Dr. Jia Ning Wu, Sung Yeon Sara Ha, & Greena Kim
Dr. Joy Reidenberg
Zoo Atlanta Elephant Keepers: Scott, Steve, Nate, & Josh
Dr. Sam Rivera & Dr. Stephanie Slade
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 behavior 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 the same pressures as the human lung. Ultrasonographic imaging of the elephant sucking viscous fluids show that the elephant's nostrils dilate up to 30% in radius, which increases the nasal volume by 64%. Based on the pressures applied, we estimate that the elephants can inhale at speeds of over 150 m/s, nearly thirty times the speed of a human sneeze at 4.5 m/s. These high airspeeds 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.
In 1985 Bill Kier coined the term muscular hydrostats. Describing appendages that are purely muscular that are capable of elongation, shortening, bending, and torsion all while maintaining conservation of volume. However, the elephant trunk is unique as it has the two nasal passageways which allows the trunk to breathe and use fluid to manipulate objects.
Movie 1. The elephant uses a range of motions and techniques to pick up food. When there are groups of small items they will use suction to vacuum the food into their trunks.
Movie 2. The elephant uses suction to pick up a tortilla chip without breaking it. The chip breaks with just 5 N of force and from our models it appears the trunk is using suction at a speed of 150 m/s or 30 times the speed of a human sneeze.
Movie 3. Elephants are unique as they are one of the only species that can use fluid jets both above and below water. Here we used chia seeds to understand the flow characteristics and found the elephant drinks water at 3L/s and can store a total of nearly 9L of fluid inside their trunk. However, this amount would exceed what we see with their nasal passageway so where is that water going?
Movie 4. To store all of the fluid when drinking and vacuuming water in their trunk we see they expand their nasal passageway using the muscles inside the trunk to stretch the diameter of the nose and increase the volume by up to 60% of the total nasal volume allowing them to store 60% more water inside the trunk.
Movie 5. It turns out they can also do a combination of this to grasp objects underwater. Elephants will use the tip of their trunks and the two fingers to grasp onto objects they have suctioned and later spit out the water before eating the food suctioned into the fingers.
Image 1. From the screenshot image sequence, we can see the elephant using suction to grasp the apple underwater suspended in water filled with chia seeds to see the flow around the tip.