Agriculture Intensity Drives Accelerating Bird Loss Across Three U.S. Regions

North American bird populations have been losing ground for decades. A 2019 study estimated that the continent has lost roughly 3 billion birds since 1970. But aggregate decline numbers obscure something important: whether the rate of loss is constant, speeding up, or slowing down - and where the worst deterioration is concentrated.

A study published February 26, 2026 in Science provides the first systematic picture of acceleration and deceleration patterns in bird abundance change across North America, and traces the hotspots of worsening loss to a specific driver.

The analysis, led by Francois Leroy, a postdoctoral scholar at The Ohio State University, used data from 1,033 routes in the North American Breeding Bird Survey - an annual multinational program that has tracked continental bird populations since the 1960s. The team analyzed abundance trends for 261 species across 54 avian families and 10 habitats from 1987 to 2021.

Where Abundance Is Falling Fastest

Across all survey routes, bird abundance declined by approximately 15% per route over the 35-year period. Among the 261 species tracked, 122 - or 47% - showed statistically significant declines. Among those declining species, 63 showed evidence of accelerating deterioration: their populations are not just shrinking but shrinking faster each year.

Mapping these acceleration rates revealed three regional concentrations: the Midwest, California, and Mid-Atlantic states. A small region just north of the U.S.-Canadian border was the only area where total bird abundance had increased.

The pattern holds across a wide range of species types. Twice as many species showed accelerating decline compared to decelerating decline. The same pattern was consistent at the family level - meaning it crosses taxonomic boundaries and affects birds with very different ecological roles, habitat preferences, and life histories.

"The impact is not only on a few species with the same traits or only on farmland bird species," Leroy said. "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."

Agricultural Intensity as the Top Predictor

To explain why those three regions showed the fastest deterioration, the team examined a range of potential drivers: temperature change, precipitation, land cover, cropland extent, fertilizer application rates, pesticide usage changes, and a composite metric called the human footprint that integrates population density, infrastructure, and energy use.

Agriculture intensity - measured through cropland extent, fertilizer use, and pesticide application - emerged as the strongest predictor of where accelerating declines were concentrated. The geographic overlap between the Midwest hotspot (the largest of the three) and intensive corn-soybean agriculture, California's irrigated specialty crop regions, and Mid-Atlantic agricultural zones was not coincidental.

The study is correlational, and the researchers are clear that they cannot determine which specific agricultural factor - cropland expansion, pesticide type, application timing, or cumulative exposure - is most responsible. That limitation matters for intervention design: knowing that agricultural intensity is the main predictor does not immediately tell policymakers which agricultural practices to change first.

"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," Leroy said.

What the Losses Mean Ecologically

Birds provide services that are difficult to replace. Insectivorous birds regulate populations of crop pests and disease-carrying insects. Frugivores disperse seeds across distances that promote plant genetic diversity and forest resilience. Many large raptors and predators depend on bird populations as prey. A 15% continent-wide decline in abundance per survey route, with accelerating losses in some of the most productive agricultural regions, has cascading effects that extend well beyond bird watching counts.

Leroy frames the situation with qualified optimism: "Biodiversity is very dynamic. 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."