Ontogeny of object permanence and object tracking in the carrion crow, Corvus corone

Object permanence is a component of physical cognition and refers to the knowledge that an object still exists when out of sight or displaced. Many animal species develop object permanence skills in a similar sequence as human infants, but few master the most complex aspects, such as representing invisibly displaced objects. We tested six developing, hand-raised carrion crows on Piagetian object permanence applying a randomized presentation of Uzgiris & Hunt’s (1975, Assessment in Infancy: Ordinal Scales of Psychological Development, University of Illinois Press) Scale 1 tasks. In addition, the birds were tested on transpositions, visible and invisible rotational displacement tasks. The results from this longitudinal study demonstrate that young carrion crows did develop full Piagetian object permanence skills including Stage 6 (with the exception of task 15). This ability developed gradually, albeit with slight changes in the order of mastery compared to human infants. Systematically different points in time at which same-aged crows mastered the tasks indicated interindividual cognitive differences. The crows showed perseverative searches at a previously rewarded location (the so-called ‘A-not-B error’). They mastered visible rotational displacements consistently, but failed at more complex invisible rotational displacements. The overall pattern of the development and competence of object permanence in crows is similar to other corvid species. The absolute ages at which corvid species pass the tests seem to be a function of the hatching-to-fledging time. The findings may reflect maturing executive functions rather than being related to food-storing habits.