New York, May 25 (IANS): Just like humans, birds too can choose the best quality peanuts without even opening their shells, says a recent research.

Mexican Jays (Aphelocoma wollweberi) distinguish between heavier and lighter peanuts by shaking the nuts in their beaks, which allows them to 'feel' nut heaviness, the findings showed.

"When we presented the jays with ten empty and ten full identically looking pods (pods without or with three nuts inside), we noticed that after picking them up, the birds rejected the empty ones and accepted the full peanuts, without opening them," said corresponding author of the study Sang-im Lee of Seoul National University, South Korea.

The study was carried out in Arizona in the US by an international research team from Poland and South Korea. The researcher spent many hours delicately opening shells of hundreds of peanuts, changing the contents and then presenting them to the jays in order to see if the birds can figure out the differences in the content of identically looking peanut pods (peanuts in shell).

A series of similar experiments with similar looking normal nuts and nuts that were one gram heavier (pods with some clay added) confirmed that jays always were able to distinguish and preferred the heavier nuts.

"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," Piotr Jablonski from Seoul National University pointed out.

The study was published in the Journal of Ornithology.