A Grey parrot (Psittacus erithacus), able to quantify sets of eight or fewer items (including heterogeneous subsets), to sum two sequentially presented sets of 0–6 items (up to 6), and to identify and serially order Arabic numerals (1–8), all by using English labels (Pepperberg in J Comp Psychol 108:36–44, 1994; J Comp Psychol 120:1–11, 2006a; J Comp Psychol 120:205–216, 2006b; Pepperberg and Carey submitted), was tested on addition of two Arabic numerals or three sequentially presented collections (e.g., of variously sized jelly beans or nuts). He was, without explicit training and in the absence of the previously viewed addends, asked, “How many total?” and required to answer with a vocal English number label. In a few trials on the Arabic numeral addition, he was also shown variously colored Arabic numerals while the addends were hidden and asked “What color number (is the) total?” Although his death precluded testing on all possible arrays, his accuracy was statistically significant and suggested addition abilities comparable with those of nonhuman primates.
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With respect to noncompliance: In earlier studies (e.g., Pepperberg 1992; Pepperberg and Gordon 2005; Pepperberg and Lynn 2000), Alex, caring little for any reward, realized he could quickly finish a test no matter what he said. After learning his trainers would persevere, he realized he had to respond correctly for a test to end.
Wooden numerals—the initial stimuli when he was taught Arabic numerals–were always standardized with nontoxic paints for which Alex learned to use a specific color label; however, he chewed these numerals as his reward and they could not be replaced. We thus had to use magnetized plastic “refrigerator letters” for much of this study, and color errors occurred with these numerals. Paint that sticks to plastic is toxic, and because Alex is given the numeral to chew as his initial reward, could not be used. Note he did not always err on such items and would answer correctly when asked a second time, suggesting that the color clearly was on a boundary (e.g., if not yellow or red, it had to be orange).
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This study was supported by many donors to The Alex Foundation. I thank Harrison’s Bird Diet and Fowl Play for food and treats, Avian Adventures for Alex’s cage, Carol D’Arezzo for Alex’s perch, and the several students who assisted in testing. This manuscript was written under the support of donors to The Alex Foundation (particularly Anita Keefe, the Michael Haas Foundation, and the Sterner family) and NSF grant BCS-0920878 (to Ken Nakayama). The study procedures comply with the current laws of the country under which they were performed.
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Pepperberg, I.M. Further evidence for addition and numerical competence by a Grey parrot (Psittacus erithacus). Anim Cogn 15, 711–717 (2012). https://doi.org/10.1007/s10071-012-0470-5
- Parrot cognition
- Parrot numerical competence
- Nonhuman addition
- Avian cognition