Introduction: The Great Migration and a Missing Piece of the Puzzle
As autumn paints North America’s landscapes in hues of red and gold, a silent exodus begins. Millions of migratory birds—from tiny warblers weighing no more than a coin to majestic hawks with wingspans of over a meter—abandon their breeding grounds in the United States and Canada, embarking on thousands of kilometers of perilous journey south. Driven by the need to escape frigid winters and scarce food supplies, these avian travelers seek warmer climes and abundant resources to survive until spring. For decades, however, scientists have faced a critical knowledge gap: while the northern breeding grounds of these birds were well-documented, their exact wintering destinations and the specific habitats they relied on remained largely a mystery. This gap hindered effective conservation efforts, as protecting a species requires safeguarding its entire life cycle—from nesting sites to winter refuges. A groundbreaking study by researchers from the Wildlife Conservation Society (WCS) and the Cornell Lab of Ornithology has now filled this void, revealing that Central America’s five great forests are not just waypoints, but vital lifelines for over half of North America’s migratory bird species.
Research Methods: Harnessing Citizen Science to Unlock Migration Secrets
The study, published in 2025, leveraged the power of citizen science—specifically data from eBird, a global database launched by the Cornell Lab of Ornithology in 2002. eBird aggregates observations from millions of birdwatchers worldwide, who submit real-time records of bird sightings, including species, location, and date. This crowdsourced data has transformed ornithology, providing researchers with an unprecedented wealth of information across vast geographic scales and long timeframes. For this research, the team analyzed eBird observations from 2022, focusing on 314 migratory bird species that breed in North America and migrate south for the winter. By mapping the concentration of these species during the non-breeding season, the researchers identified a clear pattern: more than 50% of the studied species converged on five contiguous forest complexes in Central America. The study also estimated that an astonishing 5 billion migratory birds pass through Central America annually, with the five forests acting as primary destinations or critical stopover sites. “Citizen science has given us a bird’s-eye view of migration that was once impossible,” said Viviana Ruiz Gutierrez, co-author of the study and director of conservation science at the Cornell Lab of Ornithology. “Every birdwatcher’s checklist is a piece of the puzzle that helps us protect these incredible travelers.”
The Five Great Forests: Central America’s Ecological Crown Jewels
The five forests identified in the study form a network of biodiversity hotspots spanning seven countries, covering over 10 million hectares (24.7 million acres)—an area roughly the size of Costa Rica. Each forest boasts unique ecological features, collectively supporting a mosaic of habitats including tropical rainforests, cloud forests, alpine wetlands, mangroves, and riparian corridors. Selva Maya, the northernmost of the five, stretches across southern Mexico, Belize, and Guatemala, and is one of the largest intact tropical forests in the Americas, characterized by dense canopy cover and abundant water sources. To the south, Moskitia spans Honduras and Nicaragua, a remote region of swamps, rivers, and lowland forests that provides critical wetland habitats for waterbirds and waders. Indio Maíz-Tortuguero, straddling Nicaragua and Costa Rica, includes coastal mangroves and tropical dry forests, serving as a bridge between northern and southern migration routes. La Amistad, shared by Costa Rica and Panama, rises into mountainous terrain, offering cool, misty cloud forests that support species adapted to higher elevations. Finally, the Darién connects Panama to northern Colombia, a rugged, biodiversity-rich region that acts as the gateway between Central and South America, with intact rainforests that shelter both migratory birds and iconic resident species like jaguars, tapirs, and howler monkeys. Together, these forests function as a single interconnected system, providing food, water, and shelter for migratory birds at every stage of their winter journey.
Birds’ Dual Dependence: Winter Refuges and Stopover Havens
The study uncovered two key ways migratory birds rely on the five great forests: as long-term wintering grounds and as essential stopover sites. For many species, these forests are not just temporary rest stops but permanent winter homes. Among them is the wood thrush (Hylocichla mustelina), a beloved songbird with a haunting melody—one in four individuals of this species spends the entire winter in the five forests, foraging on insects and berries to rebuild energy reserves for the spring migration north. For other birds, the forests serve as critical “pit stops” where they refuel before continuing their journey to South America. This includes the broad-winged hawk (Buteo platypterus), a raptor that migrates in large flocks called “kettles”—one-third of these hawks pause in the forests to hunt small mammals and reptiles, doubling their body weight to sustain the final leg of their migration. Perhaps most notably, the cerulean warbler (Setophaga cerulea), a tiny blue-and-white songbird whose population has plummeted by 70% since the 1970s, depends heavily on the five forests: 40% of the remaining individuals use them as stopover sites, making these habitats a lifeline for the species’ survival. “The density of migratory birds in these forests is staggering,” Gutierrez noted. “A single hectare can support hundreds of warblers, flycatchers, and vireos, meaning every patch of forest protected here has an outsized impact on global bird populations.”
