If you've ever been described as "birdbrained," don't feel bad; it's not as much of an insult as you might think. A study out of Seoul National University revealed that some birds have mastered a surprising trick that helps them make the most of their trips to the feeder. The birds in the study demonstrated the ability to distinguish heavier peanuts from lighter ones, even when the peanuts were still in the shell. 

That's right, much like we turn into amateur weightlifters when we're appraising tomatoes and melons in the produce section, birds (or at least the Mexican jays in the study) take time to make sure they've gotten the most bang for their beak.

"When we presented the jays with 10 empty and 10 full 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 Dr. Sang-im Lee.

Birds have feathers, not scales, so how were they able to complete their evaluation? "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," explained Dr. Piotr Jablonski.

The authors of the study believe that the birds not only were able to discern the difference in weights between the full and empty shells, but also relied on the sounds that were produced when peanuts rattled inside their shells. However, more research is needed to nail down the role of sound in the birds' decision-making processes.

This study provides further evidence that, as a group, birds should not be underestimated. About a decade ago, they threatened to wipe out the human race through the spread of avian flu (though they eventually chose to spare us, in their infinite compassion). Earlier this year, Michael Keaton helped them make their presence felt at the Oscars (where they did some damage control for Alfred Hitchcock's smear campaign). Now that they seemingly have the concept of weight down pat, maybe they'll develop a new alternative to the metric system, or hold nationally televised World's Strongest Bird competitions. Whatever the future holds, it's clear that they've come a long way in maximizing their talons.  

Read more at EurekAlert, and watch Alan Weisman, author of The World Without Us, talk about how his early experiences with birds inspired his work.