Research and Links

Dr. Irene Pepperberg has been studying the intelligence and reasoning abilities of the African Grey parrot for almost 40 years. She has published consistently and extensively in some of the most highly respected scientific journals in her field.

Below is a partial list of her papers with links to download in PDF format. If you don’t have Adobe Acrobat Reader, which is necessary to view PDF files, you can download it free by clicking here.

These papers are being provided for private use only, and cannot be published or reprinted without the express permission of the publisher. Quotes from these articles can be used only within the specifications of each publisher. Please consult the individual publishers about their particular guidelines.

We hope you’ll enjoy reading some of Dr. Pepperberg’s research, which has demonstrated the amazing intelligence of African Grey parrots to the scientific world. The list of papers available for download will be expanded as time permits.



Bharatharaj, J., Pepperberg, I.M., Kutty, S.K.S., Munisamy, A. & Krägeloh, C. (2023). Exploring the utility of robots as distractors during a delay-of-gratification task in preschool children. Frontiers in Robotics and AI, Vol 10,  doi: 10.3389/frobt.2023.1001119

Smith, G.E., Bastos, A.P.M., Taylor, A.H., & Pepperberg, I.M., (2022). Contrafreeloading in kea (Nestor notabilis) in comparison to Grey parrots (Psittacus erithacus). Sci. Rpts. 12:17415 doi:10.1038/s41598-022-21370-6.

Pepperberg, I.M. (2021b). Does captivity alter problem-solving behavior in Goffin’s cockatoos? Learn. Behav. Doi: 10.3758/s13420-020-00458-x

Pepperberg, I.M. (2021a). How do a pink plastic flamingo and a pink plastic elephant differ? Evidence for abstract representations of the relations same-different in a Grey parrot. Current Opinion in Behavioral Sciences, 37, 146-152.

Pailian, H., Carey, S., Halberta, J, Feigenson, L., & Pepperberg, I.M. (2020). Age and species comparisons of visual mental manipulation ability as evidence for its development and evolution. Special issue of Scientific Reports, 10, Article number: 7689, doi:10.1038/s41598-020-64666-1

Cornero, F.M., Harstfield, LA., & Pepperberg, I.M. (2020). Piagetian liquid overconservation in Grey parrots (Psittacus erithacus). J. Comp. Psychol., 143:197-210. doi:10.1037/com0000209

Pepperberg, I.M. (2020a). The comparative psychology of intelligence: Some thirty years later. In special issue of Frontiers in Psychology: Comparative Psychology, D. Scarf, ed, 11:973. doi: 10.3389/fpsyg. 2020.00973

Pepperberg, I.M. (2020b) Vocal communication in nonhuman animals: View from the wings. In special issue of Animal Behavior and Cognition, “Communication in Nonhumans: The Forty Year Anniversary of Seyfarth, Cheney and Marler”, 7(2), 95-100. doi: 10.26451/abc.

Pepperberg, I.M. (2020c) Human-avian comparisons in cognitive performance. Cambridge Handbook of Evolutionary Perspectives on Human Behavior, L. Workman, W. Reader, & J. Barkow, eds., Cambridge, UK: Cambridge University Press, pp. 3-13.

Pepperberg, I.M., Gray, S.L., Cornero, F.M., Mody, S., & Carey, S. (2019). Logical reasoning by a Grey parrot (Psittacus erithacus)? A case study of the disjunctive syllogism. Behaviour 156:409-445.

Pepperberg, I.M. (2019a). Animal sentience is not enough to motivate conservation. Commentary on Chapman, C.A., & Huffman, M.A. (2018). Why do we want to think humans are different? Animal Sentience 21(3).

Pepperberg, I.M. (2019b). Grey parrots: Studies in avian cognition. Encyclopedia of Animal Behavior, 2nd ed. J. Choe, ed., Oxford, pp. 83-89.

