(Phys.org) -- A team of German and Austrian researchers has found that Grey parrots are capable of inferential reasoning on a level that is superior to virtually all other animals save great apes and humans. In lab experiments involving choosing which box contains food, the researchers describe, in their paper published in the journal Proceedings of the Royal Society B, how the birds were able to infer through auditory clues, which box contained a hidden food treat.
In this new experiment, the team built on prior research that had shown that African Grey parrots when presented with two boxes they couldnt see through, chose the box with the food in it after finding the first empty. Such an experiment showed either that the birds were avoiding the empty box, or fully believed food was hidden in the second. To get a better reading, they tried a similar experiment using sound instead of sight clues.
In the second experiment, the team showed the birds two opaque boxes, one of which contained food. The researchers then shook the boxes allowing the birds to hear that something was inside just one of them. The birds then guessed correctly which box had the food in it, walked over and tipped it over and ate their treat. Next, however, the researchers tried shaking just the empty box, producing no sound. This time, the birds were able to infer that the food must be in the other box and ran to it when given the chance, accomplishing a feat the team says, humans cant handle until the age of three. They also say that dogs and monkeys failed when given the same test and that it seems that other than the birds, only great apes and human are known to be capable of such inferential thinking.
To find out just how good the birds were at their inferential thinking, the team resorted to some trickery, they attached tiny speakers to their wrists and played recorded sounds of boxes with food being shaken instead of letting the food make the actual sound. In such cases, they found the birds could not be fooled, they picked the box with food in it only when the sound matched the boxes as they would were they to come naturally.
The researchers also found something else interesting, the birds did better when the boxes were shaken side to side, rather than up and down, likely they say, because the up and down motions of the box distracted the birds because its very similar to the way the birds normally bob their heads when interacting with one another.
Explore further: Sexual selection isn't the last word on bird plumage, study shows
More information: Grey parrots use inferential reasoning based on acoustic cues alone, PNAS, Published online before print August 8, 2012, doi: 10.1098/rspb.2012.1292
Our ability to make logical inferences is considered as one of the cornerstones of human intelligence, fuelling investigations of reasoning abilities in non-human animals. Yet, the evidence to date is equivocal, with apes as the prime candidates to possess these skills. For instance, in a two-choice task, apes can identify the location of hidden food if it is indicated by a rattling noise caused by the shaking of a baited container. More importantly, they also use the absence of noise during the shaking of the empty container to infer that this container is not baited. However, since the inaugural report of apes solving this task, to the best of our knowledge, no comparable evidence could be found in any other tested species such as monkeys and dogs. Here, we report the first successful and instantaneous solution of the shaking task through logical inference by a non-ape species, the African grey parrot. Surprisingly, the performance of the birds was sensitive to the shaking movement: they were successful with containers shaken horizontally, but not with vertical shaking resembling parrot head-bobbing. Thus, grey parrots seem to possess ape-like cross-modal reasoning skills, but their reliance on these abilities is influenced by low-level interferences.