May 23, 2015
Cracking a nut is difficult, so how do animals make sure that they don’t waste effort on a snack that winds up being tiny or rotten?
In research published recently in the Journal of Ornithology, an international team led by experts from the Seoul National University’s Laboratory of Behavioral Ecology and Evolution watched a group of Mexican Jays (Aphelocoma wollweberi) living in Arizona to see how they selected nuts from a feeder and if they had any tricks that helped them avoid getting bad ones.
They found that the birds may be able to “weigh” nuts, and possibly even “listen” to them as they handle the nuts in their beaks. The study authors spent several hours observing the behavior of the jays as they delicately broke open the shells of hundreds of peanuts, changing the contents and presenting them to the birds to see if the creatures could tell the difference.
Sound plays a role in the evaluation process
The researchers conducted a series of experiments, including one in which some of the peanuts presented to the jays were empty. Even though the pods looked identical on the outside, “we noticed that after picking them up the birds rejected the empty ones and accepted the full peanuts, without opening them,” said corresponding author Dr. Sang-im Lee of Seoul National University.
In another experiment, the birds were presented with two different nuts that looked the same, but had a one gram difference in weight. This revealed that the jays were able to distinguish between the two, and they favored the heavier nuts.
Researchers then took peanuts of different sizes and equalized their weight. The authors found that jays preferred the smaller peanuts, even though the two pods weighed the same. Researcher Dr. Elzbieta Fuszara explained that the birds could tell that the larger pods did not weigh as much as they should and rejected them on this basis.