Asked to put animals in order of intelligence, most people would put birds somewhere near the bottom. They are much smaller than us, they have small brains, and they look completely different. But there is more than one way to be intelligent.

In humans and other apes the cerebral cortex is large. In birds, another part of the brain - the hyperstriatum - is large instead. More intelligent mammals (such as chimpanzees) have proportionately bigger cortices than less intelligent ones (such as hamsters); in the same way, smart birds, such as parrots and crows, have especially big hyperstriata.

Because most scientists don't think birds are smart, they treat them as if they were stupid.

They put a pigeon in a box and test his or her reactions as if these were the result of nothing more than a set of "responses" which were ultimately linked to some kind of reward. Those scientists who have thought outside the box on this one have had some surprises.

At the University of Arizona Irene Pepperberg has spent the last twenty five years teaching parrots to understand and talk about abstract concepts such as colour, size and material. Her star pupil is called Alex.

If Alex is shown a blue object and a red object, and is asked "how different?" he will identify that they are different in colour. This also works with objects that he has never seen before. If he is shown two objects which differ in both size and colour, he can correctly identify "what colour bigger?"

He can also count. For example, when he is shown a mixture of keys and pieces of cork, he can say how many keys are present, or how many pieces of cork.

He can even say how many green cups (for example) are present in a display containing cups of other colours, other green objects, or different objects of different colours. He can tell you if one object is larger or smaller than another, without having to see both at the same time.

Of course, we all know that parrots are smarter than the average bird. But even pigeons are a lot more interesting than you would expect. A standard test of self-awareness is to see if an animal understands his or her reflection in a mirror.

To test this in pigeons an experimenter put blue dots on the birds when they were anaesthetized and taught them to peck at the dots when they woke up. One dot was hidden under their bib, so they couldn't see it directly. However, when they were put in front of a mirror they saw the dot, realised where it was, and pecked at it. This would only have been possible if they had some degree of self-awareness.

Pigeons can also make sense of photographs. By creating situations in which they peck at one picture rather than another, scientists can see what kinds of distinctions they can make. It turns out that they can be trained to distinguish between pictures that contain trees and those that don't, and can recognise particular humans in a photograph, even when they are wearing different clothes.

A well-known test of spatial cognition in humans uses three shapes.

The one on one side is the same as the one in the centre, except that it has been rotated. The one on the other side is also the same, but this one has also been reflected in a mirror. Humans find it quite hard to work out which is which.

Pigeons, on the other hand, find it very easy. Unlike humans, who have to rotate the images in their minds, pigeons can see the correct answer directly.

Pigeons also have astounding memories. In one experiment, they were shown 320 human holiday slides. Two years later they were able to distinguish these pictures from similar ones which they had never seen before.

Parrots, who are at the same intellectual level as monkeys or small children, are still kept in tiny cages for human amusement, and in some countries are even eaten as food.

Chickens, who are probably at least as intelligent as pigeons, spend their entire lives in cages so small that each bird has less space than a sheet of writing paper. They live short lives of intense suffering during which all their natural instincts are frustrated.

Have a think about this next time you go down to Kentucky Fried Person.