An African Grey Parrot at Brandeis University appears to understand a numerical concept akin to zero. In a series of counting experiments, Alex, a 28-year-old parrot who lives in a Brandeis lab run by comparative psychologist Irene Pepperberg, spontaneously and correctly used the label "none" during trials of his counting skills to describe an absence of colored blocks on a tray.
The findings, published in the current issue of The Journal of Comparative Psychology, add to a growing body of scientific evidence that the avian brain, though quite different from the brains of mammals, are capable of handling more complex processes than previously thought.
Generally, humans don't begin to understand the concept of zero until about three or four years old (longer in the case of some). Chimps and spider monkeys have been shown to have some rudimentary understanding of the concept of none. Grey parrots have brains the size of a walnut.