Scientists estimate that 6 hectares, which is about 15 acres (1 hectare = 2.47 acres) is the extinction threshold for the migratory butterflies’ survival in North America. The latest count, conducted in 2023-2024 by World Wildlife Fund Mexico, found that overwintering monarchs are occupying 0.90 hectares or 2.2 acres. This was a 59.3% decrease from the previous season which was 2.22 hectares or 5.5 acres.

This decline is considered a benchmark for the species’ overall abundance and is attributed to climatic variations in breeding areas in Canada and the United States, resulting in reduced milkweed abundance due to high temperatures and drought, alongside land-use changes and herbicide use impacting essential nectar plants for adult monarchs. This is the second-lowest number counted to date. The lowest was 0.67 hectares during the 2013-2014 overwintering season.

The annual monarch migration and multi-generational cycle rely on well-timed and abundant resources to sustain and grow the population. Any weak or broken link in this cycle can cause the monarch population to struggle.