Clever crows are as bright as children
Crows have the reasoning ability of a seven-year-old child, new research suggests.
Scientists challenged New Caledonian crows with variations of the Aesop's Fable The Crow and the Pitcher, in which a thirsty bird dropped stones into a jug to raise the level of water.
The six crows in the study worked out how to obtain floating food rewards by dropping objects into water-filled tubes.
They selected objects that sank rather than floated, and were solid rather than hollow, to raise the food high enough for them to reach.
But they failed on two more difficult tasks, including one that required them to displace water in a U-shaped tube, according to results published in the scientific journal PLOS ONE.
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.