Crows may be as intelligent as a child of seven years old, according to new research. The birds have even solved some of Aesop's famous puzzles.
The study was carried out on crows from New Caledonia, a collection of islands 750 miles east of Australia. Six individuals of Corvus moneduloides from the island of Grande-Terre were captured for the experiment.
The Crow and the Pitcher inspired this experiment. In this story, a thirsty crow finds a pitcher containing water that is too low in the container for the bird to reach. The clever avian begins to drop small stones in the vessel, until it is able to quench its thirst.
Study of the bird involved a vessel containing a treat and water. A small piece of meat, floating on a cork, is out of reach. By placing pebbles into a container, the birds were able to raise the water level, making the treat accessible. This test was meant to access the ability of the avian to understand the basics of fluid dynamics.
"We found that crows preferentially dropped stones into a water-filled tube instead of a sand-filled tube; they dropped sinking objects rather than floating objects; solid objects rather than hollow objects, and they dropped objects into a tube with a high water level rather than a low one, researchers wrote in the article announcing their study.
When made to choose between a vessel with water at the bottom and one containing sand, 76 percent of all stones drops were made in the water-filled container. Researchers also gave the birds a choice between polystyrene (which floats) or rubber "stones" which sinks. Hollow and solid objects were made available to the birds being tested. In 90 percent of these cases, the crows made the correct choice. This is the first time crows have ever been shown to understand the notion that hollow items are more likely to float, and that this will not raise the water level.
Crows failed more advanced tests, involving tubes of different widths and U-shaped vessels. This suggests a rudimentary, yet incomplete, knowledge of the notion of displacement. Researchers suggest the level of understanding crows possess may rival that of children between the ages of five and seven.
Corvus moneduloides is the only non-mammal known to create and use tools in the wild. The birds tear barbed leaves off twigs, and use the objects as hooks to capture insects. In captivity, they adapt to bending wire for use in retrieving food.
Sarah Jelbert of the University of Auckland led the research.
"Understanding this could in turn help us to piece together the evolution of cognition in our own species," Jelbert told the press.
An article profiling the study into the intelligence of crows was published in the online journal PloS One.
