Other Animals
African grey parrot, African grey, grey
Griffin preens to distract himself during a trial. Image courtesy of Dr. Irene Pepperberg

Simply stated, “executive function” means using the rational bit of your brain rather than the emotional bit to make a decision. Executive function generally involves three main aspects of behavior (Diamond, 2013)—inhibitory control (thinking about the results of one’s actions and resisting impulsive behavior), working memory (keeping track of the various possible outcomes of one’s actions), and cognitive flexibility (being able to switch between tasks so as to do what is needed when it is needed). Executive function thus refers to a suite of skills that, when used together, correlate with successful behavior in various aspects of life, as it allows an individual to choose the most beneficial plan of action. It is the inhibitory control aspect, however, that is the best-known, because of the famous “Marshmallow Test” performed by Mischel (1974).

Delayed Gratification Test

The Test was quite simple: Mischel studied a large number of 4-year-old children. He sat each child down in a room in front of a table that had a marshmallow on a plate. He told the child that he had to run an errand, and if the child could sit there and NOT eat the marshmallow until he returned, he would bring back a second marshmallow for the child to eat. He told the child that they could eat what was on the plate at any time, but if they did so, they forfeited the second marshmallow. He made them wait 15 minutes—an eternity to a 4-year-old! Nevertheless, a percentage of the children did wait. Those who did, usually distracted themselves in some way—by singing, dancing around, napping, etc. The most interesting part, however, was that when Mischel tracked these children many years later, he found that those who had waited had had greater success in every part of their lives (schooling, careers, relationships, etc.; Shoda et al., 1990).

For those of us who study animal behavior, the idea of a cross-species comparison was intriguing, especially for those of us who work with parrots! We tend to think of the social skills of parrots as equivalent to those of 2-year-old children…creatures who want what they want immediately, with little capacity to wait. But what if that wasn’t exactly true?

Can Parrots Show Patience?

As it turns out, parrots are pretty good at waiting for better rewards. Studies in cockatoos (Auersperg et al., 2013) and African grey parrots (Koepke et al., 2015) showed they will wait for a considerable amount of time for a superior treat—but not for more of a treat, even a really desirable one, and I’ve written about this before. Griffin, for example, would wait 15 mins for a better treat (and, like the children, distracted himself while waiting; see Figure and earlier blog) but not even a minute for more (Koepke et al., 2015; Pepperberg & Rosenberger, 2022). Ecologically, it makes sense: Avian foragers might fly over an acceptable food source en route to one of better quality to gain more calories per expended effort; however, stopping for a small quantity en route to a larger, equal quality source likely poses few risks, particularly if the larger source could attract more competition.

A Waiting Game Is Hatched

But what might help birds to learn to wait for more? If we found some procedure that worked for our parrots, might the birds then be a model for human children? Most importantly, however, we didn’t simply want to train the birds to wait, as one might train a dog. For dogs, “stay” is a command and they generally respond by simply remaining in place (as they are trained to do—by reinforcement and possible punishment) until they receive a specific release. Although one might argue that they have a choice to obey, they cannot disobey without serious consequences (e.g., no reward at all or possible punishment). The dog’s behavior thus really has nothing to do with choice—which is the entire point of executive function—a voluntary decision to do something that has positive future consequences. After reading a lot of literature on children and even apes, we came up with a plan…

We used something called “symbolic representation.” Now, Griffin already knew that different vocalizations symbolized different objects, attributes, and actions; we then trained Griffin to correlated symbols—little wooden hearts—with pieces of cashews. Thus, each heart represented a chunk of cashew, and if he chose the larger number of hearts compared to a smaller number, he got to eat the bigger number (Pepperberg & Rosenberger, 2022). The next step was to see if he would wait for more hearts; that is, he no longer had to sit in front of a yummy nut for some period of time in order to get several yummy nuts; now he just had to sit and wait for more hearts—which would result in getting him more nuts. But the “siren call” of the nut was no longer tempting him from moment to moment.

