Dolphins frequently leap above the water surface, this being done for various reasons. When travelling, jumping can save the dolphin energy as there is less friction while in the air.[65] This type of travel is known as porpoising.[65] Other reasons include orientation, social displays, fighting, non-verbal communication, entertainment and attempting to dislodge parasites.[66][67]
Dolphins show various types of playful behavior, often including objects, self-made bubble rings, other dolphins or other animals.[68][8][69] When playing with objects or small animals, common behavior includes carrying the object or animal along using various parts of the body, passing it along to other members of the group or taking it from another member, or throwing it out of the water.[68] Dolphins have also been observed harassing animals in other ways, for example by dragging birds underwater without showing any intent to eat them.[68] Playful behaviour that involves an other animal species with active participation of the other animal can also be observed however. Playful human interaction with dolphins being the most obvious example, however playful interactions have been observed in the wild with a number of other species as well, such as Humpback Whales and dogs.[70][71]
Sleeping
Further information: Sleep (non-human)
Sleeping dolphin in captivity: a tail kick reflex keeps the dolphin's blowhole above the water
Generally, dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, thus maintaining enough consciousness to breathe and to watch for possible predators and other threats. Earlier sleep stages can occur simultaneously in both hemispheres.[72][73][74] In captivity, dolphins seemingly enter a fully asleep state where both eyes are closed and there is no response to mild external stimuli. In this case, respiration is automatic; a tail kick reflex keeps the blowhole above the water if necessary. Anesthetized dolphins initially show a tail kick reflex.[75] Though a similar state has been observed with wild sperm whales, it is not known if dolphins in the wild reach this state.[76] The Indus river dolphin has a sleep method that is different from that of other dolphin species. Living in water with strong currents and potentially dangerous floating debris, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds
Dolphins show various types of playful behavior, often including objects, self-made bubble rings, other dolphins or other animals.[68][8][69] When playing with objects or small animals, common behavior includes carrying the object or animal along using various parts of the body, passing it along to other members of the group or taking it from another member, or throwing it out of the water.[68] Dolphins have also been observed harassing animals in other ways, for example by dragging birds underwater without showing any intent to eat them.[68] Playful behaviour that involves an other animal species with active participation of the other animal can also be observed however. Playful human interaction with dolphins being the most obvious example, however playful interactions have been observed in the wild with a number of other species as well, such as Humpback Whales and dogs.[70][71]
Sleeping
Further information: Sleep (non-human)
Sleeping dolphin in captivity: a tail kick reflex keeps the dolphin's blowhole above the water
Generally, dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, thus maintaining enough consciousness to breathe and to watch for possible predators and other threats. Earlier sleep stages can occur simultaneously in both hemispheres.[72][73][74] In captivity, dolphins seemingly enter a fully asleep state where both eyes are closed and there is no response to mild external stimuli. In this case, respiration is automatic; a tail kick reflex keeps the blowhole above the water if necessary. Anesthetized dolphins initially show a tail kick reflex.[75] Though a similar state has been observed with wild sperm whales, it is not known if dolphins in the wild reach this state.[76] The Indus river dolphin has a sleep method that is different from that of other dolphin species. Living in water with strong currents and potentially dangerous floating debris, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds
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