"Monarch population" refers to the number of monarch butterflies that exist in a specific area or region. It is a measure of how many monarch butterflies there are in a particular group or population. Full definition
More generally, the strategy sets a number of goals: cutting overwintering bee colony losses to 15 % (from roughly 30 % in recent years) by 2025, restoring nearly 3 million hectares of land for pollinators in 5 years, and boosting monarch populations in a key wintering area in Mexico to 225 million by 2020 (roughly four times as high as now). (sciencemag.org)
In that way, the migration is vital to keeping OE under control in the North American monarch population, Satterfield explains. (sciencemag.org)
So the best way to help declining monarch populations — and to preserve their epic, multi-generational migration — is to plant milkweed. (scientificamerican.com)