Since 1970, 3 billion birds have been lost in North America, about one in three. know your adaptability to climate crisis is essential for its preservation. Until now, several studies have shown that birds with larger brains tend to survive better In nature. Also, North American migratory birds are shrinking as temperatures have warmed over the past 40 years.
Three researchers from the University of Washington (USA) have discovered that those with very large brains, relative to their body size, did not shrink as much as those with smaller brains.
“It’s not that large-brained species haven’t gotten smaller. Birds with a difference of about twice their brain size (relative to their body size) were able to reduce the effect of heating in their body size by about 70%. But they couldn’t completely escape the changes”, Justin Baldwin, a researcher in Carlos Botero’s laboratory at the University of Washington, both signatories of the work published in the journal ‘Ecology Letters’, tells SINC.
“For example, we found that the forest warbler (Setophaga angelae) family tends to have smaller brains and more decreased body size. However, the New World sparrow family (Passerellidae), with larger brains, have decreased less in body size,” he notes.
The team from the American university based their study on previous work carried out by biologists from the University of Michigan and the Field Museum in Chicago, both in the USA. These works collected specimens of migratory birds in downtown Chicago, in migration season and for about 40 years. The scientists found that, in general, the birds were reducing their body size, probably in response to warming temperatures in the breeding areas.
“We were intrigued that some bird species declined more than others. We thought that perhaps brain size could explain some of this variation in body size changes. In all birds, the species with large brains are those that build tools, live in complex social groups, they manage to persist in harsh environments, live longer, invest more energy in rearing their young, and end up surviving better in the wild. We believed that large brains would also be a key feature that helps birds cope with climate change,” he stresses.
Measure the brains and compare them
To carry out the work, they went to museums and measured the size of the brains of the species. They then combined the data from the Chicago study—which included information on some 70,000 birds that died from colliding with buildings between 1978 and 2016—with their own and used statistical modeling to answer the question: Is the effect of warming temperatures on breeding sites stronger or weaker for species with larger brains?
“This revealed that the effect of climate change is more intense – leading to a greater reduction – for species with smaller brains”, stresses the scientist. The relative size of the brain is often considered a flexibility indicator behavior of birds, although this concept is more controversial in other animal species.
The new results are significant because it is the first time that scientists have been able to demonstrate a direct relationship between cognition and phenotypic responses to climate change. The authors say they can’t conclusively say how warmer temperatures might ultimately decrease bird body size, but consider two possible mechanisms, which could even be happening at the same time.
“First, natural selection might favor birds that can better dissipate heat. This is because the smaller ones have a higher surface area to volume ratio, so being small can help keep them cool. Second, in warmer summers they might have less food available at the time they feed their young,” explains Baldwin.
“In that case, the birds could be getting smaller due to the decrease in food over the years. Regardless of how warmer temperatures lead to smaller body sizes, birds with larger brains seemed to be able to avoid the stronger effects of warming,” he adds.
The challenge of improving its conservation
It is likely that climate change affects entire ecosystems and this could create new interactions between predators and prey, or new habitat associations. Other research has shown that larger-brained bird species could tolerate urbanization and cities, constituting a kind of ‘novel habitat’.
“I think the challenge of promoting population connectivity could depend on the species and region in question, the extent of the changes in the environment, and the magnitude of the species’ responses to these changes,” he says.
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Connectivity between breeding populations is important for the long term survival of species, as fragmented populations can suffer from genetic bottlenecks, low genetic diversity, smaller population sizes and increased risk of extinction. “Other research suggests that migratory routes are changing for some bird species, but it’s not clear to what extent this is widespread across these kinds of species,” he says.
The analysis concludes that smaller species could be subject to particularly strong natural selection, a fact that could be taken into account for the conservation management of these animals.