Social object play between captive bottlenose and Risso's dolphins.

Many animal species engage in social object play with movable objects. Two bottlenose dolphins (Tursiops truncatus) and one Risso's dolphin (Grampus griseus) owned by the Kujukushima Aquarium, Japan, occasionally shared and played with an object. Herein, we report social object play between two dolphins exchanging a ball in water. Just before delivery of the ball, one dolphin made an action to request the ball from the dolphin that possessed the ball. This request behavior is also discussed in this report. This study is the first to report two different cetacean species engaging in social object play with one object.