Scientists studying data collected over more than three decades found accelerating losses. Their research offers clues about the causes.

Birds in the United States are not only declining, but they are declining faster, especially in areas with intensive agriculture, according to new research. Overall drops in bird population, measured from 1987 to 2021, were sharpest in warm and warming areas, suggesting that climate change may play a role.

The study, published on Thursday in the journal Science, shows only correlation with intensive agriculture and temperature, not causation. It does not factor in other circumstances that may be affecting birds along migratory routes or while they are overwintering. But it adds to an ever more robust body of evidence that birds — one of the best measured families of animals on Earth, and a sentinel for the health of other species — are not OK.

Whatever the specific drivers, the accelerating losses make sense given society’s focus on economic growth, which often comes at a cost to the natural world, said Peter P. Marra, an ornithologist and dean at Georgetown University who specializes in bird populations and was not involved with the new research.

“The American dream turns into the American nightmare as we start to look at what we’re doing to biodiversity and systems that we depend on as humans,” he said.