The size of the overwintering population of Eastern monarch butterflies was just released on Feb 25, and the number shows yet another decline (to a total of 2.1 hectares/ 5.2 acres; details are shown in the figure below). What does this mean for the Adirondacks this coming summer? Monarchs were abundant in the Adirondack region in 2018, just as they had been decades ago, but 2021 will be a year of many fewer, just as it was in 2020 and most recent years.
Monarchs are in decline because of multiple threats throughout their life cycle: the loss of milkweed because of industrialized agriculture in their main midwestern breeding area; logging of the overwintering forests in Mexico; drought and loss of nectar sources due to climate change; and increasing severity of killing storms.
Recently the US Fish & Wildlife service declared monarchs to be “warranted but precluded” for listing under the Endangered Species Act. That decision is well explained at: https://monarchjointventure.org/blog/faqs-endangered-species-act-listing-decision-for-monarch-butterflies. It means that the federal government will take no actions for the time being to reverse this decline even though the current figure of 2.1 hectares is much below the estimated number of 6 hectares required to sustain monarch migration.
There is uncertainly, of course, about what we will we see this summer. Will the severe cold in Texas of the past two months further depress this year’s monarch abundance by slowing the growth of milkweed and nectar sources needed for the northward migration? Will summer weather in the Adirondacks be moderately warm, which is ideal for monarchs to lay many eggs and increase the numbers we see? Although our area is not the region of most reproduction, milkweed grows well here. Will warmth in the fall delay the return migration, giving us late sightings into October?
Here’s a reminder of when we’ll first see monarchs. Those butterflies that survive the winter in Mexico begin migrating northward in February and March and lay eggs in Texas and the southern tier of states. Monarchs that emerge from those eggs complete the northward migration into the breeding region of the central U.S. and southern Canada. Their offspring spread out in multiple directions where there is milkweed, including the Adirondacks, and that is the generation we usually first see. Additional generation(s) add to overall abundance, so we see more monarchs in August than at any other time of year.
Keep an eye out for monarchs this summer. Those you see reflect underlying changes in the environment around us.
The above figure of overwintering monarch abundance is courtesy of the Monarch Butterfly Fund (www.monarchconservation.org). Photo at top by Ernest H. Williams