Bring Back the Monarchs – 2023 Update

Create, Conserve, Protect…

The Monarch butterfly migration is a phenomenon, mainly across North America, where millions of Monarchs (Danaus plexippus) migrate from the United States and Canada to mountains in central Mexico, where they wait out the winter until conditions favor a return flight in the spring. Eastern Monarchs spend summers east of the Rocky Mountain range and travel over 3,000 miles to overwinter in Oyamel forests in the mountains of Central and South West Mexico. The western Monarch population spends summers west of the Rocky Mountain range in North America and overwinters in California along the Pacific coast near Santa Cruz and San Diego. 

The monarch migration is truly one of the world’s greatest natural wonders yet it is threatened by habitat loss at overwintering grounds in Mexico and throughout breeding areas in the United States and Canada. Monarch butterflies have declined an average of 80% over the past 20 years. From the 1990’s to the 2020 winter count, the Eastern Monarch population has declined from 1 billion to 155 million butterflies.

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Monarch Population Status – 2023 Update from Dr. Chip Taylor, Monarch Watch (monarchwatch.org)

Eastern monarch population

The Journey North program ( https://journeynorth.org ) has been recording monarch first sightings for 23 years. It’s an awesome record with a number of uses. Out of curiosity to see how first sighting this year in NE Kansas compared with other years, I skimmed through those records. This year the first monarch to appear in the Topeka, Lawrence, Kansas City area was spotted on the 10th. That is early and by the 18th there were a number of sightings. Checking the records revealed that more than one sighting by the 18th of April has only occurred in 7/23 years. In other words, the number of monarchs to reach our area is so few in most years that we simply don’t encounter them, or they may not even be this far north.

While I have been watching the first sightings accumulate in space and time this year, I’m finding it difficult to assess what the data mean. The numbers for Texas are down. That could mean the population is down, with fewer returnees or it could mean that monarch activity was low due to cool weather so fewer were seen. The latter seems possible since I’ve seen a number of reports by observers that mention the sightings of many monarchs over time or on single outings. While some of the monarchs arrived ahead of the emergence of milkweeds in some areas, it appears that the majority of eggs laid by returning monarch were laid in Texas, where due to slightly warmer temperatures, the larvae will develop faster than if the eggs were laid further north. I’ll need to look more closely at the data, but overall, the colonization by the returning monarchs fits a common pattern and there is no reason for concern at this time.

Western monarch population

The population rebound over the last two years in the West has been remarkable. The numbers counted at all known overwintering sites last November exceeded 335K. This was the largest population recorded since 2000 – a mere 22 years. How is that possible, and what does it mean for the future? Can we expect similar numbers or even more monarchs in November 2023? Probably not. The population is certain to be lower for a number of reasons, but how much lower and where will the monarchs originate from that reach the overwintering sites?

The western population development, like that of the east, is largely driven by the weather. So, the immediate question is are the weather patterns from last November to the present similar to any year in the past and the answer is yes. The winter and spring of 2006 in California was cold, though not as wet, as that of 2023. The temperature patterns were quite similar. Statewide the three-month interval from January through March was the coldest since 1955 and one of the wettest as well with many strong storms. These conditions had to take a toll on the overwintering monarchs and certainly reduced the number of females available to begin egg laying as the weather warmed, but when did that begin? In most years, especially recently, mating and reproduction begin by mid-March and sometimes earlier. This year the mean temperatures for March were 44.2F vs 44.0F for 2006. These were the 4th and 5th coldest March temperatures in the record that goes back to 1895. April started out cool in both years with temperature increasing in the last 10 days of the month (based on the 10-day forecast for this year). So, given these extreme conditions, how much reproduction has been possible to date this year? There are no data on this point.

Again, looking to 2006, at the end of the migration the count was over 200K. Will the numbers reach 200k this year. Maybe, but I’m skeptical. In most years, first generation monarchs would begin emerging in the next week and would begin moving into the Sierra foothills and beyond into Nevada and the inner mountain west. Some would begin moving in May toward the NW as well. Movement out of California looks to be limited for some time due to cold conditions in both the Sierras and to the north. If these conditions continue, most of the overwintering monarchs in November will have originated from California. This was first suggested by Paul Cherubini, a long-term observer of monarchs in the west, in a post to the Western Monarchs email list ( https://groups.io/g/WesternMonarchs ) on 5 April. Paul maintains that the population could “produce an overwintering population roughly as large as the past two winters”. That would surely be an interesting outcome.

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Reasons for the Decline

According to Dr. Chip Taylor, “We are losing habitat in this country at a rapid pace of 6,000 acres per day, or a loss of 2.2 million acres per year. Further, the overuse of herbicides along roadsides and elsewhere is turning diverse areas that support Monarchs, pollinators, and other wildlife into grass-filled landscapes that support very few species. The adoption of genetically modified soybean and corn have further reduced Monarch habitat. Climate change impacts Monarch Butterfly migration patterns and, in turn, their survival. Not only does climate change influence climate cues that Monarchs use to navigate and begin their migration, but it also impacts their food sources and overwintering habitats. If these trends continue, Monarchs are certain to decline, threatening the very existence of their magnificent migration.”

Whether monarchs rebound this year will depend on the number of returning monarch females, nectar and host plant availability, March and early April temperatures, and then the conditions from May to September.

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Create, Conserve, Protect Monarch habitats

To restore habitats for Monarchs, pollinators and wildlife in general, Monarch Watch has a nationwide landscape restoration program called “Bring Back the Monarchs”. The goals of this program are to restore 20 milkweed species to their native ranges throughout the United States and to encourage planting of nectar-producing native flowers that support adult Monarchs and other pollinators.

You can help!

Monarchs cannot survive without Milkweed plants, as it is the only host plant eaten by newly hatched Monarch eggs and caterpillars, but you can help! By planting Milkweed with some of the Monarch’s favorite nectar producing flowers every year in your yard, garden, or community, and reducing or eliminating the use of pesticides and herbicides, you will be providing food and shelter for Monarchs and other native butterflies and bees. I truly believe that by caring for native wildlife in our own backyard or in our community, each of us can make a difference and keep these beautiful butterflies alive for future generations!

Perennial Host plants for Monarchs – Butterfly Weed (Asclepias tuberosa), Common Milkweed (Asclepias syriaca), Swamp Milkweed (Asclepias incarnata)

Annual and perennial Nectar plants – Zinnia (Zinnia elegans), Mexican Sunflower (Tithonia), Joe Pye Weed (Eupatorium purpureum), Purple Coneflower (Echinacea purpurea), Indian Blanket (Gaillardia pulchella), Pincushion Flower (Scabiosa), Bee Balm (Monarda)

Planting and Growing Directions for Monarch Host and Nectar plant

Links and Resources

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