Two Crows Took a Test Built for Humans and Monkeys. They Answered in 235 Milliseconds

It turns out a so-called birdbrain can make a choice extremely quickly. In a new study, two carrion crows beat humans and monkeys on a classic visual decision task, and scientists also tracked the brain activity behind those fast calls.

A lab test that usually belongs to primates

The experiment focused on a well known psychology task used to study perceptual decision-making. Each crow stood in front of a touch-sensitive screen showing many dots. Some of those dots moved either left or right, and the bird had to peck the matching side of the screen to show which way it thought the motion was going.

A correct answer brought a mealworm reward. The task was self-paced, with a wide window for the birds to respond, because the idea was to capture the moment they felt confident enough to commit to a choice rather than push them to answer as fast as possible.

This random-dot motion discrimination task has been used before with humans and monkeys, but not with crows. Before the real data were gathered, both adult male carrion crows were trained across more than 100 sessions each so the researchers could be sure they understood what to do.

When the scientists measured the birds' performance, the result stood out. The crows reported their choices in about 235 milliseconds on average. The researchers said that was roughly twice as fast as what has been observed in monkeys or humans doing comparable tasks. Just as striking, that extra speed did not come with a drop in accuracy.

Why researchers find crow intelligence so intriguing

Crows are part of the corvid family, a group that also includes ravens, rooks, jackdaws and jays. Corvids have already built a strong reputation in animal cognition research.

Previous studies have found that New Caledonian crows can make compound tools and plan three steps ahead. Western scrub jays have shown episodic-like memories. Ravens have displayed behaviour researchers have described as smart enough to be paranoid. The new work adds another piece to that picture by showing extremely fast visual decision-making in carrion crows.

For the scientists behind the study, the point is not simply to add another clever feat to the list. They want to know how birds pull off this kind of mental performance with brains that are built very differently from mammalian brains.

Birds do not have a layered cerebral cortex, the structure often treated as the mammalian brain's highest integration centre. Andreas Nieder has previously explained that bird brains instead rely on circuits that come from a different part of the pallium. He has also argued that although bird brains are smaller than ours, their neurons are smaller too. That means information has less distance to travel, and more processing can be packed into the same amount of space. By his account, a corvid brain can hold about twice as many neurons as a primate brain of equal mass.

What the birds' brains were doing before each peck

To look past behaviour and into the actual decision process, the researchers implanted electrodes into the crows' brains. The recordings targeted the nidopallium caudolaterale, or NCL, an area that contains neurons involved in perceiving motion direction such as the left or right drift of the dots on the screen.

On waking from surgery, the birds performed the same task again while the team recorded activity from 248 individual neurons. Those brain signals revealed that the crows were not making random fast guesses.

According to the study, neurons linked to the birds' upcoming decisions began firing about 70 milliseconds after the dots started moving. That activity appeared around 170 milliseconds before the peck that counted as the final answer.

The researchers said the findings suggest crows show primate-like decision computations even though their neural architecture is distinct. In other words, the birds may be reaching a similar end point through a different brain design, and doing it with markedly greater temporal efficiency.

A small study with a big curiosity factor

Nieder said one possible reason for such speed is the kind of challenges birds face. They rely on vision to carry out precise, rapid manoeuvres during flight and to guide their beaks toward objects while foraging. Fast visual decisions would fit that way of life.

There is a major limitation, though. The study included only two crows, which is far too small a sample to say how representative the result is for carrion crows in general. The work is best seen as an early step rather than a final verdict on the species.

Even with that caveat, the study offers a striking example of how much computing power can sit inside a very different kind of brain. A test long used to probe human and monkey decision-making ended up showing that two crows could make the same kind of call faster than either of them.

The research was carried out by Philipp Schmidbauer and Andreas Nieder of the University of Tübingen in Germany and published in Science.