Clements, K., Gray, S.L., Gross, B., & Pepperberg, I.M. (2018). Initial evidence for probabilistic learning by a Grey parrot (Psittacus erithacus). J. Comp. Psychol. 132:166-177. doi: 10.1037/ com0000106

Pepperberg, I.M. (2018a). Grey parrots: Cognitive and communicative abilities. A Practical Guide to Animal Cognition, N. Bueno & F. Amici, eds, Cambridge, UK: Cambridge University Press

Pepperberg, I.M. (2018b/2019). Tool use in Goffin’s cockatoos: shape/frame matching. Learning & Behavior, 47:1-2.

Pepperberg, I.M. (2018c). Zero concept. Encyclopedia of Animal Behavior and Cognition, J. Vonk & T. Schackelford (Eds.). Springer.

Pepperberg, I.M. (2018d). Cardinality. Encyclopedia of Animal Behavior and Cognition, J. Vonk & T. Schackelford (Eds.). Springer.

Pepperberg, I.M., Gray, S., Lesser, J.S., & Hartsfield, L.A. (2017). Piagetian liquid conservation in Grey parrots (Psittacus erithacus). J. Comp. Psychol. 131:370-383. 10.1037/com0000085

Pepperberg, I.M. (2017a). Alex the Parrot. In J. Vonk & T.K. Shackelford (Eds.), Encyclopedia of Animal Cognition and Behavior, Springer

Pepperberg, I.M. (2017b). “Birdbrains” should not be ignored in studying the evolution of G. Commentary, Behav. Brain Sci, 40: e216. DOI: /10.1017/S0140525X16001758

Pepperberg, I.M. (2017c) Review of studies on visual perception in Grey parrots (Psittacus erithacus: The Müller-Lyer illusion, modal and amodal completion. Animal Behavior & Cognition, 4(3):378-395.Special issue on “Comparative Perception”. doi:10.12966/abc.08.0X.2017

Pepperberg, I.M. (2017d) Avian numerical cognition. In Avian Cognition, S. Healy & C. ten Cate (Eds.), Cambridge University Press.

Call, J., Burghardt, G.M., Pepperberg, I.M., Snowdon, C.T., & Zentall, T.R. (2017). What is comparative psychology? In APA Handbook of Comparative Psychology, J. Call, I.M. Pepperberg, C.T. Snowdon, T.R. Zentall (Eds), American Psychological Association Press

Pepperberg, I.M. (2017e). Symbolic communication in nonhumans. In APA Handbook of Comparative Psychology, J. Call, I.M. Pepperberg, C.T. Snowdon, T.R. Zentall (Eds), American Psychological Association Press

Pepperberg, I.M. (2017f). Interspecific communication. In APA Handbook of Comparative Psychology, J. Call, I.M. Pepperberg, C.T. Snowdon, T.R. Zentall (Eds), American Psychological Association Press

Griebel, U., Pepperberg, I.M., Oller, D.K. (2016) Developmental plasticity and language: A comparative perspective. Topics in Cognitive Science 8:435-445.

Pepperberg, I. M. (2016). Animal language studies: What happened? Psychonomic Bulletin & Review Psychon Bull Rev. doi:10.3758/s13423-016-1101-y

Pepperberg, I. M., & Nakayama, K. (2016). Robust representation of shape in a Grey parrot (Psittacus erithacus). Cognition, 153, 146-160. doi:10.1016/j.cognition.2016.04.014

Koepke, A. E., Gray, S. L., & Pepperberg, I. M. (2015). Delayed gratification: A grey parrot (Psittacus erithacus) will wait for a better reward. Journal of Comparative Psychology, 129(4), 339-346. doi:10.1037/a0039553

Pepperberg, I. M. (2015). Reply to Jaakkola (2014): “Do animals understand invisible displacement? A critical review”. Journal of Comparative Psychology, 129(2), 198-201. doi:10.1037/a0038319

Pepperberg, I. M., & Hartsfield, L. A. (2014). Can Grey parrots (Psittacus erithacus) succeed on a “complex” foraging task failed by nonhuman primates (Pan troglodytes, Pongo abelii, Sapajus apella) but solved by wrasse fish (Labroides dimidiatus)? Journal of Comparative Psychology, 128(3), 298-306. doi:10.1037/a0036205

