Washington: Since most of the foods that birds eat have shells, it's hard to know what seeds and nuts are good, but this study shows that birds have their own way to determine the quality of the food inside of the shell.
The study by research team from Poland and Korea suggests that the Mexican Jays (Aphelocoma wollweberi) may be able to "weigh" peanuts and maybe even "listen to" peanuts while handling them in their beaks.
Sang-im Lee, Piotr Jablonski, Maciej and Elzbieta Fuszara, the leading researchers in this study, together with their students and helpers, 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).
Sang-im Lee of Seoul National University said that when they presented the jays with ten empty and ten full identically looking pods (pods without or with three nuts inside), the researchers noticed that after picking them up the birds rejected the empty ones and accepted the full peanuts, without opening them.
The researchers used slow motion videos to see what happens when the bird is deciding whether to drop or take away the peanut pod and found out that birds shake the nuts in their beaks.
When they shake the nuts in their beaks, the birds produce sounds by opening and closing their beaks around the peanut shell for brief moments. The researchers think that the jays also take this sound into account.
Lee and Jablonski concluded that their next goal is to disentangle the role of sound relative to the perception of "heaviness" and to determine if jays use the same sensory cues for acorns, their natural food.
The study is published in Journal of Ornithology.