The Looming Crisis: Threats to Central America’s Vital Forests
Despite their ecological importance, the five great forests are under escalating pressure from human activities, putting both migratory birds and resident species at risk. Lead author Anna Lello-Smith, a conservation scientist at WCS, emphasized that the two northernmost forests—Selva Maya and Moskitia—are facing the most severe threats. Over the past 15 years, these forests have lost roughly a quarter of their original area, primarily due to illegal deforestation driven by cattle ranching, agricultural expansion, and logging. In Selva Maya, for example, illegal ranchers clear vast swaths of forest to create pasture for cattle, a practice fueled by high demand for beef in regional and international markets. Moskitia, meanwhile, is plagued by uncontrolled wildfires, many of which are set intentionally to clear land for farming, as well as illegal logging of valuable hardwoods like mahogany. The other three forests—Indio Maíz-Tortuguero, La Amistad, and the Darién—face similar pressures, albeit to a lesser extent, including habitat fragmentation from roads, mining activities, and the expansion of palm oil plantations. Compounding these threats is climate change, which is altering rainfall patterns and increasing the frequency of extreme weather events, further degrading forest habitats and reducing the availability of food for migratory birds. “These forests are a conservation priority not just for Central America, but for the entire Western Hemisphere,” Lello-Smith warned. “If we lose them, we risk losing hundreds of migratory bird species that depend on them.”
Double Jeopardy: Migratory Birds’ Fight for Survival Across Borders
The challenges facing migratory birds extend far beyond their wintering grounds—they face a “double jeopardy” of threats in both their breeding and migration habitats. During the summer breeding season, which takes place across the eastern United States and Canada, the birds contend with habitat loss from urbanization and agricultural development, as forests are cleared for housing, highways, and cropland. Domestic cats—both owned and feral—are another major threat, killing an estimated 2.4 billion birds annually in the United States alone. Vehicle collisions, pollution from pesticides (which reduce insect populations, a key food source for many birds), and climate change-induced shifts in breeding seasons also take a heavy toll. For species like the cerulean warbler, which already faces steep population declines, the combination of threats in breeding grounds and wintering habitats creates a perfect storm. A bird that survives the perils of migration to reach Central America may find its winter refuge destroyed by deforestation, while a bird that successfully winters may return north to find its nesting site paved over. This cross-border threat landscape underscores the need for coordinated conservation efforts that span multiple countries and ecosystems.
A Call for Cross-Border Stewardship: Uniting Nations to Protect Migratory Birds
The study’s findings highlight a critical truth: migratory birds do not recognize national borders, and their conservation cannot be achieved in isolation. Lello-Smith emphasized that the research offers a unique opportunity to foster stewardship connections between North America and Central America. “These birds are biological ambassadors, linking communities in Canada, the U.S., and Central America through their annual journey,” she said. “We all share a responsibility to protect their habitats, whether they are nesting in a backyard in Ohio or wintering in a forest in Guatemala.” This cross-border collaboration could take many forms: conservation organizations in North America could partner with local communities in Central America to support sustainable land-use practices, such as agroforestry (which combines trees with crops to provide habitat and income for farmers). Governments could work together to establish protected areas and wildlife corridors that span national boundaries, ensuring birds have safe passage during migration. Citizen scientists could also play a role, with birdwatchers in North America contributing data to track migratory patterns and support conservation initiatives in Central America. Additionally, raising public awareness about the link between North American backyards and Central American forests could inspire individuals to take action—from reducing pesticide use to supporting conservation organizations working across borders.
Conclusion: Protecting Forests, Protecting a Hemispheric Heritage
The study by WCS and the Cornell Lab of Ornithology has shed light on one of nature’s most remarkable journeys, revealing the vital role of Central America’s five great forests in sustaining North America’s migratory birds. These forests are more than just patches of green—they are critical lifelines that support billions of birds annually, providing food, shelter, and safe passage during their epic migration. Yet, as these forests face unprecedented threats from deforestation, climate change, and human activity, the future of migratory birds hangs in the balance. The solution lies in recognizing that conservation is a shared responsibility, one that transcends national borders and unites communities across the Americas. By protecting Central America’s great forests, we are not just saving birds—we are preserving a hemispheric heritage, a natural wonder that connects us all. As winter migratory birds continue to arrive in these forests each year, they serve as a reminder of our interconnectedness with nature and the urgent need to act together to protect the habitats that sustain us all.
