Yawning is an involuntary action that begins with a slow opening of the mouth with inhalation, followed by a maximum gaping phase, and ends with a short exhalation and the closing of the mouth. A wide variety of vertebrate species, including humans, yawn. Here, we report underwater yawn-like behavior in three captive common bottlenose dolphins, inferred from 119-h of observations. Five cases of yawn-like behavior were selected out of 2045 open-mouth behaviors, after removing intentional open-mouth behaviors. Yawn-like behaviors were chosen that had a mouth open–close duration ratio of ≤ 1 (duration of Phase 3, the period of mouth closing after maximum opening, divided by the duration of Phase 1, the period of mouth opening from start to maximum opening). Naïve human evaluators selected “yawn-like” behaviors. All five cases of yawn-like behavior occurred during inactive periods, similar to human yawns. In three of the five cases, inactivity levels significantly decreased within 4 min after the yawn-like behavior; therefore, yawn-like behavior in dolphins may increase their arousal level in drowsy states. Thus, the yawn-like behavior of dolphins, without breathing, is similar to yawning in terrestrial animals, including humans.

打哈欠是一种不自觉的动作，开始时缓慢张嘴吸气，然后是最大的张开阶段，最后是短暂的呼气和嘴巴的闭合。包括人类在内的多种脊椎动物都会打哈欠。在这里，我们报告了三只圈养的普通宽吻海豚在水下打哈欠的行为，这是从 119 小时的观察中推断出来的。在去除有意的张嘴行为后，从 2045 次张嘴行为中选出了 5 例类似打哈欠的行为。选择嘴巴张合持续时间比≤1的打哈欠类行为（第3阶段的持续时间，最大张开后嘴巴闭合的时间，除以第1阶段的持续时间，从开始到最大张嘴的时间）开）。天真的人类评估者选择了“类似打哈欠”的行为。所有 5 例类似哈欠的行为都发生在非活动期，类似于人类的哈欠。在五个案例中的三个中，在打哈欠样行为后 4 分钟内，不活动水平显着下降；因此，海豚的打哈欠行为可能会增加它们在昏昏欲睡状态下的唤醒水平。因此，没有呼吸的海豚打哈欠的行为类似于陆生动物（包括人类）的打哈欠。