Clean Air Act saved 1.5 billion birds, study shows

US pollution regulations designed to protect humans from dirty air are also saving the birds. Thus concludes a new continental study published today in The Proceedings of the National Academy of Sciences. The study authors found that improving air quality as part of a federal program to reduce ozone pollution may have prevented the loss of 1.5 billion birds over the past 40 years. Today it is nearly 20% of bird life in the United States. The study was led by scientists from Cornell University and the University of Oregon.

“Our research shows that the benefits of environmental regulation have probably been underestimated,” says Ivan Rudik, lead author and Ruth and William Morgan Assistant Professor at Cornell’s Dyson School of Applied Economics and Management. “Reducing pollution has positive impacts in unexpected places and provides additional political leverage for conservation efforts.”

Ozone is a naturally occurring gas and is also produced by human activities, including power plants and automobiles. It can be good or bad. An ozone layer in the upper atmosphere protects the Earth from the sun’s harmful ultraviolet rays. But tropospheric ozone is dangerous and is the main pollutant of smog.

To examine the relationship between bird abundance and air pollution, the researchers used models that combined bird observations from Cornell Lab of Ornithology’s eBird program with ground-level pollution data and existing regulations. They tracked monthly changes in bird abundance, air quality, and regulatory status for 3,214 U.S. counties over a 15-year period. The team focused on the NOx (nitric oxide) balance exchange program, which was implemented by the US Environmental Protection Agency to protect human health by limiting summer emissions of ozone precursors from large industrial sources.

The study results suggest that ozone pollution is most harmful to small migratory birds (such as sparrows, fledglings and finches) which make up 86 percent of all North American land bird species. Ozone pollution directly harms birds by damaging their respiratory systems and indirectly affects birds by damaging their food sources.

“Not only can ozone cause direct physical harm to birds, but it can also compromise plant health and reduce the number of insects birds consume,” explains study author Amanda Rodewald, Professor Garvin in the Department of Resources. Environmental and Natural Sciences of Cornell and Director of the Center for Avian Population Studies at the Cornell Lab of Ornithology. “Unsurprisingly, birds that cannot access high-quality habitats or food resources are less likely to survive or reproduce successfully. The good news here is that environmental policies designed to protect human health also have important benefits for birds.” .

Last year, a separate study from the Cornell Lab of Ornithology showed that North American bird populations have declined by nearly 3 billion birds since 1970 (Rosenberg et. in. Science, 2019). This new study shows that without the regulations and ozone-depleting efforts of the Clean Air Act, the loss of bird life could have been 1.5 billion more birds.

“This is the first large-scale evidence that ozone is associated with declining bird abundances in the United States and that life-saving regulations also bring significant conservation benefits to birds,” says Catherine Kling, professor of the Tisch University at Cornell Dyson School of Applied Economics and Management and Faculty Director at Cornell’s Atkinson Center for Sustainability. “This work contributes to our growing understanding of the connection between environmental health and human health.”