Have you seen many monarch butterflies around this year?

A once plentiful species has lost approximately 99.9% of its western population since 1980, with its eastern population – the monarchs we see in London, Ontario – declining by 85% between 1996 and 2014. That’s less than 20 years. This sharp decline was recognized federally in December 2023, when the Government of Canada listed the monarch butterfly (Danaus plexippus) as an endangered species under the Species at Risk Act (SARA) [1].

The monarch butterfly is often one of the first ways many find excitement and interest in the environment, however the reason their population can change so dramatically is less well understood. In this blog post we’ll dive into why this species struggles to find safe spaces when crossing two federal borders, and what their decline says about the health of migratory species and pollinators. As well, Evan Bennett, current Master’s student of Professor Nusha Keyghobadi at Western University, shares his perspectives after a summer of sampling and identifying butterflies in the Canadian Rockies.

Multi-generational Migratory Monarchs

Since their migration patterns were discovered in 1975 by Dr. Fred Urquhart (University of Toronto) and Norah Urquhart [2], monarch populations that previously were in the millions hit record lows. While eastern populations are slightly more stable, only 30,000 monarchs overwintered from 2018-2019, with that number dropping to 1899 in the fall of 2020, the lowest in recorded history of western North America [3]. However, this population made a dramatic recovery in the following years, coming back to 247,246 in 2021 and 335,479 in 2022 [3]. This kind of rapid population fluctuation is really shocking to witness, but can be explained by the unique multi-generational migration patterns of the monarch butterfly.

“There’s not many migratory butterflies, and even less long-distance migratory butterflies.”

A common misconception about monarch butterflies is that one monarch is going to make that full 3000 kilometer migration from North America to Mexico, when in fact they require multiple generations to make this journey. To be precise, four generations of monarchs are required to make the full annual cycle [4].

In the fall, the longest lived generation typically known as the fourth generation, flies due south where the Eastern population will roost in Mexico, and the Western population overwintering along the California coastline. The following generation, known as the 1st generation, travels north from there to the southern United States. The following two generations continue moving north, looking for their only food source and reproducing at any location with milkweed. “They’re constantly laying eggs throughout their migration,” says Bennett, “and if any major event happens at any stopover site, you’ll have a major dip in population.” After three cycles we return to our fourth generation monarchs, who then have to make the final leg of the return journey their great-great-grandparents made and start this cycle all over again [4]. This kind of multi-generational travel is pretty uncommon, as “most butterflies lay their eggs under fallen leaves before the snow cover,” Bennet notes.

However, you can see how if anything happens to any one group of these four generations, a huge ripple effect can substantially affect their populations. Bennett further clarifies this point: “every time the generation rolls over, they need a stable spot because they have to lay eggs, those caterpillars have to eat and form a chrysalis, hatch, and then feed as butterflies to be able to continue their migration.” The rapid loss of their only habitat, milkweed, coupled with the increasingly unpredictable weather events from climate change leads to a cascading loss of this easily identifiable species.

The Monarch as a Flagship Species

With many people across a whole continent finding joy and curiosity in these magnificent orange species, the monarch butterfly has become one of the best known flagship species. They offer an easy to spot introduction to the natural world, potentially inspiring individuals to participate in citizen science apps and other environmental initiatives. “People see these bright orange butterflies, and it gets them interested in other environmental actions. That’s how I remember getting interested in them when I was younger.”

Conservation of these migratory butterflies is bigger than just this species. As one of the best tracked and most easily identifiable species, their rapid decline leads to questions about the decline of the less tracked, less identifiable species. We can specifically have an impact here in London, Ontario, as Bennett lets us know that “the migration path is right through London, and backyard plants do genuinely help this species.” Ensuring you leave native species long and untrimmed – specifically milkweed plants – will further provide nesting sites for other butterfly species, making your yard a biodiversity hotspot year round. Make sure you keep these butterflies wild, as captive-rearing of wild butterflies can have unintentional harmful ripple effects [5],

How can we Help Protect the Monarch Butterfly in London, Ontario?

“Theres lots of butterfly outreach events, whether you’d rather tag the butterflies, or plant native species, there’s always organizations looking for people to help monitor their native plants and species,” says Bennett.

Start taking action and supporting monarch populations in and around London, Ontario, by planting milkweed in various points around your yard. Common Milkweed, Butterfly Milkweed, and Swamp Milkweed are three native species you can find at many nurseries and seed-swap events. As well, using citizen science apps like iNaturalist to report any monarch sightings provides invaluable information to researchers like Evan Bennett, and helps keep real-time records of how these populations move.

If you’d like to get involved with us, learn more about our program offerings, including ones that support residential ecological restoration at Thriving Communities, or follow us on social media to stay informed about upcoming events!

Sources:

  1. Canada, E. and C. C. (2024, July 18). Government of Canada. Canada.ca. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/factsheets/monarch-butterfly.html
  2. Parks Canada Agency, G. of C. (2024, September 17). Monarch butterflies at Point Pelee National Park. Point Pelee National Park. https://parks.canada.ca/pn-np/on/pelee/nature/faune-wildlife/monarque-monarch
  3. James, D. G. (2024). Monarch Butterflies in western North America: A holistic review of population trends, ecology, stressors, resilience and adaptation. Insects, 15(1), 40. https://doi.org/10.3390/insects15010040
  4. Migration. Monarch Joint Venture. (n.d.). https://monarchjointventure.org/monarch-biology/monarch-migration
  5. Pelton, E., & Authors Emma Pelton Senior Endangered Species Conservation Biologist . (n.d.). Keep monarchs wild: Why captive rearing isn’t the way to help monarchs. Xerces Society. https://xerces.org/blog/keep-monarchs-wild#:~:text=These%20concerns%20include%20the%20risk,adverse%20effects%20on%20wild%20populations.