A new study suggests that some birds may have a better grasp of numbers than the average three-year-old child.
Researchers have shown that an African gray parrot may comprehend the mathematical concept of zero—an abstract notion that human children rarely understand until around four years of age.
The concept of zero is surprisingly difficult to grasp, even for people.
"There is some understanding of nonexistence that seems to develop naturally, but the actual use of the term 'zero' seems to need to be taught," said comparative psychologist Irene Pepperberg. Pepperberg conducted the study at Brandeis University in Waltham, Massachusetts.
The idea of zero as a nonexistent quantity was not obvious to early human cultures, Pepperberg said. Most Europeans lacked a term for it until the 1600s.
Researchers in the United States and Japan have previously shown that chimpanzees and possibly squirrel monkeys can comprehend zero when taught. Chimps have also used it when adding and subtracting quantities of objects. Now a precocious 28-year-old parrot named Alex may have provided the first evidence of animals other than primates getting it too.
For 27 years Pepperberg has tutored Alex to understand the English names of 50 different objects—such as "banana," "truck," and "grape"—plus the names of seven colors, five shapes, and the numbers one through six.
Pepperberg's most recent research with Alex, co-authored with Brandeis graduate student Jesse D. Gordon, is detailed in the current issue of the Journal of Comparative Psychology.
It not only shows that Alex can count jelly beans, colored blocks, and other objects but also hints that he may have spontaneously come up with a "zero-like concept."
During one experiment Alex was presented with blocks in differently colored sets of two, three, and six. When researchers asked Alex which color group had five blocks, he answered, "None." This prompted Pepperberg to set up a series of tests in which the parrot consistently identified zero quantities of objects with the label "none."
Alex had been taught the term "none" to indicate when neither of two identically sized objects was larger than the other. He had also used it to indicate when there was no difference in other qualities, such as color or shape, among a set of objects.
But Alex had never been taught to use "none" to indicate an absence of a quantity—that idea he apparently came up with by himself.
"That Alex transferred the notion from other domains to quantity, without training or prompting by humans, was unexpected," Pepperberg said.
She believes that, after several weeks in which Alex had seemed disinterested in the experiments, the development was possibly an "attempt to make the procedure more challenging."
The findings indicate that Alex may understand the concept of zero, but far more rigorous testing would be required to prove it, Sally Boysen said. Boysen is an animal-cognition expert at Ohio State University's Chimpanzee Center in Columbus, Ohio.
Boysen's work in 1989 showed that chimpanzees could understand the idea of zero and use it when adding quantities of objects.
Boysen argued that Alex's use of "none" could just be a default response, which he uses when he's unable to identify the number of objects in front of him. He may not understand how to add or subtract zero as a quantity, she added.
Pepperberg agreed that more work is required to prove that African gray parrots can be taught to understand abstract numerical notions in the same way as people.
"[Alex's 'none'] isn't the same concept of zero that you and I have," Pepperberg said. "That's why I call it a 'zero-like' concept. We are working to refine our knowledge of what this concept actually is."
In the wild, African gray parrots would require at least a basic understanding of more-versus-less when foraging in their jungle habitat, Pepperberg said. Counting might also be useful when deciphering vocalizations or tracking the number of parrots in a flock.
"That zero was represented in some way by a parrot, with a walnut-sized brain … is striking," Pepperberg said. "Evolutionarily the connection [of birds] to humans is ancient … yet their brains seem to have homologues [structural similarities] to ours."