Sipping a collective 400 million cups a day, most coffee-loving Americans are likely unaware of how their cherished brew impacts tropical bird populations in some of the world’s most critical biodiversity hotspots.Fortunately, University of Utah biologist Çağan Şekercioğlu and his team of researchers are on it.Their landmark 12-year study of 57,255 individually banded birds representing 265 species at 19 Costa Rican sites sheds new light on how tropical birds, a key indicator of ecosystem health, are faring across a patchwork of habitats in a changing agricultural countryside. The team compared bird populations on primarily open coffee farms (with small amounts of shade) with those in remaining forested areas. Published Monday in the Proceedings of the National Academy of Sciences and partially funded by the National Geographic Society, the study reveals that even a small increase in coffee farm tree cover, from 7 to 13 percent to be exact, can provide a significant boost to birds.Tropical agriculture is a major driver of species loss. Researchers found that coffee farms offering some tree shade (not to be confused with coffee that is “shade grown” under a full canopy of mature trees) are still experiencing species decline and are no substitute for large swaths of protected forest. Across coffee farms and all sizes and types of forest, researchers found 61 percent more bird species’ populations declined as grew or remained steady. The sole exception to this trend was the 1,500-square mile La Amistad International Park, a transboundary area nearly the size of Rhode Island spanning Costa Rica and Panama.Why does this matter?“Bird diversity is a very good indicator of the overall environmental health of the system. That’s why I think people should be concerned about a study like this,” says Robert Rice, a geographer at the Smithsonian Migratory Bird Center for conservation research and public education, who wasn’t involved in the study.