What Dirty Old Birds Can Teach Us About Air Pollution

Bird specimens at the Field Museum of Chicago

It couldn’t help but attract my attention; a neat row of old, preserved birds, their soft, feathery chests face-up: some were dark with soot, others by comparison, were clean. All came from an industrial area in the United States called the Rust Belt. That is key to the story.

The birds are part of a collection at The Field Museum in Chicago that dates back to the early 1900s. For a number of years, researchers and museum visitors had been noticing that some of the bird specimens looked clean while others appeared dirty. So recently, scientists from the museum and the University of Chicago decided to take a sharper look and see if they could come up with an answer.

What birds can tell us about black carbon pollution

The above red-headed woodpeckers and the yellow-throated larks (below) formed part of a study just released from the National Academy of Sciences that provided a surprising answer to the question. To decipher why some of the birds were more dirty than others, researchers studied over 1,300 museum specimens. What they discovered was that the birds’ degree of cleanliness corresponded directly with levels of air-borne pollution during their lifetimes, specifically black carbon.

Horned lark specimens

The birds’ chest feathers turned out to be a perfect tool for tracing the amount of black carbon that was present in the air over time. Why? Because the soot clung to their feathers and accumulated year after year.

“These birds were acting as air filters moving through the environment” said Shane DuBay, a graduate student at The Field Museum and the University of Chicago and one of the authors of the study. “The soot on these birds’ feathers allowed us to trace the amount of black carbon in the air over time, and we found that the air at the turn of the century was even more polluted than scientists previously thought,” he said.

Brown coal, which is used to power electricity, has a carbon content of 70-80 percent

Coal and black carbon

According to the Center for Climate and Energy Solutions, black carbon (BC), a long-known source of health and environmental concerns, has also recently emerged as a major contributor to global climate change, second only to C02. Until the mid-1950s, however, direct environmental samples were hard to come by.

Red-headed woodpecker

The birds, however, had lived in the part of the U.S. known as the manufacturing belt, a highly industrialized region historically reliant on coal. By analyzing the different specimens and plotting them on a time line, the researchers were able to go back in time and develop a correlation between the birds’ sootiness and a century’s worth of industrial and environmental approaches to combatting black carbon pollution. This gave them key insights into just how effective these policy approaches were.

For instance, during the depression, when there was a sharp drop in coal production, there was a drop in soot on the birds, too. Birds got dirtier again during World War II when wartime manufacturing drove up coal use. Birds got cleaner when people in the Rust belt started switching to gas to heat their homes in lieu of coal.

What is surprising to those of us who are worried about air pollution, is that the more recent specimens’ feathers are actually cleaner than those of the turn of the century (when we first started collecting birds, apparently).

Today’s horned larks are a lot cleaner

Still, the birds could be picking up less detectable amount of pollutants from other sources. All interesting things to ponder as the United States debates the future of coal, which currently provides 30 percent of the country’s energy. Meanwhile, the dirty birds provide silent testament to the legacies of our sooty history.


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