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. 2021 Jun;18(179):20210215.
doi: 10.1098/rsif.2021.0215. Epub 2021 Jun 2.

Suction feeding by elephants

Andrew K Schulz  1 , Jia Ning Wu  1 , Sung Yeon Sara Ha  1 , Greena Kim  1 , Stephanie Braccini Slade  2 , Sam Rivera  3 , Joy S Reidenberg  4 , David L Hu  1   5
Affiliations

Suction feeding by elephants

Andrew K Schulz et al. J R Soc Interface. 2021 Jun.

Abstract

Despite having a trunk that weighs over 100 kg, elephants mainly feed on lightweight vegetation. How do elephants manipulate such small items? In this experimental and theoretical investigation, we filmed elephants at Zoo Atlanta showing that they can use suction to grab food, performing a behaviour that was previously thought to be restricted to fishes. We use a mathematical model to show that an elephant's nostril size and lung capacity enables them to grab items using comparable pressures as the human lung. Ultrasonographic imaging of the elephant sucking viscous fluids show that the elephant's nostrils dilate up to [Formula: see text] in radius, which increases the nasal volume by [Formula: see text]. Based on the pressures applied, we estimate that the elephants can inhale at speeds of over 150 m s-1, nearly 30 times the speed of a human sneeze. These high air speeds enable the elephant to vacuum up piles of rutabaga cubes as well as fragile tortilla chips. We hope these findings inspire further work in suction-based manipulation in both animals and robots.

Keywords: muscular hydrostat; object manipulation; suction.

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Figures

Figure 1.
Figure 1.
An elephant uses suction to pick up lightweight objects. (a) The trunk of an African elephant, showing its two prehensile ‘fingers’ at the tip of the trunk. Scale bar, 5 cm. (b) A regime diagram for suction across number and size of food items. The red symbols indicate the use of suction and black symbols indicate the absence of suction. The cube-shaped objects are rutabaga cubes and the circular object is a tortilla chip. (c) Elephant picking up ten 16 mm rutabaga cubes using suction. (d) Elephant using suction to levitate a tortilla chip into its grip. (e) Elephant pressing its trunk against a tortilla chip and applying suction to pick it up.
Figure 2.
Figure 2.
Suction of water. (a) Side view of the elephant siphoning a solution of water mixed with chia seeds acting as flow tracers. Points closest to the nostrils experience the highest speed flow as shown by the trajectory of the chia seeds. Scale bar, 5 cm. (b) Bottom view of elephant siphoning water and closing the trunk to hold the water. Scale bar, 3 cm. (c) Time course of the water flow rate Q. Closed points indicating mean values, and shaded regions show standard deviation. (d) Schematic of a elephant trunk applying suction to a flat object of mass mt. The red arrows denoted the direction of flow. Nostrils of radius a generate a pressure of P0, which generates a flow u0 in the nasal cavity, and a flow u outside the trunk which rapidly decays with distance L.
Figure 3.
Figure 3.
Measurement of nasal wall diameter by ultrasonographic imagery. (a) Set-up for ultrasonographic measurement. (b) Schematic diagram of ultrasonographic measurements collection site. Illustrated by B. Seleb. (c) Ultrasonic image of nasal wall during suction of water. Scale bar, 1 cm. (d) Ultrasonic image of suction of bran water. Scale bar, 1 cm. (e) Relationship between nasal radius r and density of fluid inhaled.
Figure 4.
Figure 4.
Predicted suction feeding across terrestrial animals. (a) Relationship between nostril radius and body mass, with power law fit shown by the red line. (b) Relationship between body mass and the theoretical distance Lc to pick up a tortilla chip. Animal portraits from Adobe Creative Studio.
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