New Caledonian crows have acquired the ability to make and use tools thanks to an unusually straight beak and canceled the binocular vision, say British biologists in a paper published in the journal Nature Communications.
It is believed that most of the birds of the genus of crows have remarkable mental abilities. They often outperform many other mammals and birds in tests of intelligence. Most ornithologists believe New Caledonian crows (Corvus moneduloides) champions in the field. These birds, along with a man and some higher primates, part of the "elite club" of animals, able to make and use tools.
Team of biologists led by Christian Ratz (Christian Rutz) from Oxford University (UK) tried to find the cause of the evolutionary development of such abilities in crows, comparing their anatomical arrangement with other members of the genus Corvus.
The work Ratz and his colleagues turned their attention to two main "tool" in the manufacture and use of tools — "visual sensor" as the eyes and the "manipulator"-beak. Biologists have compared the structure of the eye, and the breadth of the field of binocular vision, as well as the shape of the beak in New Caledonian crows and their immediate families in the face of common ravens, rooks, jackdaws, piebald ravens (Corvus albus) and black crows (Corvus corone).
It was found that New Caledonian crows have the widest field of binocular vision, not only among his relatives, but most of the other birds. According to biologists, the field of vision of the left eye and right eye Corvus moneduloides intersect at 60 degrees, which is about 10 degrees higher than the maximum rates for other birds with good binocular vision.
Scientists checked, does binocular vision bird on its ability to use tools. To do this, scientists put the infrared camera in the trunk of the artificial "trees", where the food was hidden, and trace the location and movement of the eyes of their wards, extracting food from the cache.
Binocular vision has been one of the key tools for working with tools. According to scientists, the birds tried to look inside the "dead drop" two eyes, trying to achieve maximum clarity and "depth" pictures. Using a stick or other tools, Corvus moneduloides kept it in the tip of the beak, holding the tool in binocular "sector" view.
Special, unusual "flat" beak became the second key factor in allowing the New Caledonian crows use tools. According to scientists, this form of the beak allows Corvus moneduloides hold sticks and other tools as parallel beak, and a wider angle.
According to biologists, "slanted" tools are better suited to extract food from narrow holes than the sticks that would keep birds beak in parallel, as they do not obstruct the field of view of the outsider. Other members of the genus Corvus have curved beak, which does not allow them to keep the tools within the area of stereoscopic vision.
As the Ratz and his colleagues, it is not clear whether these features Corvus moneduloides cause or a consequence of their unique abilities. However, the study of other differences, the New Caledonian crows from their closest relatives may be the key to understanding how to develop similar skills in man and his immediate ancestors, biologists concluded.