Kentucky warblers depend on Mexican rainforests thousands of miles away

The connection between a Kentucky woodland and the Selva Maya rainforest in southern Mexico isn't poetic metaphor—it's ornithology. When a Kentucky warbler sings in Appalachia, half its species is wintering in Central American forests that are disappearing.

Scientists at Cornell University and the Wildlife Conservation Society used billions of amateur bird sightings from eBird—a crowdsourced database of bird observations—to map something most North Americans never consider: the forests they're trying to save at home depend entirely on forests they've never heard of abroad.

The data is stark. At least 163 migratory bird species pass through or stay in just five key Central American forests. Forty of those species have at least 10% of their global population in these forests for at least one week each year. For 16 species, the proportion jumps to 20% or more. The Kentucky warbler, a tiny lemon-yellow songbird that defines eastern North American forests, has nearly half its entire population—46%—concentrated in the Selva Maya during winter months. The cerulean warbler, named for its deep blue plumage, sends almost a third of its global population through the Moskitia region of Honduras in early April.

Both species are declining, as are the forests they depend on.

Why This Matters Across Borders

The research, published last week in Biological Conservation, reframes deforestation in Central America as a North American problem. "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, an ecologist with the Wildlife Conservation Society's Mesoamerica program.

The scientists chose this angle deliberately. By tracing individual species across thousands of kilometers, they're trying to shift how people in wealthy, politically powerful North America think about forest loss in their southern neighbors. It's not abstract data about hectares disappearing. It's the bird you might hear on a spring morning in Kentucky—and the specific rainforest it can't survive without.

"Every fall, billions of birds pour south through the narrow land bridge of Central America," said Viviana Ruiz Gutierrez, director of Conservation Science at Cornell's ornithology lab. "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."

The hope is that naming these connections—what researchers call "sister landscapes"—will help build conservation efforts that cross political boundaries. That means directing resources and expertise from North America to boost local protection efforts, creating a shared stake in keeping these forests intact. You can't save Kentucky's birds without saving Mexico's rainforests. The two are already inseparable.