A study led by researchers at Lund University in Sweden shows that
ravens1 are as clever as chimpanzees, despite having much smaller brains, indicating that rather than the size of the brain, the neuronal
density2 and the structure of the birds' brains play an important role in terms of their intelligence. "Absolute brain size is not the whole story. We found that corvid birds performed as well as great apes, despite having much smaller brains", says Can Kabadayi, doctoral student in
Cognitive3 Science.
Intelligence is difficult to test, but one aspect of being clever is inhibitory control, and the ability to
override4 animal impulses and choose a more rational behaviour. Researchers at Duke University, USA, conducted a large-scale study in 2014, where they compared the inhibitory control of 36 different animal species, mainly
primates5 and apes. The team used the established
cylinder6 test, where food is placed in a
transparent7 tube with openings on both sides. The challenge for the animal is to
retrieve8 the food using the side openings, instead of trying to reach for it directly. To succeed, the animal has to show
constraint9 and choose a more efficient strategy for obtaining the food.
The large-scale study concluded that great apes performed the best, and that absolute brain size appeared to be key when it comes to intelligence. However, they didn't conduct the cylinder test on corvid birds.
Can Kabadayi, together with researchers from the University of
Oxford10, UK and the Max Planck Institute for
Ornithology11 in Germany, therefore had ravens, jackdaws and New Caledonian crows perform the same cylinder test to better understand their inhibitory control.
The team first trained the birds to obtain a treat in an
opaque12 tube with a hole at each end. Then they repeated the test with a transparent tube. The animal impulse would naturally be to go straight for the tube as they saw the food. However, all of the ravens chose to enter the tube from the ends in every try. The performance of the jackdaws and the crows came very close to 100%, comparable to a performance by bonobos and
gorillas13.