To recognize a movement and choose a response, some crows acted almost twice as fast as humans.
Two carrion crows took part in an experiment conducted at the University of Tübingen, Germany. In front of them, a screen displayed white dots moving in different directions. The birds had to decide whether most of the dots were moving to the left or to the right, then peck the correct location on the screen.
Carrion crow lifting grass to search for worms in the Jardin des plantes, Paris.
Photo: Wikimedia Commons, via Wikimedia Commons. Detailed license and attribution information is available on the file page.
The crows made their decision in an average of 235 milliseconds. That is less than a quarter of a second and about twice as fast as the time recorded in humans and other primates during comparable tasks. The birds also responded with great accuracy when the movement was easy to recognize.
But the researchers did more than time the responses. They recorded the activity of nerve cells in a region of the crows' brains involved in decision-making. They wanted to understand how information was processed even before the bird moved its beak.
The first differences appeared about 70 milliseconds after the images arrived. Some nerve cells were already responding differently depending on the direction of the dots. Their activity then evolved gradually, until the crow seemed to have enough information to make its choice.
This process resembles what scientists observe in the brains of primates. Yet birds' brains are not built like ours. They do not have the same layered organization at the surface. That does not prevent them from using mechanisms that lead to comparable decisions.
Why such speed? The researchers point to the needs of birds in the wild. In flight, they must react to obstacles in a fraction of a second. To catch food with their beaks, they also need to coordinate their eyes and movements precisely.
It would nevertheless be wrong to conclude that crows think twice as fast as we do in every situation. Only two birds were tested here, using a specific task. The result measures neither their general intelligence nor their ability to solve just any problem.
The study mainly shows that a brain very different from ours can analyze certain information with astonishing speed. The researchers now want to understand what enables birds' nerve cells to make a decision so quickly.