Elephant trunks have evolved from the nose and upper lip in the course of evolution. With the characteristic body part, the animals can do amazing things: they breathe or smell with it, but at the same time they can also feel, suck and grasp. Researchers have now analyzed how elephants move various types of food with their proboscis. They hope that their findings may be of interest to technical developments such as robotic arms.

The unusual thing about their analysis is that the finer the food, the more force the animals have to use with their proboscis. This is a nuisance, as the team led by David Hu from the Georgia Institute of Technology, Atlanta, reports in the Journal of the Royal Society Interface.

"Wild African elephants are voracious eaters who consume 190 grams of food per minute or the weight of two corncobs," the authors write. An elephant can eat up to 18 hours a day and therefore need an efficient food intake. Hu and colleagues therefore explored the unique method by which elephants squeeze their food before moving it with the trunk to the mouth.

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The scientists used a force plate on which they placed food of various sizes. Turnips and carrots cubes with the edge lengths 32, 16 and 10 millimeters as well as wheat bran and grains with an average size of two millimeters. The force plate stood on the cage so that the African elephant in the zoo of Atlanta had to access with his trunk obliquely to the food. African elephants have two appendages at the point of the trunk, with which they can grasp objects.

DPA / Jianing Wu / JRSoc.Interface

Proboscis technique with different food sizes

If the elephant took the largest, easier-to-grasp pieces, the trunk reaching diagonally out of the cage remained straight. On the smaller pieces, which required more effort to squeeze and grasp, the animal used a trick: it bent the trunk down vertically so that it stood like a pillar on the food. In this way they can increase the pressure on the food - also because the weight of the bent part of the trunk is additionally loaded on the plate.

The elephant set the kink in the trunk all the higher, the more fragmented the food was: in the 16-millimeter pieces, it was on average 3.9 centimeters high, in the fine wheat bran, however, eleven centimeters high.

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For the smaller food, which needed to be compressed harder not to fall off, the animal exerted the greatest power on the pressure plate: in the wheat bran it was about 48 Newton, in the largest pieces, however, only seven Newton. The researchers suspect that this is the least force that the elephant can deliberately exercise with its trunk. By comparison, an object weighing one kilogram exerts a force of about ten Newton on the ground.

In particular, since Hu and several other team members are engineers, they see the technical applicability of their findings: "In the future, heavy robotic manipulators can also bend to hold objects together and lift them in groups," they write.

Scientists have been trying for a long time to identify clever techniques in plants and animals that could be used for technical development. For example, bionics researchers have already analyzed how giant manta rays filter food from the sea or why coconuts are so extraordinarily stable.