A summer-long Mission for Monarchs

Fort St. Joseph National Historic Site

By Jeralyn and Michael Bohms

Fort St. Joseph National Historic Site has embarked on a multi-year project to enhance the site’s meadow habitat for monarchs and other pollinators. In 2022, staff spent the summer monitoring milkweed to find out just how many monarchs are using the meadow around the fort’s ruins.

In 2018, the Government of Canada launched an inter-departmental initiative, called Canada’s Nature Legacyaimed at protecting the country’s biodiversity, ecosystems, and natural landscapes. Fort St. Joseph is participating by enhancing habitat for the monarch butterfly and other essential pollinators. The meadow landscape around the ruins of the fort provides critical habitat for monarchs at the northern edge of their range. The meadow includes milkweed plants for monarch caterpillars and native wildflowers for adult butterflies.

Declining monarch populations across North America are raising alarm bells in the scientific community, prompting the Canadian government to list the monarch as a Species of Special Concern. Habitat loss is a key factor in this population decline, which makes places like the meadow around the ruins of Fort St. Joseph critical to the species’ reproduction and survival.

Since there is limited scientific data on exactly how monarchs have been using the meadow, this past summer Fort staff went on an extended monarch mission. Using methods established by Montreal’s “Éspace pour la vie Insectarium” and the Mission Monarch Expert program, staff counted monarchs. Three survey plots were established in the meadow, each about one hectare (100m by 100m). Every two weeks, from mid-May through late September, staff members walked through each plot looking for milkweed plants. The milkweed plants were carefully inspected to search for the miniscule greenish-white eggs of monarchs, and, as they hatched, the unmistakable yellow, black, and white striped caterpillars. During each plot’s survey, 100 milkweed plants were inspected each time, and the data recorded.

Staff also looked for adult monarch butterflies in each of the three plots. Designated routes were established and monitored on days when it was warm, but not too hot and not too windy. Adult monarchs were counted, and their activity documented, including what flowers they were feeding on or if they were seen laying eggs.

Through this study, staff documented the first arrival of adult monarchs in late May and found eggs on milkweed by early June. In August, a caterpillar was observed making its chrysalis and about 2 weeks later, hatching into a beautiful adult butterfly! The last monarchs headed south in mid-September, leaving the meadow to begin the long journey to central Mexico. Throughout the summer there were typically about 8-12 monarch butterflies spotted during each survey, while at peak migration in early September, 52 monarchs were seen in one hour!

This data will help quantify the effect of the work we are doing to maintain and enhance the meadow around the fort. We will continue to document the presence of monarchs, as well as the milkweed and other wildflower nectar sources in the environment, to gauge the success of the project. Visitors to Fort St. Joseph are welcome to join us in this effort! Learn more about citizen science opportunities with Mission Monarch and iNaturalist from our friendly staff at the Visitor Centre.


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