Article image

Big brains and bodies helped crows expand across the globe

Crows and ravens are intelligent birds that use tools, solve complex problems and are known for their vocal “caw” sounds. 

What is less well appreciated is their diversity and ability to live all over the world in a variety of habitats. They are one of the most widespread groups of birds worldwide. This is because crows and ravens – part of the avian family of Corvids – underwent rapid global expansion, unlike other birds that stayed within single continents.

Their planetary exploration is largely due to their great flying ability, which allows them to access new places more easily. 

New research also shows that their big bodies and brains played an important role in surviving in the new climates they occupied.

“When we think about processes of global diversification, it is important to consider not just the ability to reach new places, but also the ability to survive once you get there. Our work suggests that crows and the ravens diversified both quickly and widely because they were particularly good at coping with different habitats,” said Carlos Botero, assistant professor of biology in Arts & Sciences at Washington University in St. Louis.

The researchers show that the birds’ ability to rapidly expand and diversify across the planet was driven by a combination of traits. Using specimens housed in museums, the scientists found that these birds have longer wing lengths, bigger body sizes and bigger relative brain sizes compared with other Corvids.

“We hypothesize that these three very convenient combinations of traits are what allowed this group of birds to colonize and diversify across the world,” said study first author Joan Garcia-Porta.

Three convenient traits:

  1. Longer wings gave crows and ravens higher flying capacities, which allowed the birds to travel across the world. 
  2. Big brains suggest that ancestral crows and ravens were behaviorally flexible. They were smarter than other Corvids and able to figure out how to live in a new environment and increase their chances of survival. 
  3. Bigger body size gave crows and ravens a competitive advantage over smaller species, helping them establish in a new place.

“We are excited with these new insights on how these birds were able to do things that even close relatives did not,” said Professor Botero. “It truly seems that their incredible behavioral flexibility may have played a major role in allowing these birds to survive initial periods of maladaptation and hang in there long enough for selection to catch up and produce a range of new species in the process.”

Traveling across the world required crows and ravens to adapt to many different environments and resulted in high rates of evolution and speciation. This is because arriving in a new environment comes with exposure to selective pressures. For example, living in the cold Arctic after moving from a tropical rainforest likely required very different strategies.

“These new environments often favor tweaks to an organism’s phenotype that facilitate survival and overall performance. That process is often known as optimizing selection,” said Professor Botero.

This caused crows and ravens to acquire new beak shapes that did not exist in any other Corvid, increasing beak shape variation in the Corvidae family. The scientists also found that the birds increased body size variation as they colonized new environments.

“Thanks to these amazing birds, we now understand a bit more the processes by which animals rapidly expand across the planet and how this geographic expansion translates to the production of new species with new morphologies.” Concluded Garcia-Porta.

The study is published in the journal Nature Communications.

By Katherine Bucko, Staff Writer

News coming your way
The biggest news about our planet delivered to you each day