Whether crows, ravens, and other "corvids" are making multipart tools like hooked sticks to reach grubs, solving geometry puzzles made famous by Aesop, or nudging a clueless hedgehog across a highway before it becomes roadkill, they have long impressed scientists with their intelligence and creativity.
Now the birds can add one more feather to their brainiac claims: Research unveiled on Thursday in Science finds that crows know what they know and can ponder the content of their own minds, a manifestation of higher intelligence and analytical thought long believed the sole province of humans and a few other higher mammals.
A second study, also in Science, looked in unprecedented detail at the neuroanatomy of pigeons and barn owls, finding hints to the basis of their intelligence that likely applies to corvids’, too.
"Together, the two papers show that intelligence/consciousness are grounded in connectivity and activity patterns of neurons" in the most neuron-dense part of the bird brain, called the pallium, neurobiologist Suzana Herculano-Houzel of Vanderbilt University, who wrote an analysis of the studies for Science, told STAT. "Brains can appear diverse, and at the same time share profound similarities. The extent to which similar properties present themselves might be simply a matter of scale: how many neurons are available to work."
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Understanding the minds of nonhuman animals promises to shed light on the origins of such cognitive abilities as, in this case, knowing and analyzing the contents of one’s own brain. That’s how people solve challenges and make discoveries — what do I know? what if I look at it this way? — and it’s a pillar of higher intelligence. Knowing what you know is also a form of consciousness, and the discovery that more and more nonhumans seem to have it raises tricky questions about how we treat them.
"It has been a good week for bird brains!" said crow expert John Marzluff of the University of Washington, who was not involved in the new studies. In particular, the discovery that crows know what they know will not surprise avian scientists, "who have increasingly demonstrated the cognitive abilities of birds, … but they will be relieved! This research is groundbreaking."
To test whether crows know and can analyze the contents of their brains, neurobiologist Andreas Nieder of the University of Tübingen in Germany trained two birds to peck a red or a blue target on a panel, depending whether they saw a faint light. Nieder kept varying the "rule," with the birds told which color meant what — red = saw it, or blue = saw it — only after the flash. That required the crows, Glenn and Ozzy, to keep monitoring their brains; they had a second or two to figure out what they had seen and tell Nieder by choosing the corresponding target.
While the crows were solving these tasks, the researchers were tracking the activity of hundreds of their neurons. (Crows’ brains have 1.5 billion neurons, as many as some monkey species.)
When the crows reported having seen a faint light, sensory neurons were active between the flash and the birds pecking the color that meant, yes, I saw that. If the crows did not perceive the very same faint stimulus, the nerve cells remained silent, and the bird pecked, no, I didn’t see anything. Ozzy and Glenn’s brain activity systematically changed depending on whether or not they had perceived the dim flash.
During the delay, many neurons responded according to the crows’ impending report, rather than to the brightness of the light. "A population of neurons contained information about the crows’ subjective experience throughout the trial," the scientists wrote.
The birds were aware of what they subjectively perceived, flash or no flash, correctly reporting what their sensory neurons recorded, Nieder told STAT. "I think it demonstrates convincingly that crows and probably other advanced birds have sensory awareness, in the sense that they have specific subjective experiences that they can communicate," he said. "Besides crows, this kind of neurobiological evidence for sensory consciousness only exists in humans and macaque monkeys."
The study shows that neurons in the most complex part of the crows’ brain, the pallium, "do have activity that represents not what was shown to them, but what they later report," said Herculano-Houzel. Neurons "represent what the animals next report to have seen — whether or not that is what they were shown," she said. The neurons figure this out, so to speak, during the time lapse between when Nieder tells the birds the rule and when they peck the target to indicate their answer.
"That’s exactly what one would expect from neurons that participated in building the thoughts that we later report," she said, suggesting that corvids "are as cognitively capable as monkeys and even great apes."
A second study looked in unprecedented detail at the neuroanatomy of pigeons and barn owls, finding hints to the basis of their intelligence that likely applies to corvids’, too. Scientists have long known that crows and ravens have unusually large forebrains, but unlike mammals’ forebrains — the neocortex — corvids’ do not have the six connected layers thought to produce higher intelligence. But theirs do have "connectivity patterns … reminiscent of the neocortex," scientists led by Martin Stacho of Ruhr-University in Germany reported.
Specifically, the pigeons’ and owls’ neurons meet at right angles, forming computational circuits organized in columns. "The avian version of this connectivity blueprint could conceivably generate computational properties reminiscent of the [mammalian] neocortex," they write. "[S]imilar microcircuits … achieve largely identical cognitive outcomes from seemingly vastly different forebrains." That is, evolution invented connected, circuit-laden brain structure at least twice.
"In theory, any brain that has a large number of neurons connected into associative circuitry … could be expected to add flexibility and complexity to behavior," said Herculano-Houzel. "That is my favorite operational definition of intelligence: behavioral flexibility."
That enables pigeons to home, count, and be as trainable as monkeys. But for sheer smarts we’re still in the corvid camp. A 2014 study showed that New Caledonian crows, rooks, and European jays can solve an Aesop’s Fable challenge, dropping stones into a water-filled tube to bring a floating bit of food within reach, something kids generally can’t do until age 7. These birds were the first nonhuman animals to solve the task.