Suction feeding by elephants.

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.

Elephant trunks form joints to squeeze together small objects.

Wild African elephants are voracious eaters, consuming 180 g of food per minute. One of their methods for eating at this speed is to sweep food into a pile and then pick it up. In this combined experimental and theoretical study, we elucidate the elephant's unique method of picking up a pile of food by compressing it with its trunk. To grab the smallest food items, the elephant forms a joint in its trunk, creating a pillar up to 11 cm tall that it uses to push down on food. Using a force sensor, we show the elephant applies greater force to smaller food pieces, in a manner that is required to solidify the particles into a lump solid, as calculated by Weibullian statistics. Elephants increase the height of the pillar with the force required, achieving up to 28% of the applied force using the self-weight of the pillar alone. This work shows that elephants are capable of modulating the force they apply to granular materials, taking advantage of their transition from fluid to solid. In the future, heavy robotic manipulators may also form joints to compress and lift objects together.

Behavioral changes following alterations in the composition of a captive bachelor group of western lowland gorillas (Gorilla gorilla gorilla).

Western lowland gorillas (Gorilla gorilla gorilla) in zoos are housed in family or bachelor groups to maximize social opportunities. While wild bachelor groups are transient, all-male groups in zoos may be maintained for many years. Captive bachelor groups need to be carefully monitored, particularly during periods of demographic transition, due to the possibility for escalating aggression. We examined behavioral changes in a bachelor group at the Saint Louis Zoo following two significant alterations in group composition: (1) the introduction of two immature related males in 2011 and (2) the death of the dominant silverback in 2015. Behavioral data were collected on group members using 15 min focal observations with 30-s instantaneous scans, totaling 185.25 hr for the first transition and 115.25 hr for the second transition (with equal effort in baseline and transition periods). We found that the addition of the two subadult males resulted in a significant increase in affiliation in the group often initiated by these new younger individuals, while the rate of abnormal and aggressive behavior did not change significantly. The rate of abnormal, aggressive, or affiliative behavior in the group also did not change significantly following the death of the dominant silverback. Overall, we conclude that this bachelor group and potentially others can endure possibly destabilizing social transitions and remain cohesive social units. Behavioral changes will result from transitions, but the effect on individuals or impact on the group will vary. Therefore, longitudinal monitoring of bachelor groups will be essential for effective management during any major changes.