Brainy birds may fare better under climate change

Many North American migratory birds are shrinking in size as temperatures have warmed over the past 40 years. But birds with big brains relative to their body size did not shrink as much as smaller-brained birds, according to research from Washington University in St. Louis.

The study, supported by the U.S. National Science Foundation, is the first to identify a direct link between cognition and animal response to human-caused climate change. "This study demonstrates the value of long-term records in understanding the effects of climate change and shows that some of these effects are very surprising," said Sam Scheiner, a program director in NSF's Division of Environmental Biology.

The body size changes in songbirds are small but significant, affecting familiar species of sparrows, warblers and thrushes. In fact, the size changes are so pervasive that some scientists have suggested that reductions are a universal response to warming. But the new research published in Ecology Letters shows that bigger-brained birds have been able to "out-think the shrink," at least to a certain extent.

"As temperatures warm, body sizes are decreasing," said biologist Justin Baldwin. "But larger-brained species are declining less than smaller-brained species."

Baldwin and co-authors analyzed information on some 70,000 birds that died when they collided with buildings in Chicago between 1978 and 2016. The scientists augmented this dataset, first published by researchers at the University of Michigan, with new brain volume measurements and lifespan data for 49 of the 52 species of North American migratory birds included in the original study.

Birds that had very large brains, relative to their bodies, had body size reductions that were only about one-third of those observed for birds with smaller brains, the Washington University scientists discovered. And bigger brains matter for birds.

Relative brain size is often considered a proxy for behavioral flexibility. The idea is controversial when it is applied to some other animals, Baldwin said, but it works well 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."

The new findings are significant because this is the first time scientists have been able to show a direct link between cognition and phenotypic responses to climate change.