How Air Pollution Regulation Can Affect Bird Populations

Original Paper: Liang, Y., Rudik, I., Zou, E.Y., Johnston, A., Rodewald, A.D. and Kling, C.L., 2020. Conservation cobenefits from air pollution regulation: Evidence from birds. Proceedings of the National Academy of Sciences117(49), pp.30900-30906.https://doi.org/10.1073/pnas.2013568117

Featured Image Source: A white-crowned sparrow seen in North America. Credit: Kelly Colgan Azar, 2012. Flickr.

Although we have strong evidence that air pollution poses significant health risks to humans, how air pollutants affect plants and animals is not well studied. Birds are especially susceptible to air pollution because they have a unique way of breathing and interacting with air. Therefore, a group of scientists headed by Dr. Yuanning Liang, Dr. Ivan Rudik, and Dr. Eric Zou conducted a study on how air pollution affects North American birds and how air quality regulations, which were initially created to benefit humans, can also benefit these bird species.

How Bad is Air Pollution for Birds?

The atmosphere we breathe is made up of a combination of many chemicals, including oxygen (O2). Sometimes a chemical reaction occurs in the presence of intense sunlight to break the two oxygen atoms apart, and ozone (O3) is created when these atoms recombine into groups of three. There is a natural ozone layer high up in the atmosphere which shields things on earth from harmful ultraviolet rays. However, ozone can also form at ground level when natural and man-made emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) from gasoline combustion and other pollutants react with sunlight.

Ozone not only causes birds physical harm (for example, by affecting their breathing and respiratory systems), but it can lead to changes in bird habitat, food supplies, and interactions between different species. Therefore, understanding the negative relationship between bird populations and ozone is important for bird conservation and health.

Air pollution from a smokestack in New Jersey, USA. Credit: John Isaac, United Nations Photo, 2005. Flickr.

To collect their data on how air pollution affects birds, researchers used eBird, a site and app where citizen scientists and birdwatchers can record any instances of birds they see or hear in the wild. An entry includes information such as the species and behavior of the bird, any pictures taken of it, and where and when it was seen. This information is then reviewed by experts in the field and is aggregated by the site to create interactive maps and large-scale observation data that can be used for research purposes, environmental impact assessments, and other work done by environmental professionals.

The study included eBird data from over 11 million observations collected in the United States between 2002 and 2016. Using these data, the researchers created a statistical model that estimated bird abundance over time across the United States. To compare the model to the data, researchers contrasted the model to independent data collected by scientists to understand the changes in bird populations over time.      

After getting these population estimates, the researchers created a database that tracks monthly changes in bird abundance, air quality, and pollution regulation status across the US over a 15-year period. Then they estimated the effects of ozone and fine particulate matter on bird abundance. They looked at these air pollutants in the model because those are the most likely to harm human health and increase mortality risks. They found that an increase in ozone is associated with decreased bird abundance, but there was no connection between fine particulate matter and bird abundance.

Effects of Ozone Regulations on Bird Abundances

An important tool to fight back against air pollution is the creation of policies which regulate the quantities of pollutants that can be released to the air. For example, the NOx Budget Trading Program (NBP) is an air quality regulation originally designed to limit summertime (from May 1st to September 30th) ozone emissions from large industrial sources. States in the eastern part of the US generally have these regulations, whereas states in the middle and western parts of the US do not.

After determining the relationship between bird abundance and air pollutants, the researchers compared bird abundances in states with and without the NBP. By incorporating data on NBP regulations, they were able to isolate the changes in air pollution and abundance specific to each state. They found that having an NBP both decreased ozone concentrations per county by 4.2 parts per billion on average and also increased overall bird abundance. Specifically, land bird abundances increased, but abundances of waterfowl, shorebirds, and waterbirds did not change. In addition, birds that weighed less than 142g increased in abundance in areas with the NBP, but larger birds were unaffected. Most land birds are quite small and weigh less than 142g, so these two metrics may be related. One reason these small land birds might be positively affected by the NBP is that ozone reduces the number of insects, and many of these birds are highly reliant on insects for their food.

Red-winged blackbirds at the Village Creek drying beds in Arlington, Texas, USA. Credit: TexasEagle, 2014. Flickr.
What If There Were No Ozone Regulations?

Finally, the study looked at what might have happened over time without regulations on ozone emissions and compared this scenario to what actually happened. Ozone was first measured and regulated by the EPA in 1980, so researchers created a model that estimated annual trends in ozone concentrations starting then. The largest declines in ozone have been in states with NBP regulations, and overall ozone has declined 0.13 parts per billion every year on average between 1980 and 2018. Then the researchers determined the average number of birds that die per unit of ozone emitted. With this information, they established both the trend in bird abundance in relation to ozone levels that actually occurred during this time and the trend that would have occurred if these ozone levels had remained steady since 1980.  An additional 1.5 billion birds would have died over these four decades if ozone emissions had not declined, which is 50% more birds than those that actually died during this time. Currently there are about seven billion birds in the US, and the survival of about 20% of this population can be attributed to the decrease in ozone concentrations resulting from increased regulations.

Though this study only looked at bird populations in the US in relation to ozone and fine particulate matter, the results suggest that other widespread declines in populations of other species could be prevented or reversed as air quality improves, and that many regulations put in place to benefit humans can also provide substantial benefits to wildlife.

What Can You Do to Help?

Though most ozone emissions come from large industries and halting ozone emissions relies heavily on federal regulations to stop these emissions, small actions you take can also help make a difference. For instance, you can take less trips in your car, use stoves and fireplaces less frequently, and try not to use gas-powered outdoor equipment unless necessary. In addition, you can advocate for air pollution regulations in the city or state you live in to make sure they remain in place. This might include writing a letter to your local government, speaking at a town meeting, or voting for people in positions of power who have a platform that includes a plan to reduce air pollution.

You can also help provide data that scientists and governmental agencies can use to monitor birds and other wildlife, just like in this study. It’s free to sign up for eBird, and anyone can use it once they make an account. There’s even a mobile app where you can upload your observations. Though eBird is only for bird-related sightings, there are a number of other free apps available where you can record your observations. iNaturalist is a great site to use, as you can report any type of wildlife, each entry is reviewed by experts, and it’s frequently used by researchers and agencies to collect data. It will even give you identification suggestions if you’re unsure what you’ve spotted in the wild. So get out there and explore!

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Jessica Espinosa

Jessica Espinosa

Hi! My name is Jessica Espinosa and I am a PhD student at UConn in the Ecology and Evolutionary Biology Department interested in the bird conservation. I received my masters degree in Conservation Biology from Columbia University where my thesis focused on the effects of coastal pollution on the behavior and morphology of hermit crabs in Fiji. I am also a Mount Holyoke College and City Year Alum. In my free time, I enjoy reading, writing, hiking, doing martial arts, and playing music.

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