 2015 or maybe as large as 2012,” he predicted.
So has Taylor upped his over-wintering prediction yet again? — No — there are just so many variables that could work in favor or against the monarch butterflies.
“The migration is bordering on 12 days late — which historically does not bode well for the butterflies,” he said. “I am also worried about the semi-drought conditions in Oklahoma and parts of Texas. All of the monarchs from the northeast and midwest have to migrate through there, and the lack of nectar-bearing plants in that region could really reduce the population.”
Sadly, the plight of the monarch butterfly has been serious enough to consider inclusion on the endangered species list. David Mizejewski, Naturalist with the National Wildlife Federation, commented on their status.
“We still have a lot of work to do before the species is fully recovered — including creating more habitat, reducing the use of harmful pesticides and addressing climate change — but this summer’s population is a good indicator that our work is starting to show results.”