In a new study, published in the Journal of Ornithology, an international team of researchers from Poland and Korea found that some birds have the ability to choose the best quality nuts without even opening their shells.

The interesting study was carried out in Arizona, wherein researchers revealed that the Mexican Jays (Scientific name Aphelocoma wollweberi) were able to 'weigh' peanuts and even 'listen to' them, while handling them with their beaks.

The study involved presenting the bird with ten empty and ten full identically looking pods. It was found that after picking the nuts up with their beaks, the birds rejected the empty ones and accepted the full peanuts, without even opening them. Another experiment with identical looking normal nuts and nuts that were 1g heavier confirmed that, jays were able to tell the difference between the heavier nuts.

The researchers also brought in few alterations to the above, wherein they opened one type of pods that contained three nuts, removed two out of these three and closed the shell again. The second type of pods was the one that normally contained just one nut. When the birds were tested on these two pods, containing nuts of similar content but having different mass as a whole, the birds intelligently chose the latter. This made the researchers conclude that the birds figured out that the larger pods did not weigh as much as they otherwise should and therefore, they preferred the smaller pods, which weighed as expected for their size.

The entire feeding activity of the birds was captured using slow motion cameras. The researchers said that, "We found out that birds shake the nuts in their beaks. We think that these movements may provide them with the information generally similar to our feeling of 'heaviness' when we handle an object in our hands." They also felt that the Jays considered the noise the nuts made, to make their choice.