Big-Brained Birds Aren't Shrinking As Much With Climate Change

Size matters … at least when it comes to bird brains and the ability to deal with warming temperatures.

As climates have warmed over the past century, many bird species have become smaller. But some birds with very big brains haven’t shrunk in the same way, new research finds.

Studies have shown that many North American songbirds and birds in the Amazon rainforest have changed in body size as temperatures have increased. The difference hasn’t been substantial, but it has been significant enough that some scientists have suggested it’s a universal response to climate change.

But new research finds that the body size reductions aren’t happening across the board with some large-brained birds having much less significant changes.

The results were published in the journal Ecology Letters.

For the study, researchers studied information on about 70,000 birds that had died when they collided with buildings in Chicago from 1978 to 2016. They added data on brain volume and lifespan for 49 of the 52 species of migratory birds in the original study.

They found that birds with very large brains had reductions in overall body size that were about one-third of the reductions noted in birds with smaller brains.

“We discovered that birds with large brains (relative to their body size) shrink less than birds with small brains, given the same amount of climate warming,” study co-author Justin Baldwin, a Ph.D. candidate at Washington University in St. Louis, tells Treehugger.

“We think that birds with large brains (relative to their body size) might be able to better use their capacity for complex and flexible behavior to survive challenging environmental conditions. For example, this could be doing a better job of staying cool during heat waves or finding food during famines.” 

Why Size Matters

Bigger brains make a difference for birds.

“In birds, the species with big brains are the ones that build tools, live in complex social groups, manage to persist in harsh environments, live longer, invest more time and energy into raising babies, and end up surviving better in the wild,” Baldwin says.

“We think that big brains might be a key characteristic that helps birds deal with climate change.”

Researchers aren’t certain exactly how warmer temperatures might lead to decreasing body size in birds, but they are considering two possible explanations, which could even be happening simultaneously.

“First, natural selection might be favoring birds that can dissipate heat better. This is because smaller birds have higher ratios of surface area to volume, so being small can help birds stay cool,” Baldwin says.

“Second, warmer summers might have less food available for birds at the time when they are feeding their babies. In that scenario, birds might be getting smaller because of decreased food over the years.”

The findings don’t suggest that climate change is having zero impact on bigger-brained birds.

“But birds with bigger brains might be able to avoid some of the harshest impacts of climate change,” Baldwin says. “Even though we found that birds with about a two-fold difference in brain size were able to reduce the effect of warming by about 70%, they were unable to escape the changes entirely.”

Researchers believe their findings are important because they can inform climate change mitigation and planning.

“First, our research can help set conservation priorities, as it suggests that small-brained species can be more susceptible to warming temperatures,” Baldwin suggests.

“Second, it can help explain why researchers have been finding such a puzzling variety of responses to climate change—we think that having big brains is a unifying feature that helps all birds deal with the challenges of a changing world.”