Post-conflict affiliation between former opponents or between one of the former opponents and bystanders might have the function of conflict management, which reduces the costs associated with aggressions. One of the suggested functions of post-conflict affiliation is decreased renewed aggressions directed from aggressors to victims. However, the effect of post-conflict affiliation on renewed aggressions by victims has not been investigated. We examined whether post-conflict affiliations decreased the number of renewed aggressions initiated by winners or losers in captive bottlenose dolphins. Both winners and losers initiated renewed aggressions. However, these aggressions decreased after post-conflict affiliation between former opponents, initiated by bystanders to winners, initiated by losers to bystanders, and initiated by bystanders to losers. Post-conflict affiliation between former opponents is suggested to function as reconciliation. Post–conflict affiliation initiated by losers to bystanders is suggested to function as the protection of losers. Post-conflict affiliations initiated by bystanders to one of former opponents are suggested to function as both appeasement and protection of the opponent who affiliates with bystanders.

No abstract

In comparison with terrestrial animals, such as primates, there is limited empirical evidence for cooperative behavior in marine mammals under experimental conditions. In this study, we used a cooperative rope-pulling task to investigate how bottlenose dolphins (Tursiops truncatus) coordinate their behavior with a partner. Dolphins successfully learned and were able to perform the task, even when one subject started after the other. In the no-delay condition (i.e., both subjects sent at the same time), one pair of dolphins showed coordinated behaviors. When pairs were successful in solving the task in the delay condition (i.e., one individual sent later than the other), the initiators (i.e., first individual sent) were likely to wait for the follower to arrive, and the follower was likely to swim faster when the initiator did not wait and started pulling the rope alone. These coordinated behaviors might help resolve the given cooperative task. Our results suggest that bottlenose dolphins learn to coordinate their behaviors via trial and error and recognize the necessity of performing simultaneous actions with a partner to successfully accomplish cooperative tasks. In addition, both partners showed behavioral changes over many trials of no-delay and delay conditions, suggesting that bidirectional coordination occurred in the cooperative task.

Several terrestrial animals and delphinids manipulate objects in a tactile manner, using parts of their bodies, such as their mouths or hands. In this paper, we report that bottlenose dolphins (Tursiops truncatus) manipulate objects not by direct bodily contact, but by spontaneous water flow. Three of four dolphins at Suma Aqualife Park performed object manipulation with food. The typical sequence of object manipulation consisted of a three step procedure. First, the dolphins released the object from the sides of their mouths while assuming a head-down posture near the floor. They then manipulated the object around their mouths and caught it. Finally, they ceased to engage in their head-down posture and started to swim. When the dolphins moved the object, they used the water current in the pool or moved their head. These results showed that dolphins manipulate objects using movements that do not directly involve contact between a body part and the object. In the event the dolphins dropped the object on the floor, they lifted it by making water flow in one of three methods: opening and closing their mouths repeatedly, moving their heads lengthwise, or making circular head motions. This result suggests that bottlenose dolphins spontaneously change their environment to manipulate objects. The reason why aquatic animals like dolphins do object manipulation by changing their environment but terrestrial animals do not may be that the viscosity of the aquatic environment is much higher than it is in terrestrial environments. This is the first report thus far of any non-human mammal engaging in object manipulation using several methods to change their environment.