Strong Evidence for “Speciation Reversal” Phenomenon Found Through Ravens

An important finding for the study of animal history worldwide, all the better that it’s shown through wonderful corvids.


For over a century, speciation — where one species splits into two — has been a central focus of evolutionary research. But a new study almost 20 years in the making suggests “speciation reversal” — where two distinct lineages hybridize and eventually merge into one — can also be extremely important. The paper, appearing March 2 in Nature Communications, provides some of the strongest evidence yet of the phenomenon, in two lineages of Common Ravens.

“The bottom line is [speciation reversal] is a natural evolutionary process, and it’s probably happened in hundreds or almost certainly thousands of lineages all over the planet,” said Kevin Omland, professor of biological sciences at University of Maryland, Baltimore County (UMBC) and co-author on the new study. “One of our biggest goals is to just have people aware of this process, so when they see interesting patterns in their data, they won’t say, ‘That must be a mistake,’ or, ‘That’s too complicated to be correct.'”

“We examined genomic data from hundreds of ravens collected across North America,” said Anna Kearns, the study’s first author and a former postdoctoral fellow at UMBC, who is now a postdoc at the Smithsonian Center for Conservation Genomics. “Integrating all of the results across so many individuals, and from such diverse datasets, has been one of the most challenging aspects of this study. Next-generation genomic techniques are revealing more and more examples of species with hybrid genomes.”


The best explanation based on the team’s analysis is that the California and Holarctic lineages diverged for between one and two million years, but now have come back together and have been hybridizing for at least tens of thousands of years.

“The extensive genetic data reveals one of the best supported examples of speciation reversal of deeply diverged lineages to date,” said Arild Johnsen, professor of zoology and evolutionary biology at University of Oslo and another leader of the study. “The biggest thing is the degree to which we’ve caught them in the act.”

How does this relate to people? Humans are also a product of speciation reversal, Omland notes, with the present-day human genome including significant chunks of genetic material from Neanderthals and Denisovans, another less well-known hominid lineage. Recent genetic studies have even indicated a mysterious fourth group of early humans who also left some DNA in our genomes.

“Because speciation reversal is a big part of our own history,” Omland said, “getting a better understanding of how that happens should give us a better sense of who we are and where we came from. These are existential questions, but they are also medically relevant as well.”


Co-author John Marzluff, professor of wildlife science at the University of Washington, summed up the experience of being part of the study: “It is fascinating to me that this complex history of raven speciation has been revealed. For decades my students and I held and studied ravens throughout the West and never once suspected they carried evidence of a complex past,” he said. “Thanks to collaborations among field workers and geneticists, we now understand that the raven is anything but common.”

Wonderful Facts About Ravens and Crows

This article has a nice compilation on the wonders of corvids. Additional h/t to — the corvid research shown there has been valuable.


We’re sure you have your favourite animal. It may even be a really smart one. But corvids – such as crows, magpies and ravens – really are something special. In fact, they’re some of the most intelligent animals in the world.

And here we’ve gathered some of the finest examples of just how clever these gorgeous creatures can be.


In an experiment with tubes published in PLOS One, scientists determined that New Caledonian crows can not only tell the difference between water and sand – they also understand water displacement.

The test involved tubes containing water and a treat floating on top out of reach. The crows filled the tubes with enough rocks or other heavy items to bring the food within reach.


Ever wonder why crow researchers sometimes wear masks? It’s because crows can recognise human faces, especially the faces of humans who have done them wrong.

So, if you’re trying to record how crows react to negative stimuli (such as being caught and tagged), you don’t want to do that using your real face. If you do, you’ll get loudly scolded by the agitated flock every time you approach, as biologist John Marzluff discovered and detailed in a 2011 paper.

Good thing he did, too. A few years later, he found out that crows not only hold onto that grudge – they tell other crows about it, too.

Within the first two weeks after trapping, around 26 percent of crows scolded the human wearing the danger mask. Around 15 months later, that figure was 30.4 percent.

Three years after the initial trapping event, with no action towards the crows since, the number of scolding crows had grown to 66 percent.


When a crow dies, other crows are often observed gathering around and making a lot of loud noise – much like humans, really. The reason for this was unknown until 2015, when crow researcher Kaeli Swift crowdfunded research to try and figure out why.

Her conclusion, published in the journal Animal Behaviour, was that crows gather around their dead fellows to learn about danger.

And it works. The city of Chatham, Ontario is beneath a crow migration route, and they plague the town on their way through. Every attempt to get rid of them has failed – including shooting at them with pellet guns. The crows learnt how to fly just high enough to evade the fire.


6. Crows can solve complex, multi-step puzzles

This crazy impressive experiment was conducted as part of a BBC Two program called Inside the Animal Mind, putting crows to the test with the most complex animal puzzle ever.

And not lab crows, either. The crows were captured from the wild one at a time, and kept for just three months.


In 2015, researchers announced they had filmed the first ever video evidence of crows fashioning tools in the wild using a specially developed spy camera mounted on the crows’ tail feathers.

They were observed snapping twigs from trees, then stripping it of bark and leaves, and fashioned the node into a hook. They then used these tools to probe into small spaces for food.

“The behaviour is easy to miss – the first time I watched the footage, I didn’t see anything particularly interesting. Only when I went through it again frame-by-frame, I discovered this fascinating behaviour. Not once, but twice!” researcher Jolyon Troscianko said.

“In one scene, a crow drops its tool, and then recovers it from the ground shortly afterwards, suggesting they value their tools and don’t simply discard them after a single use.”


In a 2015 study, researchers from the University of Vienna gave ravens a task wherein they would only receive the reward if they cooperated, pulling on ropes to raise a platform which had two pieces of cheese, one for each raven.

If one raven stole their companion’s cheese, as well as their own, they were on the outs: the other raven would refuse to cooperate with them – but they would cooperate with other ravens who played fair.

“Such a sophisticated way of keeping your partner in check has previously only been shown in humans and chimpanzees, and is a complete novelty among birds,” lead researcher Jorg Massen said.


9. Crows can exercise self control

Crows aren’t driven purely by instinct – they can experience anticipation, and exercise self-control if the end result is a greater reward.

2014 study devised a test based on the Stanford marshmallow experiment, a 1960s study into delayed gratification in children. The first step was to determine which snacks the crows liked the most. The researchers fed them grapes, bread, sausage, fried fat and other treats.

Next, they were given a snack and the option to trade their snack – if they were willing to wait. They could either receive a better quality snack – meat in exchange for a grape, for instance – or a higher quantity of the same snack.

The birds preferred to wait until a better snack was on offer, but if it was just more of the same, they weren’t. In some cases, they waited up to 10 minutes for a better snack. The fact that they waited for better quality, not quantity, showed that they were waiting because they wanted to – not because they were actually hungry.


11. Ravens remember people who have been nice to them

You know how crows hold a grudge? Well, corvids also remember people who have been nice to them. There was, of course, that adorable case of a little girl who crows started bringing shiny objects to after she regularly fed them – but there’s been a scientific study on the subject too.

Again, it involves ravens trading a low-quality snack (bread) for a high-quality snack (cheese), which they’d been trained to do. Then two humans brought the cheese to trade for the bread. One experimenter would fairly give the cheese when the crow handed over the bread. The other experimenter ate the cheese themselves after being given the bread.

Then, after an interval – two days, and then later one month – three humans entered the enclosure, the fair one, the unfair one, and a neutral control. The raven was given a piece of bread to trade. Most of the ravens chose to trade with the fair experimenter – indicating that they remembered being cheated out of delicious cheese and weren’t falling for that again.