boobook owl, both predators of the magpie's young. Auditory map Some birds, such as the Australian magpie, mimic only those noises it hears whilst in its territory. It has been suggested that birds with complex social organisation may develop an auditory map of their territory, as well as visual, and that mimicking facilitates this process. Cognition controversy There is controversy about whether parrots are capable of using language, or merely mimic what they hear. However, some scientific studies—for example those conducted over a 30-year period by Irene Pepperberg with a grey parrot named Alex and other parrots, covered in stories on network television on numerous occasions—have suggested that these parrots are capable of using words meaningfully in linguistic tasks. Some in the scientific community are skeptical of Pepperberg's findings, pointing to Alex's communications as operant conditioning. Critics point to the case of Clever Hans, a horse whose owner claimed could count, but who instead was actually understanding subtle cues from him. In another case, Nim Chimpsky, a chimpanzee, was thought to be using language, but there is some debate over whether he simply imitated his teacher. Dr. Herbert Terrace, who worked with Nim Chimpsky, says he thinks Alex performed by rote rather than using language; he calls Alex's responses "a complex discriminating performance", adding that in every situation, "there is an external stimulus that guides his response." However, supporters of Alex mention that Alex was able to talk to and perform for anyone involved in the project as well as complete strangers who recorded findings unassisted and during first contact with the bird, making the arguments of rote learning and operant conditioning difficult to substantiate. Scientists in France and the Czech Republic have also had some success in teaching grey parrots to label items referentially using human language, albeit using a different teaching methodology to that of Pepperberg—which was found to be ineffective in the case of the particular birds within the study. Famous talking birds Alex, a grey parrot, had a vocabulary of about 100 words, substantially fewer than world record holders, but he is perhaps the best known talking bird due to the publicity surrounding his potential cognitive abilities. In learning to speak, Alex showed scientist Irene Pepperberg that he understood categorization like "same and different" and "bigger and smaller". He could identify objects by their shape ("Three-corner", "Four-corner", up to "Six-corner") and material: when shown a pom-pom