"Being in Seattle, Washington, I can't conserve the birds I see and love just by taking action here," says Anna Lello-Smith, a researcher with the Wildlife Conservation Society (WCS), in a video call. "We think of birds as being ours, as North American, because they nest here. But in many cases, they spend most of the year in Central and South America. And that's the beauty of it: that birds connect us across hemispheres," she adds, referring to the results of a study she led that found that the Five Great Forests of Mesoamerica support between 10% and 46% of the global populations of 40 migratory bird species.
Although less well-known than their giant neighbor the Amazon rainforest, the Maya Forest (which covers parts of Mexico, Belize, and Guatemala), the Moskitia (in Honduras and Nicaragua), the Indio Maíz-Tortuguero conservation area (in Nicaragua and Costa Rica), the Amistad International Park (in Costa Rica and Panama), and the Darién (in Panama and northern Colombia) are remnants of the region's remaining rainforests and act as a protective corridor for numerous animal species. This is especially true for migratory birds that find refuge in these ecosystems, either to stay there during the North American winter or to make a stopover before reaching their final destination.
More than a third of all Kentucky warblers, for example, concentrate in these five large forests during the non-breeding season, as do a quarter of wood thrushes and golden-winged warblers, according to the research published in Biological Conservation.
"There are 'sister landscapes' across the continent," Lello-Smith asserts. Birds that in some months are found in forested areas of the Appalachians, the Mississippi Delta, the Great Lakes, New England, and around New York City -- or in Ontario and Quebec in Canada -- at other times inhabit Mesoamerica. And although this was already a known fact, due to the migration patterns themselves, the recent study managed to track the routes more precisely and on a larger scale.
To achieve this, they turned to eBird, a citizen science platform where local enthusiasts and experts upload information about the birds they have observed, including the species and the specific location where they saw it. The application already has more than two billion records contributed by over a million people, allowing scientists from WCS and Cornell University to track bird movements throughout the 52 weeks of 2022.
The researchers identified important dynamics. Some were almost intuitive, such as the fact that the Maya Forest -- the largest of the five, at 37,000 square kilometers -- had the highest average population percentage of all species. Meanwhile, Indio Maíz -- the smallest at 4,600 square kilometers -- had the lowest percentage. But there are other, more troubling findings. The latter, along with Moskitia, is among the areas most under pressure by deforestation, despite being the most important for migratory birds, supporting around 10% of the population of five species under some level of endangered status: the Kentucky warbler, the blue-winged warbler, the American thrush, the golden-winged warbler, and the cerulean warbler. Since 1970, North America has lost a total of 2.5 billion migratory birds of 419 species.
For Lello-Smith, the results are a call to action for organizations in the United States and North America to understand that they must also invest in conservation in other countries. This way, they can continue to see the birds that accompany them on their walks through Central Park in New York or that sing at dawn. "The Five Great Forests of Mesoamerica are disappearing due to illegal cattle ranching and fires," she points out. In the case of La Moskitia, a third of its vegetation has been cleared in just two decades.
As a parallel portrait of what is happening in the political and human context, the birds not only warn of the risk of losing the connection between north and south, but also of how organic it is to migrate across the continent.