Hotspots of accelerated bird decline linked to agricultural activity

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Hotspots of accelerated bird decline linked to agricultural activity

Study: Midwest, California, Mid-Atlantic show quickening pace of loss

Though previous research has shown that bird populations are declining across North America, a new study is the first to show that the pace of loss has picked up speed since the mid-1980s in three regions: the Midwest, California and Mid-Atlantic states.

After these hotspots of accelerated bird decline were revealed, researchers looked for factors that could explain the difference in the rates of decline, examining climate measures and human activity-related data.

A top predictor of where the accelerated abundance loss occurred became clear, overlapping with locations of agriculture intensity as indicated by the extent of cropland and the use of fertilizer and pesticides.

"Agriculture intensity is the main driver associated with accelerated loss of abundance, but we cannot disentangle which of these three metrics is most important because this is a correlative analysis," said lead author François Leroy, a postdoctoral scholar in evolution, ecology and organismal biologyat The Ohio State University.

"But the impact is not only on a few species with the same traits or only on farmland bird species. Twice as many species showed accelerating decline compared to decelerating decline, and the same pattern was seen at the family level. That means it is occurring at a very large taxonomic scale - a lot of different species with different functional traits are affected, and it's systemic."

The study is published today (Feb. 26, 2026) in Science.

Data for the primary analysis came from the North American Breeding Bird Survey, an annual multinational monitoring program tracking North American bird populations.

Using 1,033 routes from the survey data, the researchers analyzed abundance change and the rate of that change, both acceleration and deceleration, for 261 bird species, 54 avian families and 10 habitats from 1987 to 2021 - a date range providing the best combination of records covering both space and time.

Overall, the results showed a continent-wide decline in the abundance of all birds, with 122 species - 47% of those tracked - showing significant declines. Among those, accelerated decline was detected in 63 species. There was only one small region, just north of the U.S.-Canadian border, where total bird abundance had increased.

Leroy and colleagues did not focus on extrapolating figures to quantify the number of birds lost, instead estimating a 15% total loss of abundance of birds per route across North America over 35 years.

"We worked at the local scale in order to be as conservative and reliable as possible," he said. "With this kind of change at the global scale, when you find that there is a 15% loss all across the U.S., that means something statistically. It represents a strong message.

"Basically, the decline is everywhere, and then there is a spatial variation of this acceleration - these three hotspots. And the Midwest hotspot is quite big."

In an effort to explain the acceleration, the team turned to datasets on a range of factors with potential to affect bird abundance: mean temperature and temperature change, precipitation, land cover (grassland, tree, shrub, water), cropland cover change, fertilizer use, pesticide usage change, vegetation change and the human footprint- a metric of human impacts taking into account population density, infrastructure and energy usage.

"What we found was that agriculture intensity was the main predictor of those hotspots of accelerated decline, and that was the case for the map that was smoothed to detect patterns and even for the raw output of the model," Leroy said.

This widespread loss of birds - through both deaths and lower birth rates - has consequences. Among birds' most significant ecosystem services are regulating insect populationsand spreading plant seedsin ways that can promote genetic diversity and increase plant resilience. They are also an important element of the food chain on which many large birds and other wildlife rely.

That human factors are at play in bird loss is not entirely surprising: Leroy first took on the investigation of the accelerated decline in bird abundance based on metrics that show an acceleration of humans' influence on the global environment since the 1950s.

"We know there is a relationship between human activities and biodiversity because we know that humans, like any other species, have an impact on the environment," he said.

Even so, Leroy said he has hope for better days ahead for birds.

"Biodiversity is very dynamic," he said. "If you let life come back, if you leave space and take the right measures, you will see results on biodiversity quickly - let's say, in a matter of decades. If we act, we will see the impact in our lifetime."

Co-authors of the paper were Marta Jarzyna, associate professor of evolution, ecology and organismal biology at Ohio State, and Petr Keil of the Czech University of Life Sciences.

This work was supported by the European Union, the U.S. National Science Foundation and the Czech Science Foundation.

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