Grey parrot (Psittacus erithacus) abilities for visual inferential reasoning by exclusion were tested in two experiments. The first replicated the Grey parrot study of Mikolasch, Kotrschal, and Schloegl (2011, African Grey Parrots (Psittacus erithacus) use inference by exclusion to find hidden food. Biology Letters, 7, 875-877), which in turn replicated that of Premack and Premck (1994, Levels of causal understanding in chimpanzees and children. Cognition, 50, 347-362) with apes, to learn if our subjects could succeed on this task. Here parrots watched an experimenter hide two equally desirable foods under two separate opaque cups, surreptitiously remove and then, in view of the birds, pocket/eat one of the foods, leaving birds to find the still baited cup. The experiment contained controls for various alternative explanations for the birds' behavior, but birds might still have avoided a cup from which something had been removed rather than specifically tracking the eaten food. Thus, in the second experiment, some trials were run with one food slightly more preferred than the other, during which two items of each type were hidden and only one of the items were removed from one cup. Sessions also included Experiment 1-type trials to see if birds tracked when and when not to use exclusion. Thus, birds would be rewarded for attending closely to all the experimental aspects needed to infer how to receive their preferred treat. Three of four birds succeeded fully.

Linking specific cognitive abilities of nonhuman species on a laboratory task to their evolutionary history-ecological niche can be a fruitful exercise in comparative psychology. Crucial issues, however, are the choice of task, the specific conditions of the task, and possibly the subjects' understanding or interpretation of the task. Salwiczek et al. (2012) compared cleaner wrasse fish (Labroides dimidaitus) to several nonhuman primate species (capuchins, Sapajus paella; chimpanzees, Pan troglodytes; orangutans, Pongo abelii) on a task purportedly related to the ecological demands of the fish, but not necessarily of the nonhuman primates; fish succeeded whereas almost all of the nonhuman primates that were tested failed. We replicated the two-choice paradigm of the task with three Grey parrots (Psittacus erithacus), whose ecology, evolutionary history, and cortical capacity are arguably more like those of nonhuman primates than fish. Greys succeeded at levels more like fish than all the nonhuman primates, suggesting possible alternative explanations for their success. Fish and nonhuman primate subjects also experienced a reversal of the initial conditions to test for generalization: Greys were similarly tested; they performed more like fish and capuchins (who now succeeded) than the apes (who continued to fail).

Contrafreeloading is the choice to perform a physical task to access food over freely available food, a behavior pattern contrary to the predictions of both optimal foraging and learning theories. This study examined the presence and degree of contrafreeloading in Grey parrots (Psittacus erithacus) and the possible interpretation of such behavior in the context of play. Experiment 1 presented 4 subjects, Griffin, Athena, Franco and Pepper, with container pairs holding more-or less-preferred free or enclosed food items. Degrees of contrafreeloading were classified as follows: calculated contrafreeloading (working to access preferred food over less-preferred, freely available food); classic contrafreeloading (working to access food equal in value to freely available food); and super contrafreeloading (working to access a less-preferred food over preferred, freely available food). Of these three, Griffin significantly preferred classic and calculated contrafreeloading; Athena, Pepper, and Franco significantly preferred calculated contrafreeloading. Experiment 2 examined a more ecologically relevant contrafreeloading task in 5 parrots, Griffin, Athena, Lucci, Pepper, and Franco, using shelled and unshelled nuts. Athena and Franco significantly preferred cracking the shell to obtain the nut (contrafreeloading); Griffin and Lucci did not; Pepper chose at chance. We examine numerous possible explanations for their behavior and suggest that individual differences in contrafreeloading among the Grey parrots could relate to which task each considers some form of play.

An understanding of Piagetian liquid conservation was investigated in four Grey parrots (), their ages ranging from initially less than 1 year old to 18 years old. They were tested in several conditions: on the ability to choose between (a) identical containers filled with a greater or lesser quantity of a desirable liquid to see if they would reliably take the larger amount and (b) equal quantities of liquid that were visibly or invisibly transferred from identical to different-sized containers to examine their abilities with respect to conservation. Invisible transfers examined the extent to which birds chose based on perceptual evaluations of quantity and the effects of task order on their decisions. Adult birds succeeded on all or most aspects of the tests. As a chick (∼6 months), 1 bird was unable or unwilling to choose between the smaller and larger quantities in the first stage of testing, but upon reaching juvenile status succeeded in all aspects of the tests. Grey parrots thus demonstrate some understanding of liquid conservation. (PsycINFO Database Record

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