How climate change can make birds smaller

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Each year, birds migrate in spring and fall. They use the winds that blow through the central part of the country to soar between Canada and Mexico. Many don’t make the massive journey and perish in flight. It’s estimated that more than 600 million birds crash into buildings and die before they reach warmer weather.

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Chicago is one area where the massive skyscrapers filled with glistening windows are problematic. Since this is a heavily traveled migration route, some say that more birds die here than any other city in America. The largest convention center in North America is McCormick Place, and it’s at this very location where most birds meet their demise.

While the collisions are tragic, some fascinating finds are brought to light. For the past four decades, Chicago officials have been collecting birds that perish among the glass buildings. Each bird is cataloged and analyzed. The details have led to a staggering fact. Over the past 40 years, the birds are shrinking in size. Scientists believe this shift is due to climate change.

It all began in 1978 with a scientist named Dave Willard. He heard about the birds constantly perishing by hitting the McCormick Place tower. One day, he was out for a walk, and he happened to stroll by this location. To his surprise, he saw many dead birds lying around the perimeter. He knew that he could use the details of these birds to help prove something, but he wasn’t sure what at this point.

Source: The Field Museum

To date, they’ve collected over 100,000 dead birds, but they only measured and logged the data from 70,716 of them. Every specimen is measured and recorded. He looks at their wingspan, their legs, beaks, and overall length. All the data he collects goes into a handwritten ledger for further analysis.

Willard thought that he would be able to see how the weather patterns had affected birds, but the sheer number of deaths was more significant to scientists. They believed that substantial changes were taking place. The University of Michigan stepped up and wanted to help. Their massive finding was that between the years of 1978-2016, the size of the birds had decreased. Forty-nine different species were affected. The shrinkage was a staggering 2.4 percent. What was causing these changes?

Source: The Field Museum

After much research, the team suggested that global warming had affected these birds. Bergmann’s Rule states that birds that live in colder climates are often larger than those that live in warmer areas. Scientists anticipated that as the weather warmed, changes like this would come into play, but they’ve been talking about it for over 150 years.

Birds have bigger bodies that help them to stay warm in the colder weather. Smaller birds, by design, retain less heat than larger ones. Scientists believe that this massive shift is because the body sizes are dwindling in response to the climate. It doesn’t matter the findings; Willard still plans on collecting and analyzing each bird that meets their demise near that area. One day, he hopes that he will turn the job over to a biologist, but for now, he wants to continue with the journey he started.