Every year, the Western monarch butterfly population undertakes an epic migration that spans 11 states in the region. About half that acreage is public land, but a new analysis has found that the migrating insects greatly prefer private property, suggesting that private-land conservation has outsized importance for the species’ continued survival.
A study published in the journal Frontiers in Ecology and Evolutionon Nov. 20 found that federally managed land makes up 11.7% of the butterflies’ spring migration range and 23.5% of their fall migration range, with state, local and non-governmental organizations managing a total of about 4% of each season’s range. (Tribal land boundaries were not included in the database used for the analysis.)
This study is the first analysis of land ownership within the butterfly’s Western migration corridor, said lead author Bruce Young. “To protect the monarch, we can’t just depend on the federal government,” said Young, chief scientist at NatureServe, a nonprofit that collects and maps biodiversity data throughout North America. Emma Pelton, a senior conservation biologist at the Xerces Society for Invertebrate Conservation, emphasized that more collaboration is needed. “It hits home the point that we really need both public and private partnerships in modern conservation,” she said.
“To protect the monarch, we can’t just depend on the federal government.”
The monarch butterfly has lost 90% or more of its population in the West since the 1980s. The Eastern monarch butterfly, a distinct population that migrates between central Mexico and southern Canada, is more numerous but is also declining.
Much of the Western population winters on the California coast, where most of their habitat has been lost to development. The monarch’s migratory habitat is threatened as well: Herbicide use has reduced the amount of milkweed available to feed larvae during the spring and early summer, while extreme weather has altered the blooming times of flowering plants, disrupting the nectar supplies that adult butterflies need for energy.
This fall, counts conducted by the Xerces Society reported 7,000 monarchs in the entire Western population, the second-lowest number recorded for this time of year since the late 1990s. While peak winter season counts are expected to be slightly higher, Pelton is still concerned. A decision on Endangered Species Act protection for the species is expected in early December.
Researchers have already mapped the butterfly’s overwintering sites, which are mostly concentrated along the California coast. This new study was requested by the Bureau of Land Management, which asked NatureServe to assess the monarch’s land use in the West throughout the year. “We have to look at all different parts of the life cycle to figure out where we can help conserve this iconic species,” Young said.
Migrating monarchs’ apparent preference for private land may be due to the fact that over a century ago, when settlers displaced Indigenous people and claimed property across the region, Western river valleys and other productive agricultural lands often ended up in private hands. Arid, densely forested or higher-elevation landscapes are more likely to be managed by the Bureau of Land Management or Forest Service. But since migrating monarchs need to eat and feed their larvae, they often gravitate toward fertile ground with lots of plants.
The new study and others like it would be impossible without the work of citizen scientists — people who see a monarch in the backyard, snap a picture and post it on a platform such as Journey North. Researchers used thousands of observations collected between 2010 and 2021 to model where the butterflies go. The results surprised Young, who had assumed that migrating monarchs spent more time on federal and state lands.
Incentivizing private landowners to manage their land for other species’ benefit is always important, Young said, particularly if that land lies along the banks of rivers, streams and lakes where nectar plants grow. Careful use and timing of pesticides in agricultural areas matters, too, especially along the migration route through California’s Central Valley to the coast. Planting a variety of native plants, including milkweed, is another way to help the struggling insect. It may become even more crucial under President-elect Donald Trump, whose administration is expected to boost fossil fuel production on public land and roll back environmental protections.
Fortunately, the creation of a national pollinator health strategy and task force in 2015 has helped government agencies expand their capacity for pollinator protection, Pelton said. Today there are more pollinator-specific federal positions than ever before, and insect protection has become a priority for many managers. “Hopefully, that continues,” she said.
