Parrots can say words, but most of them are only copying sounds. Alex, an African gray parrot, was different. A scientist named Pepperberg worked with him for almost 30 years.

Alex could name colors and count up to six. When the answer was "nothing," he said "none." This was like the idea of zero. He seemed to understand the meaning of some words.

Most talking parrots simply imitate sounds without understanding them. An African gray parrot named Alex suggested that some parrots may understand more. For almost 30 years, the researcher Pepperberg trained him with a special method.

Alex watched two people ask and answer questions, and he learned by seeing the correct person get praised. In a 2005 study, Alex was shown mixed groups of colored objects and asked questions like "Which color has four?" He answered correctly more than 80 percent of the time.

When no group matched the number, he said "none." That is close to the idea of zero. Scientists have also found that parrot brains have a special song system.

Most talking parrots are vocal mimics, reproducing sounds without linking them to meaning. Alex, an African gray parrot that Pepperberg trained from the 1970s until his death in 2007, seemed to be an exception. His training tied words directly to things. In a model/rival technique, two humans acted out questions and answers, and the one who answered correctly was praised. When Alex named an object, he got that very object as a reward.

In a 2005 study with Gordon, Alex looked at mixed sets of objects and answered questions such as which color had four items. He had never been trained on that format, yet he was right more than 80 percent of the time, whatever the objects' size or shape. When no set matched, he said "none," which the researchers called a zero-like concept.

All of this comes from a single bird, though, and his abilities may not generalize to other parrots. Trainers can also give unintentional cues, the so-called Clever Hans effect, which the researchers had to guard against. A possible basis turned up in 2015, when Chakraborty and colleagues found that parrots have a "shell" song system wrapped around the core system shared with other vocal-learning birds.