About us: We own the Wild Birds Unlimited nature shop in East Lansing, Michigan,
a store that provides a wide variety of supplies to help you enjoy the birdwatching hobby.

This blog was created to answer frequently asked questions & to share nature stories and photographs.
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Wednesday, November 6, 2019

How birds choose a nut

Many animals feed on seeds, acorns or nuts with shells.  How do the animals know how much and what quality of food is hidden inside?
For birds that cache food items for later, a new study published in Journal of Ornithology suggests that some birds may be able to "weigh" peanuts and maybe even "shake" peanuts while handling them in their beaks to determine the quality. Drs. 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).

"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." says Dr. Sang-im Lee of Seoul National University. A series of similar experiments with identically looking normal nuts and nuts that were 1g heavier (pods with some clay added) confirmed that jays always were able to distinguish and preferred the heavier nuts.

In another experiment the researchers prepared one type of peanut pods by opening the shell, removing two out of the three nuts and closing the shell again. The second type of pod was prepared by opening a small pod, which normally contains only one nut, and closing it. "The jays figured out that the larger pods did not weigh as much as they should and the birds preferred the smaller pods, which weighed as expected for their size," comments Dr. Fuszara. They behaved as if they knew that "something is wrong" with the larger nuts.

So how do they know it? 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. "Our 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," conclude Dr. Lee and Dr Jablonski.

Story Source:
Materials provided by Laboratory of Behavioral Ecology and Evolution at Seoul National University.

Journal Reference:
  1. Piotr G. Jablonski, Sang-im Lee, Elzbieta Fuszara, Maciej Fuszara, Choongwon Jeong, Won Young Lee. Proximate mechanisms of detecting nut properties in a wild population of Mexican Jays (Aphelocoma ultramarina). Journal of Ornithology, 2015; DOI: 10.1007/s10336-015-1193-6

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