Crows and ravens diversified both quickly and widely because they were particularly good at coping with different habitats.
You know them because you see them in your neighborhood every day. And you certainly have heard their distinctive, harsh caws and kraas.
They are crows and ravens, the corvids that are well-known for their black color. Crows can be found all over the world in a variety of habitats. For example, the American crow lives throughout North America, preferring open areas—agricultural land and grasslands—with trees nearby. They also thrive in suburban neighborhoods, according to the University of Michigan’s Animal Diversity Web (ADW).
Ravens, too, are one of the most widespread birds worldwide. They are found in northern Europe; Greenland; Iceland; Scandinavia; throughout Asia, from the Pacific Ocean to the Himalayas to India and Iran; across northwestern Africa and the Canary Islands; and in North and Central America as far south as Nicaragua. Like crows, they prefer open landscapes: deserts, mountain forests with meadows, plains, open riverbanks, rocky cliffs, scrubby woodlands, seacoasts and treeless tundras.
These maps show the extent of modern-day crows and ravens, shown in red, as compared with other members of the family “Corvidae.” ©Botero Lab and “Nature Communications”
Crows and ravens are extremely intelligent birds that can solve complex, abstract problems. They use tools. They speak a volume of “words”; for example, common ravens have 15 to 33 categories of recorded vocalizations. When a crow encounters a mean human, it will teach other crows how to identify that human. In fact, research shows that crows don’t forget a face.
But is intelligence the only reason for their rapid global expansion, unlike their other family members (such as jays and magpies) that stayed mostly within single continents? Just what is the secret to their amazing planetary expansion?
Bodacious bodies and bigger brains
Crows and ravens have an advanced flying ability, which allows them to gain access to new places more easily. But while their flying skills were key to their success, new research from Washington University in St. Louis, Missouri, published in Nature Communications in April 2022, shows that big bodies and big brains also played important roles in helping crows and ravens survive in the new climates they came to occupy.
Longer wing lengths are just one of the traits that helped crows and ravens to colonize the world. ©Tim Spouge, flickr
In the Nature Communications study, the authors show that crows’ and ravens’ incredible ability to rapidly expand and diversify across the planet was driven by a specific combination of traits.
Using specimens housed in museums across Europe and the U.S., scientists found that crows and ravens have longer wing lengths, bigger body sizes and bigger relative brain sizes compared to other corvids.
Longer wings means a better flying capacity, which allowed the birds to disperse across the world. Their bigger body sizes gave them a competitive advantage over smaller species, helping them establish in new places. And their big brains relative to their body sizes suggest that ancestral crows and ravens were behaviorally flexible. They were smarter than other corvids and, therefore, able to figure out how to live in new environments, increasing their chances of survival.
As they adapted to the many different environments they encountered as they spread across the planet, crows and ravens acquired new beak shapes that did not exist in any other corvid.
These new insights from this research reveal how crows and ravens were able to do things that even close relatives could not. 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.
New homes and novel looks
Crows and ravens experienced high rates of trait evolution and speciation as they adapted to the many different environments they encountered during their rapid expansion across the planet. In fact, they had the highest rates compared with any other member of the family Corvidae.
Arrival in a new environment exposed them to new selective pressures. New environments often favor tweaks to an organism’s phenotype that facilitate survival and overall performance. That process is known as “optimizing selection,” with the potential to create new species. For example, crows’ and ravens’ ability to live in the cold Arctic after moving from a tropical rain forest likely required very different strategies and traits.
A group of ravens is called an “unkindness.” A group of crows is known as a “murder”—which brings up an interesting fact. When one crow dies, the murder will surround the deceased. This funeral isn’t just to mourn the dead, though. The crows gather to find out what killed their companion. Then, the murder will chase the predator in a behavior called “mobbing.”
For crows and ravens, that meant acquiring new beak shapes that did not exist in any other corvid, thereby increasing beak shape variation in the Corvidae family. The scientists also found that crows and ravens increased body size variation as they colonized new environments.
Clever conservationists and convenient consumers
When we think about wildlife and their processes of global diversification, it is important to consider not just the ability to reach new places, but also the aptitude for surviving once you get there. Thanks to these two amazing corvids, we now understand a bit more about how animals can rapidly expand across the planet and how this geographic expansion can translate into the creation of new species with new morphologies.
But I’m not only thankful to crows and ravens for that. I think of these corvids as the common conservators of our world. In one nesting season, a crow family can eat 40,000 armyworms, caterpillars and grubs—insects that many farmers and gardeners consider to be pests. These winged environmentalists also transport and store seeds, thus contributing to forest renewal.
Crows and ravens are important in fables, mythology and native cultures. They are often identified as clever tricksters. I say that they are clever conservationists.
In addition, crows and ravens provide critical sanitation services by eating animals that have died either by natural causes or because they were hit by vehicles. And it’s not just the benefits of clean roads and stench-free air that make scavengers such as these birds so important. They prevent diseases, too.
Feral dogs or rats might take days to discover a carcass. But crows and ravens can arrive within an hour of an animal’s death; and in flocks (which, in the case of crows is called a murder; and for ravens, an unkindness), they can quickly leave nothing behind but clean bones. Without these birds’ efficiency, harmful bacteria, flies carrying illnesses, and diseases such as rabies and tuberculosis would inevitably spread.
And, along with their superior intelligence, their invaluable environmental benefits and their critical sanitation services, they’re always up for a little fun.
Who couldn’t love that?
Here’s to finding your true places and natural habitats,
Candy
