Testing Problem Solving in Ravens: String-Pulling to Reach Food

The aim of our study was to re-examine the acquisition of problem-solving behaviour in ravens: accessing meat suspended from a perch by a string. In contrast to a previous study, here we: (i) controlled for possible effects of fear of the string, competition by dominants, and social learning and (ii) devised a mechanically equivalent but non-intuitive task to test for the possibility of means– end understanding. One-year-old ravens confronted with meat on a string for the first time tried several ways to reach the food. However, five of six birds suddenly performed a coherent sequence of pulling up and stepping on loops of string, essential for solving the problem. Those five birds were also successful in the nonintuitive task where they had to pull down the string to lift the meat. A second group of birds with similar exposure to strings but without any experience in pulling up meat failed the pull-down test. These results support the idea that the ravens behaviour in accessing meat on a string is not only a product of rapid learning but may involve some understanding of cause–effect relation between string, food and certain body parts.