The presence of monarch butterflies in Mexico’s oyamel fir forests this past winter was 22 percent less than the previous year, according to the most recent survey led by the World Wildlife Fund (WWF) Mexico. Monarch butterflies occupied 2.21 hectares, 0.63 less than the 2.84 hectares in the 2021-2022 overwintering season. (Monarch Joint Venture)
From Chip Taylor of Monarch Watch, University of Kansas regarding population development this year.
How well the monarch population will develop this spring will largely depend on:
1) The timing and number of monarchs arriving in Texas in March and April (most areas of the state are listed as being in extreme drought, but my sources tell me that vegetation was two weeks ahead of last time.)
2) the temperatures encountered during this interval
3) the number and latitudinal distribution of eggs
4) the abundance, distribution, and quality of milkweeds
5) the abundance of predators and parasites, and
6) the temperatures that occur during May and early June that enable or restrict the recolonization of the northern breeding areas by first generation monarchs.
Listing the factors is easy, but getting the data to interpret how each year works out is difficult. We need help in the form of lots and lots of observations by citizens.
Journey North and iNaturalist
1) First sightings reported to Journey North in Texas provide data on timing and numbers.
2) Similarly, first sightings tell us a great deal about the colonization of the summer breeding areas.
3) The number and distribution of eggs can be inferred from the distribution of first sightings.
4) The postings to iNaturalist tell us a lot about the abundance and distribution of milkweed species.
5) There is no place to report data on the abundance of predators and parasites.
What we think we know is that predators generally decline with the length of drought periods. If true, survival of monarch immatures in March and April may be greater, enabling more first-generation offspring to reach maturity and to fly north in May. Otherwise, all of the above can be linked to weather data, and there is lots and lots of that.
I see two positive signs in the data to date:
1) monarchs didn’t arrive too early like they did in 2012, and
2) the advance through Texas will be slow with few monarchs reaching 35N (Oklahoma City) by April 1. (The will mean that most of the eggs will be laid in Texas and southern Oklahoma where temperatures are warmer – assuring faster development – than farther north.)
Eastern population development this year
In the east, the second generation is on the wing. Some began emerging around the 10th of July, and others have yet to take flight. The eggs laid by this cohort from mid-July to about the 10th of August will become the third generation – the migratory generation. The size of that generation will largely depend on the temperatures, nectar availability, and quality and abundance of the milkweeds in the breeding areas north of 40N. (Roughly a line from St. Joseph, MO, to Philadelphia.)
At this writing, there is reason to believe that the migratory population will be similar in numbers to those of most of the last decade – namely a population large enough to produce an overwintering population of 2-3ha in Mexico.
There has been a sameness of this breeding season to many others except for two things:
1) the number of first sightings in Texas was lower than average, and
2) the number of monarchs reaching the prairie provinces has been exceptional.
For more on the latter see the recent blog post Monarchs: Reaching 50N and beyond.