• A recent study has found that improved air quality from the US Clean Air Act has saved around 1.5 billion birds.
  • Before the 1970 Act, ozone pollution had been damaging their respiratory systems as well as their food sources.
  • This pollution is most harmful to small migratory land birds, which make up 86% of all North American species.

The improved air quality and reduced ozone pollution that followed the 1970 passage of the US Clean Air Act and later amendments have saved the lives of 1.5 billion birds across the continent, according to new research.

The research shows that pollution regulations that are nominally designed to protect human health can provide value for other species as well, says Eric Zou, an assistant professor in the economics department at the University of Oregon and the National Bureau of Economic Research.

“Our paper takes a first stab at this possibility by looking at the effect of a pollution regulation on birds, one of the only species whose presence and abundance have been measured systematically in the past several decades,” Zou says.

“We found evidence that the regulation-induced pollution reduction has provided substantial benefits to birds abundance,” he says.

Such benefits of environmental regulation have likely been underestimated, says lead author, Ivan Rudik, of Cornell’s Dyson School of Applied Economics and Management. Reducing pollution, such as ozone, can have positive impacts in unexpected places and provide an incentive for conservation efforts, he says.

Ozone is a gas that can be good or bad. It occurs in nature and is also produced by power plants and cars. A layer of ozone in the upper atmosphere protects the Earth from the sun’s harmful ultraviolet rays, but ground-level ozone is hazardous and a primary pollutant in smog.

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North American bird populations declined by nearly 3 billion birds since 1970.
Image: Science Magazine

To explore connections between bird abundance and air pollution, the research team used models that combined bird observations from the Cornell Lab of Ornithology’s eBird program with ground-level pollution data and existing regulations.

Zou, an environmental economist, says the team asked him to join to help in the study’s design and statistical analyses because of expertise in using economic tools to study environmental topics.

The researchers tracked monthly changes in bird abundance, air quality, and regulation status for 3,214 US counties over a span of 15 years. They focused on the NOx Budget Trading Program, which was created in 2003 to reduce the regional transport of nitric oxide emissions from power plants and other large combustion sources in the Eastern US.

The study’s findings suggest that ozone pollution is most detrimental to small migratory land birds such as sparrows, warblers, and finches, which make up 86% of all North American species. Ozone pollution directly harms birds by damaging their respiratory system and indirectly affects birds by harming their food sources.

Last year, a separate study in Science by the Cornell Lab of Ornithology showed that North American bird populations declined by nearly 3 billion birds since 1970. The impacts of the Clean Air Act, as the researchers found in the new study, protected bird populations from even greater losses.

Zou was drawn to the project, he says, by its interdisciplinary approach. “Economists these days study a wide variety of topics, and there is a branch known as environmental economics that looks at the interaction between the environment and human society,” he says.

“Economists care about the cost and benefits of policies, and we’ll go extra miles to study the unknowns of these policies.”

The data and evidence found in the new study, he says, point to a co-benefit for other species from a policy designed to benefit humans with cleaner air.