Space for Milkweed and Monarchs

Sault Ste. Marie Canal National Historic Site

By Courtney Irvine

The large size, vibrant orange colour and well-known long distance migration of Monarch butterflies has made them an iconic Canadian species. However, the Monarch is currently in peril due to a loss of habitat. Parks Canada is helping Monarch butterfly conservation by protecting milkweed at our sites.

Protection of habitat is critical if Monarchs are to survive. This species is listed as “endangered” by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) because of habitat loss. Monarch butterflies need milkweed plants to complete their lifecycle – eggs are laid on milkweed and caterpillars feed on this plant until forming a chrysalis and transforming into a Monarch butterfly. The increasing use of herbicides and subsequent decline of milkweed is a substantial threat to the Monarch butterfly in its North American range.

In 2017, Parks Canada staff conducted surveys at Fort St. Joseph and Sault Ste. Marie Canal National Historic Sites to determine where milkweed was present.  Monarch caterpillars and butterflies were observed during these surveys, confirming these locations are used as breeding habitat for the species.

A Monarch caterpillar on milkweed at Fort St. Joseph National Historic Site

Next, we developed a Best Management Practice for vegetation maintenance to ensure routine mowing and trimming did not endanger the persistence of milkweed plants and their Monarch counterparts at these sites.  We identified areas where vegetation maintenance could be eliminated altogether to promote milkweed and wildflower growth. A window of time was also identified when mowing and trimming should not be completed in low visitor-use areas to protect milkweed and Monarchs from disturbance during breeding. In areas that require continuous maintenance (for example, along roadsides and in high visitor-use zones such as picnic areas), staff perform vegetation maintenance early in the spring and often throughout the summer to prevent the growth of milkweed entirely. That way, no Monarch eggs or caterpillars can be destroyed by vegetation maintenance. No herbicides or insecticides are used for vegetation management at either of the sites.

We hope Parks Canada’s Best Management Practice for vegetation maintenance at Fort St. Joseph National Historic Site and Sault Ste. Marie Canal National Historic Site helps foster the persistence of Monarch butterflies in Canada. This summer you may notice new areas at these sites where milkweed and wildflower establishment are promoted. Keep your eyes peeled for Monarch eggs, caterpillars and butterflies making use of this new habitat!

In my role as Impact Assessment Officer for the Northern Ontario Field Unit, I assist with initiatives such as this to ensure our sites protect Canada’s natural and cultural heritage while maintaining visitor use and enjoyment. Send me an email if you have an idea about how we can do more?

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