Péron, F., Thornberg, L., Gross, B., Gray, S., & Pepperberg, I. M. (2014). Human–Grey parrot (Psittacus erithacus) reciprocity: A follow-up study. Animal Cognition Anim Cogn, 17(4), 937-944. doi:10.1007/s10071-014-0726-3

Pepperberg, I. M., Koepke, A., Livingston, P., & Hartsfield, L. A. (2013). Reasoning by inference: Further studies on exclusion in grey parrots (Psittacus erithacus). PsycEXTRA Dataset. doi:10.1037/e598032013-086

Pepperberg, I. M. (2012). Further evidence for addition and numerical competence by a Grey parrot (Psittacus erithacus). Animal Cognition Anim Cogn, 15(4), 711-717. doi:10.1007/s10071-012-0470-5

Pepperberg, I.M., Carey, S. (2012). Grey Parrot Number Acquisition: The Inference of Cardinal Value from Ordinal Position on the Numeral List COGNIT2474

Péron, F., John, M., Sapowicz, S., Bovet, D., & Pepperberg, I. M. (2012). A study of sharing and reciprocity in grey parrots (Psittacus erithacus). Animal Cognition Anim Cogn, 16(2), 197-210. doi:10.1007/s10071-012-0564-0

Schachner, A., Brady, T. F., Pepperberg, I. M., & Hauser, M. D. (2009). Spontaneous Motor Entrainment to Music in Multiple Vocal Mimicking Species. Current Biology, 19(10), 831-836. doi:10.1016/j.cub.2009.03.061

Pepperberg, I.M., Vicinay, J., Cavanagh, P. (2008) The Muller-Lyer illusion is processed by a Grey Parrot (Psittacus erithacus). Perception 37:765-781.

Pepperberg, I.M. (2007a). Grey parrots do not always “parrot”: Phonological awareness and the creation of new labels from existing vocalizations. Language Sciences 29: 1-13.

Pepperberg, I.M. (2006a). Ordinality and inferential abilities of a Grey Parrot (Psittacus erithacus)Journal of Comparative Psychology, 120: 205-216.

Pepperberg, I.M. (2006b). Grey Parrot (Psittacus erithacus) numerical abilities: addition and further experiments on a  zero-like concept. Journal of Comparative Psychology, 120: 1-11.

Pepperberg, I.M., and Gordon, J.D. (2005). Number Comprehension by a Grey Parrot (Psittacus erithacus), Including a Zero-Like ConceptJournal of Comparative. Psychology, 2005, Vol. 119, No. 2, 197-209

Pepperberg, I.M. (2001). Lessons from cognitive ethology: Animal models for ethological computing. Proceedings of the First Conference on Epigenetic Robotics, C. Balkenius, J. Zlatev, H. Kozima, K. Dautenhahn, & C. Breazeal, Eds., Lund University Cognitive Science Series No. 85, Lund, Sweden (online only)

Pepperberg, I.M., Willner, M.R., and Gravitz, L.B. (1997). Development of Piagetian object permanence in a Grey parrot (Psittacus erithacus). J. Comp. Psych. 111:63-75.


Links announcing the Pepperberg birds’ achievements

and other related news.

We appreciate and are pleased by this excellent review of our research on Grey parrot cognition and communication. We do, however, wish to clarify two points. First, signing chimpanzees did question their human companions—although these questions were, according to the Fouts’ (1993), used more as clarifications than as actual requests for information. Second, we ourselves might not consider Alex’s question about the color he viewed in a mirror as ‘existential’—the most parsimonious interpretation could have been simple interest in what he was viewing.
-Irene M. Pepperberg, PhD
Fouts, R.S., & Fouts, D.H. (1993). Chimpanzees’ Use of Sign Language. In P. Cavalieri & P. Singer (eds.), The Great Ape Project. New York: St. Martin’s Griffin, pp. 28-41.

Did you find a link not here? Please send it to us from our contact page