Monarch butterfly populations in North America have been in dramatic decline for several decades. But in a glimmer of hope for the iconic orange-and-black species, the 2025 population estimate was roughly 64% higher compared to the previous year.
Scientists split migratory monarchs (Danaus plexippus) into two populations — western and eastern — depending on which side of the Rocky Mountains they fall on. Both are considered endangered on the IUCN Red List but neither have been formally listed on the U.S. endangered species list. Eastern monarchs have declined by 80% since the 1980s, and the western population by more than 95%, edging them toward extinction. Nonmigratory populations, found throughout the neotropics, aren’t considered endangered.
The entire population of eastern monarchs overwinter in the oyamel fir (Abies religiosa) forests of central Mexico. Researchers estimate their population based on how much forest the butterflies occupy. Over the winter of 2024-2025, monarchs covered just 1.79 hectares (4.42 acres); a year later, it was 2.93 hectares (7.24 acres).
That works out to more than 61 million monarchs, says Wendy Caldwell, executive director of the monarch butterfly conservation nonprofit Monarch Joint Venture. “It is variable; however, 21 million monarchs per hectare is a generally accepted estimate in the current literature,” she told Mongabay by email.
It can take four generations of monarchs to complete the migration journey from Mexico to Canada or the northern United States and back.
Much work has gone into protecting the monarch’s winter habitat in Mexico. “One of the greatest achievements of this work is that illegal logging in the core zone of the Monarch Butterfly Biosphere Reserve has been virtually eradicated since 2008,” María José Villanueva, director of WWF Mexico, told The Guardian. “This means that the forests that represent the fundamental habitat for the monarch butterfly’s hibernation are being protected and conserved.”
While the 2025 population increase for eastern monarchs is a positive sign, conservation challenges remain. Scientists estimate that for long-term survival, eastern monarchs should inhabit at least 6 hectares (15 acres) of oyamel fir forest, which has happened just once in the last decade.
Caldwell said many factors have contributed to monarch declines, including “long-term habitat loss, especially milkweed and nectar plants, along with pressures from climate change, extreme weather, and other human-induced stressors and natural enemies.”
She expressed cautious optimism that the new population data is good news, but said monarch conservation is an ongoing challenge. “To support long-term recovery, we need not only large-scale habitat restoration but also more distributed and abundant habitat across all land use types, from backyards to large tracts of public land, along with stronger integration of habitat into working lands. These actions are underway across many sectors, but continued expansion and coordination are needed to reach a more stable population level.”
Banner image: Monarch butterflies overwintering in Mexico. Image by Scott Clark via Wikimedia Commons (CC BY 2.0).
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