Crows have a reasoning ability rivalling that of a human seven-year-old, research has shown.
Scientists came to the conclusion after subjecting six wild New Caledonian crows to a battery of tests designed to challenge their understanding of cause and effect.
The tasks were all variations of the Aesop’s fable in which a thirsty crow drops stones to raise the level of water in a pitcher.
They selected objects that sank rather than floated, and were solid rather than hollow, to raise the food high enough for them to reach.
In the ‘water displacement task’, crows worked out how to catch floating food rewards by dropping heavy objects into water-filled tubes.
They demonstrated an ability to drop sinking rather than floating objects, solid rather than hollow objects, to choose a high water level tube over one with low water level, and a water-filled tube over one filled with sand.
The crows failed on two more difficult tasks, however. One test required understanding of the width of the tube and the other involved displacing water in a U-shaped tube.
Nevertheless, the birds’ understanding of the effects of volume displacement matched that of human children aged between five and seven, claimed the scientists.
Researchers at the University of Auckland in New Zealand say the bird’s understanding of the task matched that of human children aged five to seven.
Sarah Jelbert, lead researcher, said: “These results are striking as they highlight both the strengths and limits of the crows’ understanding. In particular, the crows all failed a task which violated normal causal rules, but they could pass the other tasks, which suggests they were using some level of causal understanding when they were successful.”
New Caledonian crows, named after the Pacific islands where they live, are famous for their intelligence and inventiveness.
They are the only non-primate species to make tools, such as prodding sticks and hooks, to winkle out grubs from logs and branches.
Another recent study also seemed to support the problem-solving ability of the birds.
The experiment, which was devised by Dr Alex Taylor, a Lecturer in Evolutionary Psychology based at The University of Auckland, New Zealand, involved a wild crow which had learned to use individual props during three months of captivity.
It successfully managed to work out the order in which to use them to complete an eight stage puzzle in approximately two-and-a-half minutes and get an inaccessible treat. The animal was later released.
The findings appear in the latest issue of the online journal PLOS ONE.