The study is the first to identify a potential link between cognition and animal response to human-made climate change, according to the researchers from Washington University in St. Louis.
Relative brain size is often considered an indicator of behavioral flexibility in birds, according to the research. The idea is controversial when it’s applied to some other animals, Baldwin said, but it works for birds.
“Relative brain size correlates with increased learning ability, increased memory, longer lifespans and more stable population dynamics,” Baldwin said.
“In this case, a bigger-brained species of bird might be able to reduce its exposure to warming temperatures by seeking out microhabitats with cooler temperatures, for example,” he said.
The researchers analyzed information from 70,000 birds that died when they collided with buildings in Chicago between 1978 and 2016. They added brain volume measurements and life-span data for 49 of the 52 species in the database.
Birds that had big brains, relative to their bodies such as the song sparrow and other New World sparrows, had body-size reductions that were only about one-third of those observed for birds with smaller brains, the study found. Wood warblers (Parulidae) tended to have smaller brains and tended to shrink more.
“The authors from that amazing study shared their raw data … which allowed us to add to it and discover more,” Baldwin said via email.
It’s not known exactly why birds are shrinking in size. Larger body size helps animals in cold places stay warm, while a smaller body retains less heat.
Bird wingspans may have increased to compensate for smaller bodies that produce less energy for the incredibly long distances traveled during migration, researchers have also found.
However, downsizing comes at a potential cost for a bird, with an increased risk of falling prey to predators or making it harder to compete for resources with other bird species, said study coauthor Carlos Botero, assistant professor of biology at Washington University, in the statement.
It’s in this context that having a larger brain may offer alternatives that are not available to small-brained species, he said.
“One of the first things that jumps out to me from these findings is that we can already see that climate change is having a disproportionate effect on species that have less capacity to deal with environmental change through their behavior,” Botero said.
“This doesn’t mean that climate change is not affecting brainy birds … or that brainy birds are going to do just fine. What our findings suggest is that climate change can have a much stronger effect on the less-brainy birds.”