String Pulling In New Caledonian Crows

In my chapter CLEVER CORVIDS I mention research on the ability of ravens to pull appropriately on strings in order to haul up a piece of food. The fact that the birds seemed to successfully pass this test very quickly suggested they might be using some level of insight into the problem. The lower-order cognitive explanation, however, might involve visual feedback whereby the bird can monitor the food as it ascends in stages with each beak-pull and foot-secure action on the string. So each pull brings the food closer and reinforces subsequent pulls on the rope. This research switches the test to New Caledonian crows and comes from the New Zealand stable of Gavin Hunt and Russell Gray. The performance of even birds experienced on the task fell off when vision of the ascending food was excluded, suggesting they were employing the lower-level cognition. Here is the abstract to this free access paper:

The ability of some bird species to pull up meat hung on a string is a famous example of spontaneous animal problem solving. The “insight” hypothesis claims that this complex behaviour is based on cognitive abilities such as mental scenario building and imagination. An operant conditioning account, in contrast, would claim that this spontaneity is due to each action in string pulling being reinforced by the meat moving closer and remaining closer to the bird on the perch. We presented experienced and naïve New Caledonian crows with a novel, visually restricted string-pulling problem that reduced the quality of visual feedback during string pulling. Experienced crows solved this problem with reduced efficiency and increased errors compared to their performance in standard string pulling. Naïve crows either failed or solved the problem by trial and error learning. However, when visual feedback was available via a mirror mounted next to the apparatus, two naïve crows were able to perform at the same level as the experienced group. Our results raise the possibility that spontaneous string pulling in New Caledonian crows may not be based on insight but on operant conditioning mediated by a perceptual-motor feedback cycle.