Blazing trails for monarch butterfly habitat in urban areas with nature-based solutions

As pollinating insects, butterflies are critical to the health of our ecosystem. They ensure the reproductive success of plants, crops and the survival of the wildlife that depend on those plants for food and shelter. However, climate change and urbanization are causing monarch butterfly habitat loss, accelerating their population decline.

Along the shores of Lake Ontario in Toronto, the monarch butterflies make a brief stop while migrating south for the winter during a two-month window between August and October. Failing to restore the depleted migratory habitats in time for the short re-fueling window for the butterflies on their 5000 km migration corridor could further impact the population.

As Canada’s fastest-growing city, Toronto and the surrounding area has experienced an increased demand for residential development. A project was proposed in a location intersecting with the butterfly migration path. The developer wanted to ensure that the critical residential development would not negatively impact the monarch butterfly population. As a condition of the draft plan of subdivision approval, an environmental impact assessment was completed.

A solution was needed that would facilitate the permitting approval of the residential development while ensuring the availability of the habitat in time for the butterflies’ migration and throughout the construction period.  

Our Natural Resources team set out three objectives for restoring the monarch butterfly migratory habitat over a 45-acre area:

1. Evaluate the impact of the development on monarch butterfly habitat quality in the GTA.
2. Explore the effectiveness of vegetative matting as a nature-based solution for habitat restoration.
3. Emphasize interdisciplinary collaboration to address the challenges posed to ecosystems by urbanization.
   
   

We surveyed the study area over the full fall migration period to determine the significance of the habitat to monarch butterflies within the migratory corridor. We assessed potential disturbances resulting from the proposed residential development. We also documented opportunities to retain habitat and compensation options.

The surveys began in 2016 and have been ongoing during an eight-year period to obtain the necessary approvals. Permits were issued in spring of 2024, with construction commencing immediately. The vegetative matting solution was implemented to salvage existing prime nectaring habitats, stabilize slopes, and quickly revegetate disturbed areas. Now that the revegetation is complete, we will monitor the vegetation establishment, soil stability, and butterfly presence over six years, totaling 14 years since initiating the project.

The developer obtained construction approvals after providing evidence that monarch butterflies and their habitat can be maintained on-site. The vegetative matting technique provides rapid soil stabilization and increased shear strength, with immediate nectaring habitat for monarch butterflies within this urban setting.

In addition to preserving biodiversity and ensuring the protection of this species-at-risk, once a year, GTA residents will enjoy the beauty of the butterflies’ orange-filled spectacle when they make their way through the migratory corridor.

Nature-based solutions in urban habitat restoration have great potential. They require collaboration efforts among ecologists, engineers, policymakers and owners for effective conservation. The use of innovative, nature-based techniques help enhance urban biodiversity and support imperiled species like the globe-trotting monarch butterfly.