Researchers have found that climate change is making severe impacts on birds in diverse ways from all over the world. Their sizes are getting shrunk due to climate changes. David Willard, a Field Museum ornithologist, measured Chicago’s dead birds that died after colliding into building in Chicago since 1978. More than 100,000 dead birds collected as specimens for the Field Museum of Natural History.
Investigations revealed the length of the birds’ legs are growing shorter on average, they are losing weight and wings are getting slightly long in size. From 1978 to 2016, the length of the bird’s lower leg bone shortened by 2.4%, while the wings increased by 1.3%.
Benjamin Winger, the study author at the University of Michigan, said, “Warming temperatures seem to be having a pretty consistent and almost universal effect on a large number of different species, regardless of other aspects of their biology.”
Every year, near about 600 million birds die in the United States after colliding with skyscrapers that fall on the migration path. Mr. Willard collected a vast range of specimens of the birds making their epic journey between Canada to Latin America. "I've just stopped for the season. The number of birds we get each day is highly variable, depending on whether it's a big day of migration. The maximum is 300 in a day," he said.
“In years when temperatures were a bit warmer, the bodies got smaller. In years when temperatures were a bit cooler, we saw an increase in body size, even though the long-term trend was to decline,” Winger said.
However, there is no exact explanation to the scientists why the birds are getting smaller in size due to warmer temperatures. A theory says, smaller animals take a short time to cool down, losing their body heat more quickly due to their larger surface-area-to-volume ratios.
According to another scientist, the chances of surviving for migratory birds get increased with longer wingspans. It compensates smaller bodies to produce less energy to make long distances during migrations.
The researchers claimed that they would continue to observe the database whether the shape change is a result of a process called developmental plasticity. The method indicates the ability of an animal to modify its development in response to a changing environment.
Brian Weeks, an assistant professor at the University of Michigan School for Environment and Sustainability, said that "We had good reason to expect that increasing temperatures would lead to reductions in body size, based on previous studies."
The biologists also claimed that the changes in the bird’s body shape are subtle, not detectable by the human eye. There is another pattern described by the researchers as Bergmann’s rule. According to Bergmann’s rule, animal species, individuals tend to be smaller in warmer parts of their range as smaller bodies need less heat.
"We found almost all of the species were getting smaller," said lead author Brian Weeks, an assistant professor at the school for environment and sustainability at the University of Michigan.
"The species were pretty diverse, but responding in a similar way," he added.