Several North American migratory birds are found to shrink in size as temperatures have warmed over the past 40 years. However, the birds with very big brains, relative to their body size, did not shrink as much as smaller-brained birds, said a new research from Washington University in St. Louis.
The first study to identify a direct link between cognition and animal response to human-made climate change, the researchers published the findings in Ecology Letters.
Justin Baldwin, assistant professor of biology in Arts & Sciences at Washington University, notes that as temperatures warm, body sizes decrease. However, larger-brained species are declining less strongly than small brained species, the researcher said.
Baldwin and his co-authors analyzed information on some 70,000 birds that died when they collided with buildings in Chicago from 1978 to 2016. They augmented this vast 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.
BIGGER BRAINS MATTER FOR BIRDS
Relative brain size is often considered a proxy for behavioral flexibility in birds. The idea is controversial when it is applied to some other animals, Baldwin said. However, the researcher said that this 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,” he said.
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.
MORE OR BETTER OPTIONS
It’s not entirely clear why so many songbirds are shrinking in size as temperatures rise. One possible explanation is that heat causes stress, and birds with smaller bodies can dissipate heat better.
“The species we studied only spanned a two-fold difference in relative brain size, which was enough to reduce the effects of increases in breeding temperature by 70 percent,” Baldwin said. “This tells us that even small differences in cognition matter.” The findings also have practical implications for conservation, as 3 billion birds (about one in three) have been lost in North America since the 1970s. That’s probably a lot of natural selection that hits different species differently.” Baldwin said.
“Rapid changes in the environment often produce a few winners and a whole lot of losers, which is really unfortunate,” he said. “Many wildlife populations have moved toward colder places as the planet has warmed. Selection forces those that don’t move to adapt, for example, by changing their body size. Baldwin’s analysis reveals that smaller-brained species might be under especially strong natural selection, a fact that planners may need to take into account for conservation management.
When it comes to climate change mitigation and planning, a major goal is to maintain population level connectivity. Baldwin said. “We want to allow species to move toward the poles or upslope in elevation, to heep up with warming climates. Our findings suggest that this type of intervention could be especially important for smaller-brained species.”
