How exactly do you measure how smart an animal is? Assessing the intelligence of an animal is a difficult task in itself, and it remains a controversial subject. Researchers at Lund University may not be able to answer the enormity of the question, but by using a simple test, they have been able to assess corvid intelligence, and demonstrate that they may be among the cleverest in the animal kingdom.

Scientists have developed various methods over the years to try and determine an animals’ intelligence. One such test is known as the ‘cylinder test’. Designed to assess an animal’s ability to override its gut instinct and choose a more rational behaviour, the cylinder test is accepted within the scientific community as a good predictor of intelligence. It is both simple and clever, consisting of food placed inside a transparent cylinder, with openings on either side.

The challenge for the test subject is to retrieve the food using the openings, rather than trying to reach for it directly. The idea being that for the animal to be successful, it must override its natural instinct to go straight for the delicious, tempting morsel of food it is faced with, and instead use the side openings to achieve its goal. This kind of response is known as inhibitory control.

In 2014, researchers at Duke University used this test as a basis for a large scale study in which they looked at the inhibitory control of 36 different animal species. They found that it was the great apes, such as chimpanzees and gorillas, that performed the best and that absolute brain size was a key determinant of intelligence.

However, one key group of animals was overlooked. Corvids, the family of birds that includes crows, ravens, and jackdaws. Despite already being well known for their problem-solving and cunning, they were not included in the original study.

Can Kabadayi from Lund University recently rectified that, had his group of corvids perform the same task, and compared the results to those of the great apes. The birds were trained to retrieve food from an opaque tube using the holes at either end, before then being tested with a transparent tube. With the food in sight, you might at first expect the birds to make a grab for the tantalising treat directly, which would of course only result in an abrupt stop for the bird’s beak, and a failure of the test. However, all of the ravens tested, along with almost all of the crows and jackdaws, chose to enter the tube from the openings at the end. This kind of performance is comparable to those of both the bonobo and gorilla, despite the birds much smaller brain.

“This shows that bird brains are quite efficient, despite having a smaller absolute brain size. As indicated by the study, there might be other factors apart from absolute brain size that are important for intelligence, such as neuronal density,” says lead author Can Kabadayi. “There is still so much we need to understand and learn about the relationship between intelligence and brain size, as well as the structure of a bird’s brain, but this study clearly shows that bird brains are not simply birdbrains after all!”

Can Kabadayi discusses his research into corvid intelligence.

This is not the first time that this group of birds have been shown to be intelligent though. They have been taught to complete tasks using tools in order to obtain food and have even been shown to understand water displacement.

Example trials of crows during water displacement experiments. Jelbert SA, Taylor AH, Cheke LG, Clayton NS, Gray RD (2014) Using the Aesop’s Fable Paradigm to Investigate Causal Understanding of Water Displacement by New Caledonian Crows. PLoS ONE 9(3): e92895. doi:10.1371/journal.pone.0092895.


Can Kabadayi, Lucy A. Taylor, Auguste M. P. von Bayern, Mathias Osvath. Ravens, New Caledonian crows and jackdaws parallel great apes in motor self-regulation despite smaller brains. Royal Society Open Science, 2016; 3 (4): 160104 DOI: 10.1098/rsos.160104


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