The authors evaluated the ontogenetic performance of a grey parrot (Psittacus erithacus) on object permanence tasks designed for human infants. Testing began when the bird was 8 weeks old, prior to fledging and weaning. Because adult grey parrots understand complex invisible displacements (I. M. Pepperberg & F. A. Kozak, 1986), the authors continued weekly testing until the current subject completed all of I. C. Uzgiris and J. Hunt's (1975) Scale 1 tasks. Stage 6 object permanence with respect to these tasks emerged at 22 weeks, after the bird had fledged but before it was completely weaned. Although the parrot progressed more rapidly overall than other species that have been tested ontogenetically, the subject similarly exhibited a behavioral plateau part way through the study. Additional tests, administered at 8 and 12 months as well as to an adult grey parrot, demonstrated, respectively, that these birds have some representation of a hidden object and understand advanced invisible displacements.
Pepperberg, I. M., Willner, M. R., & Gravitz, L. B. (1997). Development of Piagetian object permanence in grey parrot (Psittacus erithacus). Journal of Comparative Psychology, 111(1), 63.