As winter closes in across much of North America, migratory birds are heading south to warmer climes and more abundant food. But until recently, scientists didn't have a good understanding of exactly where they went.
Researchers from the Wildlife Conservation Society (WCS) and the Cornell Lab of Ornithology U.S. analyzed observations from eBird, a global citizen-science database of sightings submitted by bird-watchers. They found that in 2022 more than half of the 314 migratory bird species they studied went to the five great forests of Central America.
They write that 5 billion migratory birds funnel through Central America each year. Many stop in the rainforests, alpine wetlands and mangroves of the five great forests: Selva Maya in Mexico, Belize and Guatemala; Moskitia in Honduras and Nicaragua; Indio Maíz-Tortuguero in Nicaragua and Costa Rica; La Amistad in Costa Rica and Panama; and the Darién in Panama and northern Colombia. Collectively, these forests cover more than 10 million hectares (2.5 million acres), the researchers write.
The five great forests. Image courtesy of Trillion Trees.
The study found that many species spend the entire winter in these forests, including one in four wood thrushes (Hylocichla mustelina). Others, including one-third of broad-winged hawks (Buteo platypterus) and 40% of cerulean warblers (Setophaga cerulea) use the forests as a stopover for journeys farther south. Cerulean warbler populations have declined by roughly 70% since the 1970s.
"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," study co-author Viviana Ruiz Gutierrez, director of conservation science at the Cornell Lab of Ornithology, said in a statement.
The five great forests, crucial for both migrating birds and permanent residents like jaguars, tapirs and monkeys, are increasingly under pressure from illegal deforestation, lead author Anna Lello-Smith, a conservation scientist at WCS, told Mongabay in a video call.
The two northernmost forests, Selva Maya and Moskitia, have lost roughly a quarter of their area in the last 15 years. "They were the most important for migratory birds in terms of the percent of populations that they're supporting, but those are also some of the most threatened by illegal cattle ranching and fire," Lello-Smith said.
While the migratory birds are concentrated in the five forests over winter, the study found that during the breeding season, they spread across the eastern U.S. and Canada. There, they face threats from additional habitat loss and degradation, house cats, vehicle collisions and pollution.
Lello-Smith said she hopes this research will foster more stewardship connections between the Central America and North America.
"These birds are really connecting people and communities between these distant landscapes, and we all have this shared responsibility to protect their habitats throughout their range and to work together to figure out solutions," she said.
Banner image: A cerulean warbler. Image by DiaGraphic via Wikimedia Commons (CC BY 2.0).