He succeeded very well (Pepperberg & Rosenberger, 2022), waiting for up to 15 minutes, and on almost all his trials. And he wasn’t simply trained to wait. When we showed him the larger number of hearts and asked him to wait for the smaller number (a control for training—if he were trained, he’d wait whatever the number), he looked at us as though we were crazy and immediately tapped the container holding the hearts. But would that transfer to actual nuts?

We thus tested him and also tested two other African grey parrots who are companion animals, Pepper and Franco, who have succeeded in several other experiments in our lab (e.g., Pepperberg & Hartsfield, 2014), but who hadn’t been part of the heart study. They do, however, live in a household where they are treated more like family members than pets—which means they often have to wait their turn to take part in various activities, so that they, like Griffin, understand the meaning of “wait”.

Showing Patience For Nuts

Griffin now was able to wait, again for 15 minutes, for more nuts; he also appropriately failed control trials, where we gave him more nuts and asked him to wait for a smaller amount. What was really interesting, however, were the results from Pepper and Franco! (Pepperberg & Hartsfield, 2023).

Neither Pepper nor Franco cared for the task—they really disliked being ignored by their human caretaker during the waiting period. We actually ended the study early for them so as not to stress them. But even with far fewer trials, we learned quite a bit. First, Pepper, who was initially succeeding in all her trials—including one for 15 mins!—realized that if she chose not to wait, she could reconnect with her human…something she wanted more than treats, so she stopped waiting! And Franco, who didn’t wait nearly as long as either Griffin or Pepper, still waited for up to 5 minutes. Remember, that without the experience with hearts, Griffin would barely wait a minute.

So, we learned several things. First, that experience with the hearts helped strengthen Griffin’s executive function; maybe such experience would help children who initially fail the Marshmallow Test. Second, Pepper was smart enough to figure out how to get what she really wanted; we know that some children also wouldn’t wait for reasons that made sense to them (e.g., they didn’t believe or trust that the researcher would return with the second treat). Third, even Franco, who was struggling somewhat with the task, could wait a decent amount of time. Fourth, although Pepper and Franco didn’t have Griffin’s experience, they DID have lots of practical experience in their home life with turn-taking and waiting—and one study has shown that children who have such experience can pass the Marshmallow Test even before they are four years old—a striking finding (Russell et al., 2013). So, the take-home lesson: Experiences of all sorts seem to have a significant effect on subjects’ behavior!



Auersperg, A. M. I., Laumer, I. B., & Bugnyar, T. (2013). Goffin cockatoos wait for qualitative and quantitative gains but prefer ‘better’ to ‘more’. The Royal Society: Biology Letters, 9, Article 20121092

Diamond, A. (2013). Executive functions. Annual Review of Psychology, 64(1), 135–168.

Koepke, A., 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, 339-346.

Mischel, W. (1974). Processes in delay of gratification. In L. Berkowitz (Ed.), Advances in experimental social psychology, Vol. 7 (pp. 249–292). New York, NY: Academic Press.

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, 298–306.

Pepperberg, I. M., & Hartsfield, L. A. (2023). A study of executive function in Grey parrots (Psittacus erithacus): Experience can affect delay of gratification. Journal of Comparative Psychology. Advance online publication.

Pepperberg, I. M., & Rosenberger, V. A. (2022). Delayed gratification: A Grey parrot (Psittacus erithacus) will wait for more tokens. Journal of Comparative Psychology, 136(1), 79–89.

Russell, B. S., Londhe, R., & Britner, P. A. (2013). Parental contributions to the delay of gratification in preschool-aged children. Journal of Child and Family Studies, 22(4), 471–478.

Shoda, Y., Mischel,W., & Peake, P. K. (1990). Predicting adolescent cognitive and self-regulatory competencies from preschool delay of gratification: Identifying diagnostic conditions. Developmental Psychology, 26, 978–986.

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