Scientists estimate that the extinction threshold for migratory monarch butterflies in North America is 6 hectares (about 15 acres). The latest count by World Wildlife Fund Mexico in 2023-2024 found that overwintering monarchs occupy only 0.90 hectares (2.2 acres), a 59.3% decrease from the previous season’s 2.22 hectares (5.5 acres).

This decline is attributed to climatic variations in breeding areas, resulting in reduced milkweed abundance due to high temperatures and drought, alongside land-use changes and herbicide use impacting essential nectar plants. The annual monarch migration and multi-generational cycle rely on well-timed and abundant resources to sustain and grow the population. Any disruption in this cycle can cause the monarch population to struggle.