Researchers uncover the reason crows and ravens are found across the globe

(CN) — Researchers at Washington University in St. Louis traced the evolution of crows and ravens to determine what allows the birds to survive in some of the most varied environments on Earth.

The study, published Thursday in the journal Nature Communications, found that species of crows and ravens are able to exist today from the Arctic tundra to the Sonoran desert thanks in large part to traits from their earliest ancestors that make them extremely adaptable.

Carlos Botero, assistant professor of biology, said the research team found that the diverse, global array of crow and raven species developed quickly compared to similar animals. Botero said the crows and ravens are an example of global diversification, in which the lineage of a species begins utilizing more and more space, eventually spreading to new continents and “in comparatively a short period, suddenly there’s a generation of a range of different species.”

“As soon as the ancestral crow arises in the picture, there’s a great increase in the number of new species,” said Botero. “That comes along with generation of diversity in forms of how big they are, how their beak shape looks and what ecological niches they occupy.”

Botero said that even as the birds diversified across the globe and their body sizes changed, they never got smaller. Rather, all the species retained a relatively large size. He also said that the shape of the beaks changed quickly among the different crow and raven species, allowing them different ways of using their beaks to find and handle food.

Perhaps most interestingly, Botero said the species’ role in their ecosystems — or their ecological niche — also diversified. They began to evolve to occupy drier habitats and expand their environments.

After determining that the crows and ravens were able to rapidly diversify, Botero said the researchers began investigating the traits that allowed the animals to occupy drastically different habitats across the globe.

“What we found is that the ancestral form of crow happened to have three key characteristics,” Botero said. “It was a big animal. It had comparatively wide and long wings, which we know is associated with the capacity to fly long distances. And we found that it had comparatively huge relative brain size.”

Botero said this “trifecta” combination of traits has allowed crows and ravens to “take over the world.” Their wing size allowed them to travel far distances and colonize across the world, but they likely would not have survived without the other traits.

“Really big relative brain size in birds is an indication that they had better cognitive abilities,” Botero said. This enhanced problem-solving capability could contribute to the animals’ behavioral flexibility. “They’re able to adjust how they interact with other species, where they nest, what they eat. That flexibility allows them to be really great at surviving.”

Their large size made them competitive against other birds already existing in the habitat, according to Botero.

“Once they arrived at a new spot, their bodies were not perfectly adapted, but they were still able to survive,” Botero said. “By surviving in those places over thousands, potentially millions of years, their bodies started to change through evolution and adapt into forms that were better suited for a particular habitat.”

Crows are known to be extremely intelligent, using tools and solving complex abstract problems. Botero said this makes them ideal for future research on the “ecology of cognition.”

“What benefits does it give you to have a big brain like the crow’s brain and like our brain? What are the advantages, what are the costs and how that relates to other important things in life like how you interact with other species, how you produce the species eventually or how you survive in this world?” Botero said. “Those are the kinds of open questions that my lab and my crew are deep in thinking trying to address.”

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