Many bird species are slowly but surely getting smaller. One study from 2019 looked at more than 70,000 North American migratory birds across 52 species that met untimely ends by flying into Chicago buildings from 1978 to 2016. It suggests that birds in this diverse set had consistently grown smaller as the summers had grown hotter through climate change over the past 40 years.
While this shrinking was observed across these migratory species, new research suggests that birds with bigger brains—relative to their body size—aren’t shrinking like their smaller-brained kin. The research posits that birds like corvids may be better able to survive climate change simply because they are “smarter” in some sense.
Justin Baldwin, a PhD candidate at Washington University and one of the authors of the paper, said that brain size isn’t always a useful proxy for intelligence. But—and we’re not sure why—it does appear to hold true for many birds. “The birds with big brains are basically the ones that build tools, live in complex social groups, live and remain in harsh environments, live longer, [put] more time and energy into raising babies, and [survive] better in the wild,” he told Ars.
To determine how the brainier species were handling climate change, Baldwin and his team looked over the data from the 2019 paper and added some of their own. They looked at the brain volume of specimens from various universities that covered 49 of the 52 species in the earlier study. In addition, the research team checked the literature about the species’ natural lifespans and tried to get a sense of how quickly mutations occur in the population from generation to generation so they could understand how fast the species might be mounting an evolutionary response.
According to Baldwin, there are two likely reasons behind birds getting physically smaller. The first is that they are evolving that way to deal with climate change—birds with smaller bodies may be able to dissipate heat better, a boon when dealing with increasingly warm summers, for instance. The second is that food availability could be decreasing over time, hindering the birds’ development over generations. “We don’t know exactly how birds have been shrinking,” he said.
In either case, it seems that brain size is associated with some species shrinking more slowly than others. According to Baldwin, this could simply be because many of these species have longer lives, so changes in their physiologies from generation to generation could come slower.
Alternatively, the bigger, arguably smarter birds might be able to figure out how to adapt to climate change better than birds with smaller brains. Baldwin said it’s possible that the birds are capable of finding cooler places to hang out during heatwaves, which can help their chances of survival. “In both cases, regardless of the mechanism by which birds are shrinking, species with big brains should experience weaker effects [from climate change],” he said.
Baldwin noted that birds with smaller brains are liable to become more vulnerable to changes in the environment in the future. This is particularly worrying because in Canada and the US, around three billion birds—or about 30 percent—have died off compared to population estimates during the 1970s. “We see our research as being able to help prioritize conservation efforts for those particularly sensitive and susceptible species such as the ones with small brains,” he said.
Ecology Letters, 2022. DOI: 10.1111/ele.13971 (About DOIs)