In a paper released on November 24, 2020, researchers from Cornell University concluded that the Clean Air Act not only has saved human lives, it has spared 1.5 billion avian lives. The reason is the reduction of ground level ozone concentrations resulting from tightening restrictions under the Act.
Ozone harms birds’ respiratory systems. Small migratory birds, such as finches, warblers and sparrows benefitted the most from a reduction in ozone concentration. The authors used models that matched data on long-term bird abundance across the U.S. with pollution readings and regulatory enforcement information.
Between 1980 and 2018, ozone levels dropped significantly, with biggest declines found in Eastern states covered by an EPA program to reduce nitrogen oxides, which convert to ozone in sunlight.
Despite the positive effects of ozone reduction on bird populations, still the overall bird population is believed to have declined by almost 3 billion since 1970.