Zero is supposed to be an abstract concept. It was the last numeral to be created in most numerical systems, as it is not a counting number. The ancient peoples of the Indus Valley Civilization used fractions and negative numbers, but were unsure of the concept zero. Greeks had long philosophical discussions about the concept of zero! The first documented mention of zero is near 300 AD by Indian mathematicians.

Alex the Parrot (Courtesy: GEAE)Now it seems a bird has grasped the zero, even though it took us humans such a long time to get our arms around it:). Alex, a 28-year-old African gray parrot who lives in a lab at Brandeis University in Massachusetts, has a brain the size of a walnut. But when confronted with no items on a tray where usually there are some, he says 'none':):).
Today, zero might not seem to be such an abstract concept to us. But kids are unable to grasp the concept till they are about the age of three to four! The result, published in the current issue of the Journal of Comparative Psychology, adds to growing evidence that birds and other animals are smarter than we thought:):). Perhaps we should look at the word 'bird-brain' with some respect from now on:D.