Monarch Butterfly (Danaus plexippus) in Halton

Halton’s meadows, ravines, and backyard gardens sit along one of North America’s great wildlife highways: the migratory path of the eastern Monarch Butterfly. Each spring and fall, these striking orange‑and‑black travellers pause here to breed, refuel on nectar, and rest before continuing a 4,000‑kilometre journey between central Mexico and the Great Lakes. But today the Monarch’s future is uncertain—the species is officially Endangered in Canada, its numbers have plummeted, and the habitats it depends on are disappearing. This page explains why Monarchs matter to Halton, what threats they face, and how every resident can help restore their flight.

Meet the Monarch

Lifecycle in a nutshell: From egg to caterpillar to chrysalis to adult, every Monarch generation begins on milkweed. The caterpillars feed exclusively on milkweed leaves, storing cardiac glycosides that make them unpalatable to predators.
Epic migration: The butterflies we see in Halton are part of the eastern population. The super‑generation that emerges in late summer will fly south through the Niagara‑Hamilton corridor, funneling along Lake Ontario’s north shore before crossing the continent to overwinter in Mexico’s oyamel fir forests.
Pollination partner: While adult Monarchs aren’t specialized pollinators, their constant nectaring on goldenrods, asters, and native sunflowers helps sustain late‑season blooms and supports a broader web of pollinators.

A Species in Crisis

Endangered status: In December 2023, the Government of Canada uplisted the Monarch to Endangered under the federal Species at Risk Act (SARA) following an 84 % population decline since the mid‑1990s.
Shrinking winter colonies: The area occupied by overwintering colonies in Mexico dropped from more than 18 hectares in 1996 to just 1.79 hectares in winter 2024‑25.
Key threats: Habitat loss (especially milkweed eradication), pesticides such as neonicotinoids, climate‑driven extreme weather, and urban development all contribute to the decline.

Monarchs in Halton Today

Seasonal timings: First adults usually arrive in late May or early June; peak southbound migration passes through from late August to mid‑September, often staging along Burlington’s lakefront parks, Bronte Creek Provincial Park, and the Niagara Escarpment.
Local initiatives: Community groups like Oakvillegreen’s Milkweed Challenge and the Monarch Awards run by Halton Region Master Gardeners are restoring habitat and celebrating pollinator‑friendly gardens.
Citizen science: Residents log sightings on iNaturalist and Journey North, providing crucial data that guides conservation priorities.

How You Can Help

Grow milkweed – Plant Common (Asclepias syriaca), Swamp (A. incarnata), and Butterfly (A. tuberosa) milkweeds.
Add late‑season nectar – Goldenrods, asters, Joe‑pye‑weed, and native sunflowers fuel the southbound flight.
Skip the chemicals – Avoid insecticides and herbicides in gardens and on lawns.
Record your observations – Submit Monarch and milkweed sightings to citizen‑science platforms.
Protect local natural areas – Support policies and projects that conserve meadows, hedgerows, and shoreline habitat.

By the Numbers

84 %

Decline in the eastern Monarch population since 1993

1.79 ha

Area of overwintering colonies in Mexico in winter 2024‑25

200

Milkweed plants targeted for planting in Oakville Green’s 2025 Halton Milkweed Challenge