Due to climate change, birds are getting smaller

Each spring and fall, thousands of birds die when they crash into Chicago’s skyscrapers, which are on a key bird migration route between Canada and Latin America.

But birds do not die in vain. Since the 1970s, many of them have been collected from the street and cataloged by the city’s Field Museum. This unique and detailed set of data was a scientific success, revealing that North American migratory birds appear to be shrinking in response to climate change.

A new study of this data has highlighted an important nuance in this trend: Birds that have larger brains, relative to body size, aren’t shrinking as much as those with smaller brains.

The study is the first to identify a potential link between cognition and the animal’s response to human-induced climate change, according to researchers at Washington University in St. Louis, United States.

“As temperatures increase, body sizes decrease,” Justin Baldwin, a doctoral student at the University of Washington and author of the study published in the journal Ecology Letters, said in a press release. “But the larger-brained species are declining less strongly than the small-brained species.”

According to research, relative brain size is often considered an indicator of behavioral flexibility in birds. The idea is controversial when applied to some other animals, Baldwin said, but it works for birds.

“Relative brain size correlates with greater learning ability, greater memory, greater life expectancy and more stable population dynamics,” said Baldwin.

“In this case, a larger-brained bird species might be able to reduce its exposure to higher temperatures by looking for microhabitats with lower temperatures, for example,” he said.

The researchers analyzed information from 70,000 birds that died after crashing into buildings in Chicago between 1978 and 2016. They added brain volume measurements and life expectancy data for 49 of the 52 species in the database.

The study found that birds that had large brains relative to their bodies, such as the song sparrow and other New World sparrows, had body size reductions of only about a third of those seen for birds with smaller brains. Wood warblers (Parulidae) tended to have smaller brains and tended to shrink more.

“The authors of this incredible study shared their raw data […] which allowed us to add them and find out more,” Baldwin said via email.

Metamorphosis

It is not known exactly why the birds are decreasing in size. Larger body size helps animals in cold places stay warm, while a smaller body retains less heat.

The researchers found that the wingspan of the birds may have increased to compensate for smaller bodies that produce less energy for the incredibly long distances traveled during migration.

Likewise, other research has found that some animals are developing bigger beaks, legs and ears that allow them to better regulate their body temperature as the planet gets warmer. Although most morphological changes occurred in birds, bats and shrews were also affected. Climate change has even altered human bodies.

However, size reduction comes at a potential cost to a bird, with an increased risk of falling victim to predators or making it difficult to compete for resources with other bird species, study co-author Carlos Botero, assistant professor of biology, said in a note. from the University of Washington.

It is in this context that having a bigger brain can offer alternatives that are not available to small-brained species, he said.

“One of the first things that strikes me about these findings is that we can already see that climate change is having a disproportionate effect on species that are less able to cope with environmental change through their behavior,” Botero said.

“This does not mean that climate change is not affecting smart birds. […] or that they will do well. What our findings suggest is that climate change may have a much stronger effect on less intelligent birds.”