Yawning in wild Indo-Pacific bottlenose dolphins (Tursiops aduncus)

Yawning is defined as an involuntary behavior with breathing, characterized by a slow opening of the mouth with inhalation, followed by a maximum gaping phase, and ending with a short exhalation and closing of the mouth. Recent reports on yawning in marine mammals (common bottle-nose dolphins and a dugong) have challenged this definition because these marine mammals yawn underwater without breathing. However, yawning in marine mammals has only been studied in captive conditions, which indicates the possibility that yawning is an abnormal behavior in captive animals. Here, we report yawning in free-ranging wild Indo-Pacific bottlenose dolphins off Mikura Island, Japan. Five yawnings that occurred between 8:00 am and 10:30 am were identified from 1816 hours of video data. The dolphins in this population may exhibit more resting behaviors in the morning, which implies that yawning in this population occurred in resting states that required arousal. This is the first reported observation of yawning in Indo-Pacific bottlenose dolphins. The occurrence of yawning in a wild population suggests that it is an innate behavior, rather than abnormal behavior, in dolphins.

Automated summary

Yawning is defined as an involuntary behavior with breathing, but marine mammals can yawn without breathing. Previous studies on captive marine mammals questioned whether yawning in these mammals is abnormal. This study reports the first observation of yawning in free-ranging Indo-Pacific bottlenose dolphins, suggesting that yawning is an innate behavior in dolphins.