Yuanning Liang, Ivan Rudik, Eric Yongchen Zou, Alison Johnston, Amanda D. Rodewald, and Catherine L. Kling

PNAS December 8, 2020 117 (49): 30900-30906 – Environmental Science

Significance

Understanding the drivers of abundance and biodiversity decline across numerous taxa is imperative for designing conservation policy. We use highly detailed citizen science data to show that there is a strong, robust negative association between bird abundance and ambient ozone concentrations in the United States. In particular, we find that a regulation aimed at reducing ozone precursors has significantly bolstered populations in the eastern United States. Our estimated effects suggest that the large decline in average US ozone concentrations over the past several decades has averted the loss of potentially billions of birds. Environmental policies nominally aimed at humans can also provide substantial benefits to other species.

Abstract

Massive wildlife losses over the past 50 y have brought new urgency to identifying both the drivers of population decline and potential solutions. We provide large-scale evidence that air pollution, specifically ozone, is associated with declines in bird abundance in the United States. We show that an air pollution regulation limiting ozone precursors emissions has delivered substantial benefits to bird conservation. Our estimates imply that air quality improvements over the past 4 decades have stemmed the decline in bird populations, averting the loss of 1.5 billion birds, ∼20% of current totals. Our results highlight that in addition to protecting human health, air pollution regulations have previously unrecognized and unquantified conservation cobenefits.

See: https://www.pnas.org/content/117/49/30900

Fig. 3.

(A) Effects of the NBP on ozone and bird abundance in SD units. (B) Implied effects of ozone from results in A, as calculated using an IV approach that combines the effect of the NBP on ozone and the effect of predicted ozone on bird abundance. Birds are classified into groups following previous work (24). Bird groups by mass are divided into four quartiles according to their mass distribution. The black bars indicate 95% confidence intervals. SEs are clustered at the state–season level and robust to heteroskedasticity. The regressions are weighted by the number of checklists in a given county–year–month. The IV first stage F statistics in estimating the effect of NBP on bird groups from the second to the last row range from 22.39 (mass < 16 g) to 22.67 (shorebird). ***P < 0.01, **P < 0.05, *P < 0.10.