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 non-intuitive 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.