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Ithaca, NY—Every spring, the familiar songs of Wood Thrushes and warblers return to the parks and backyards of eastern North America. But their journey begins far to the south—in the lush, remote forests of Central America that sustain them throughout most of the year.
A new study from the Wildlife Conservation Society (WCS) and the Cornell Lab of Ornithology (Cornell Lab), published in Biological Conservation , reveals that the Five Great Forests of Central America—which stretch from southern Mexico to northern Colombia—are indispensable lifelines for dozens of migratory bird species that link the Americas.
Using information on where bird populations concentrate week by week each year—made possible by millions of observations around the world from birdwatchers on the Cornell Lab's eBird platform—scientists found that these five forests collectively support between one-tenth and nearly one-half of the global populations of 40 migratory bird species, including some of North America's most rapidly declining birds.
"What happens in Central America directly affects the birds we love in the United States and Canada," said Anna Lello-Smith, lead author and conservation scientist at WCS. "These forests aren't just tropical wilderness—they're at the heart of migration, sustaining many of our birds for more than half the year. They provide the food and shelter that allow Wood Thrushes, Magnolia Warblers, and so many others to return north to fill our spring with song and color."
Among the study's most striking findings:
- More than one-third of the world's Kentucky Warblers and nearly one-quarter of all Wood Thrushes and Golden-winged Warblers spend the winter within these forests.
- Over 40 percent of the global Cerulean Warbler population, a species that has declined by more than 70 percent since 1970, funnels through these forests during spring migration.
- The Selva Maya (spanning Mexico, Belize, and Guatemala) and the Moskitia (in Honduras and Nicaragua) are the most critical forests for these birds—yet also the most threatened, having lost a quarter of their area in just 15 years, primarily to illegal cattle ranching.
Together, the Selva Maya, Moskitia, Indio Maíz-Tortuguero, La Amistad, and Darién form a living bridge the size of Virginia—home not only to migratory songbirds but to jaguars, scarlet macaws, and tapirs. For birds that migrate thousands of miles each year, these forests are irreplaceable rest stops and winter refuges.
"Every fall, billions of birds pour south through the narrow land bridge of Central America," said Viviana Ruiz-Gutierrez, director of Conservation Science at the Cornell Lab of Ornithology and co-author of the study. "The density of migratory warblers, flycatchers, and vireos crowded into these five forests is astounding, and means that each hectare protected there safeguards a disproportionate number of birds."
But these forests are vanishing. Deforestation, fueled largely by illegal cattle ranching, has already consumed millions of acres. In the Moskitia alone, nearly one-third of the forest has been cleared in just two decades.
"If we lose the last great forests of Central America—and we are—we lose the birds that define our eastern forests in North America," said Jeremy Radachowsky, Regional Director for WCS's Mesoamerica Program. "But by supporting rural communities, governments, and conservation partners on the ground, we can still turn the tide."
Across the region, Indigenous and local communities are leading efforts to restore degraded land, fight forest fires, and revive bird-friendly livelihoods such as sustainable cacao and allspice production. They frequently put their lives on the line to protect these vital habitats for birds, but they can't do it alone.
"Imagine the possibility of linking with those efforts," said Ruiz-Gutierrez, "so that we can work together across the Americas to bring back our shared migratory birds."
In the past, joint conservation efforts across borders have been limited by a lack of understanding of how birds connect habitats and people across seasons. To guide international collaboration, the study applied a framework developed by Partners in Flight and the Cornell Lab to trace "stewardship connections"—regions of North America where species that depend on the Five Great Forests concentrate to breed
The Five Great Forests are tightly linked to forested areas of the Appalachians, the Mississippi Delta, the Great Lakes, New England, and around New York City, forming what researchers call "sister landscapes": places connected by the same bird species at different times of year.
In essence, the Five Great Forests are the mirror of North America's eastern forests—tropical counterparts that shelter the same community of forest-loving migratory birds, from Scarlet Tanagers and Kentucky Warblers to Golden-winged Warblers and Broad-winged Hawks, during the months they spend far from their breeding grounds. Protecting and restoring these vital migratory stopovers and wintering habitats is key to ensuring that eastern forest birds keep coming back to North America.
"Every hectare we protect in Central America has ripple effects for birds and people across the hemisphere," said Lello-Smith. "The forests that sustain thrushes and warblers also support communities. If you love watching your birds come back each spring, we invite you to discover the tropical forests they call home for most of the year—and help protect them."
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