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Where are the Monarchs?

August 20, 2020

By Karin Davidson Taylor, Education Program Officer, Royal Botanical Gardens.

More than once this summer, I’ve heard the comments, “I haven’t seen as many Monarchs this year as last.” Or “I didn’t see any Monarchs until later compared to last year.” Last year was a wonderful year for Monarch butterflies. At Royal Botanical Gardens, we first observed them in 2019 near the end of May, whereas this year, our first observation was almost three weeks later. Was it because some of us were working from home, and so missed seeing them? No, it turns out that the Monarchs’ return was late across the province. When looking at the Journey North map for first spring sightings, there were Monarchs in Ontario from Point Pelee all the way to Sioux Lookout, only by the first week of June. Why did they arrive later this year, and what factors affect the health of the Monarch population?

Monarch eggs on milkweed
monarch caterpiller on milkweed in field

A little background: Since early June in Ontario, we’ve seen at least 2 generations of Monarchs. Those eggs and caterpillars that you are seeing now in your gardens are a third or even fourth generation and are known as the super-generation. This generation has an astonishing life span of 8-9 months compared to the 6-8 weeks of the earlier summer generations. Their larger size is due to increased body fat needed to fuel the 5,000 km migration down to Mexico. After overwintering there, they migrate again, to Texas, where they will mate, lay eggs, and die. This is the beginning of the multiple-generation journey to Ontario and other points in Canada east of the Rockies. Imagine, the Monarchs we are seeing now could be the great-great grandchildren of last September’s Monarchs!

What is Affecting Monarch Numbers?

There are a few factors that can affect the numbers we see locally including climate and available habitat in the United States and Mexico. The climate and available habitat in Ontario and along the southbound journey through the US, the conditions in the Oyamel fir forests in Mexico, and conditions as the new generations make their way north to Ontario all pose challenges for this species. When looking at the numbers of overwintering Monarchs in the 12 mountaintop locations in Central Mexico in 2018–2019, there were an estimated 225 million individuals covering over six hectares. Things were looking good — we had high hopes for a banner year. We weren’t disappointed when it came to numbers arriving in May 2019, but for some reason this did not translate to numbers migrating in Fall 2019 and overwintering this last winter (2019–2020). Compared to the previous year, only half of the survey area in Mexico was populated by migrating Monarchs.

Monarch butterfly on verbena bonariensis

Weather can impact the survival and migration timeline of Monarchs. Will it be too hot and dry, or too cold to fly and feed? Scientists were concerned that the cold snap experienced in the southern US may have slowed the migration. What is interesting is that the temperatures observed in Texas in March may be the “strongest driver that determines population growth” based on observations by Chip Taylor from Monarch Watch (Monarch Population Status, 04/2020 and 05/2020). In his May post, he also noted that the temperatures forecasted for June would be low, consequently impacting the “recolonization in the northernmost latitudes,” — that’s Ontario, which is exactly what we experienced.

Food is also another limiting factor. As the Monarchs are migrating south to Mexico, they need to feed on nectar to replenish their fat stores. Will they find it on their journey or in their summer breeding spot? What will the condition of the food be like and will it be safe? The trip south often takes these migrators through the US corn belt, where the prevalence of monocultures makes finding food particularly challenging. The use of neonicotinoids on these crops have also impacted the health of these insects. Increasing habitat around fields and reducing the use of pesticides would help to support Monarchs in this region.

monarch butterfly on butterfly weed

How Can We Help Monarchs?

So what can we do to help Monarchs? First and foremost, we can provide habitat. Like most butterflies and moths, Monarchs need two types of food plants: milkweed species for the caterpillars and suitable flowers with nectar for the adults. Monarchs will only lay their eggs on milkweed plants because their leaves are the only food the caterpillars will eat. The latex or ‘milk’ of these plants is potentially toxic to some animals, but Monarchs can metabolize the toxins which will ultimately make them distasteful if eaten. The adults will go to yellow-, pink-, and purple-hued flowers that they can land on, native species of plants being ideal since they support other local wildlife as well. There are ornamental species of plants that are also great nectar sources. The key is to have mixture of flowering plants available for the whole summer season, from late spring to fall, so that Monarchs arriving in the spring can find food, and the fall migrators can build up their fat stores for the journey south.

Finally, we wouldn’t know a lot of what we know about Monarchs if it wasn’t for citizen scientists — people like YOU. We have a better understanding of Monarch numbers thanks to people like you reporting when a Monarch (egg to adult) is observed on Journey North (North America) and Mission Monarch (Canada). Have you got some milkweed in your home garden? Have you seen it other places locally when you’ve gone for a walk? Carefully look under the leaves, by gently lifting the leaf tip and look for eggs and caterpillars. Do you see any crescent shaped holes in the leaves, or perhaps leaves that looked like they are tipping over. All of these are signs that a caterpillar may be around.

Learn More

Want to learn more? This Saturday, August 22 is National Flight of the Monarch Day. I’ll be in Hendrie Park between 11:00 a.m. and 1:00 p.m. at the Discovery Station to answer your questions and to record my Monarch sightings. I will have some caterpillars at various stages (or instars) for you to see, along with lots of information about how we ‘tag’ and track migrating butterflies. If you aren’t able to make it, but would like to learn more, we offer an interactive virtual program, Amazing Monarchs, suitable for learners of all ages. You are also welcome to contact me with any of your questions about Monarchs at kdavidsontaylor@rbg.ca.

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