As the climate warms up, birds are shrinking and wingspans are increasing. The researchers collected and analyzed 7716 specimens in North America for 40 years. Birds were killed and sampled after they crashed a building in Chicago, Illinois.
"The most important findings from the study are how animals adapt to climate change," the researchers said. "I found out that almost all of the birds are getting smaller," said Assistant Professor Brian Weeks, University of Michigan Environment and General Manager of the study. "Algae were quite diverse, but they responded to climate change in a similar way. The consistency was amazing."
He said animal studies on climate change have often focused on geographic changes, such as migration or birth, or at certain times of life. However, this study offers another perspective in terms of morphology.
"This is an important allusion," Professor Wekes said. "It would be difficult to understand how living things adapt to the environment without considering all three aspects."
The study found that between 1978 and 2016, bird's leg bones were 2.4% shorter. Leg length is a common criterion to guess the size of a bird. At the same time, wings grew 1.3%. The study analyzes that global warming has reduced the size of algae and the wings.
"The movement of birds is a tremendous amount of energy," Professor Wekes said. "The advantage is that small-sized birds have the advantage of spending less energy in moving their habitat." In the end, he concluded that birds with large wings and small size survive best.
The scientific community has not been able to pinpoint exactly what causes birds to shrink in warmer climates. One theory of this is that small birds are becoming smaller because they are advantageous for lowering body temperature by increasing the surface-to-weight ratio.
Weeks said the work was possible thanks to "Will Cruelty" by Dave Willard, co-author and ornithologist at the Chicago Field Natural History Museum.
Since 1978, Willard began to wander around skyscrapers in order to collect migratory birds that were killed in the building during the spring and autumn relocation.
Birds travel mostly at night. Birds are prone to artificial lighting in skyscrapers. Therefore, it is easy to die by hitting the window. It is estimated that hundreds of millions of birds die each year.
"Willard didn't collect it for research," Professor Wekes said. "I thought it would be useful someday."
Over the years, many people and scientists have volunteered to help collect Willard's specimens. He acquired 7716 specimens in this way and used them in his research. Professor Weeks added that the sample was "the best standard."
This research is attracting attention as data demonstrating that not only algae but also other organisms are shrinking in response to climate change.
In 2014, the researchers found that goats in the Alps get smaller as the temperature warms up. Another study that same year reported that salamanders are shrinking rapidly due to climate change.