Bird-brained pigeons understood concepts of space and time long before the birth of Albert Einstein, scientists have shown.
But they figure out the abstract ideas using a different part of the brain than that employed by the famous physicist, and other humans.
In a series of experiments, pigeons were shown a static horizontal line on a computer screen and had to judge its length or the amount of time it was visible.
The birds correctly worked out that longer lines had longer duration - and also lines that were visible for longer were longer in length.
What this means is that pigeons appear to use a common area of the brain to judge space and time, and do not process the concepts separately, said the researchers.
Einstein also saw space and time as non-separate, coming up with the revolutionary notion of a single space-time continuum.
Lead scientist Professor Edward Wasserman, from the University of Iowa, US, who has spent four decades studying intelligence in pigeons, crows, baboons and other animals, said: "The cognitive prowess of birds is now deemed to be ever closer to that of both human and nonhuman primates.
"Those avian nervous systems are capable of far greater achievements than the pejorative term 'bird brain' would suggest."
Humans perceive space and time using the parietal cortex, which is part of the cerebral cortex, the brain's outermost layer.
The cerebral cortex is known to be the centre of higher mental processes, including speech and decision-making.
In the first of the tests, pigeons were shown a horizontal line either 6cm or 24cm long for either two or eight seconds.
If they correctly reported the length or duration of the line - by pecking one of four visual symbols - they received a food reward.
The tests then became trickier, with the researchers introducing additional line lengths that were presented for shorter or longer lengths of time.
The findings are reported in the journal Current Biology.
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