Digestion and any other processes have to wait.įinally, these animals have a higher tolerance for carbon dioxide (CO 2). And when diving, marine mammals' blood travels only to the parts of the body that need oxygen-the heart, the brain and the swimming muscles. Their red blood cells also carry more oxygen. In addition, they exchange more air with each inhalation and exhalation. Marine mammals can take in more air with each breath, as their lungs are proportionately larger than those in humans.
Other methods help marine mammals to hold their breath longer than other types of mammals can. But equipped with a voluntary respiratory system, whales and dolphins must keep part of the brain alert to trigger each breath. Humans, of course, can breathe while the conscious mind is asleep our subconscious mechanisms have control of this involuntary system. Although still a matter of discussion, most researchers feel that in order to breathe, a dolphin or whale must be conscious and alert to recognize that its blowhole is at the surface.
The blowhole is a flap of skin that is thought to open and close under the voluntary control of the animal. To avoid drowning during sleep, it is crucial that marine mammals retain control of their blowhole. But a pilot whale was noted as having six minutes of REM in a single night. Rapid Eye Movement (REM)-a characteristic of deep sleep-is hard to discern. It is not clear whether cetaceans undergo dream sleep. Bottlenose dolphins, based on electroencephalogram (EEG) readings, spend an average of 33.4 percent of their day asleep. This pattern is often called cat-napping.ĭolphins generally sleep at night, but only for a couple hours at a time they are often active late at night, possibly matching this alert period to feed on fish or squid, which then rise from the depths. After approximately two hours, the animal will reverse this process, resting the active side of the brain and awaking the rested half. It also signals when to rise to the surface for a fresh breath of air. This attentive side is used to watch for predators, obstacles and other animals. The other half of the brain stays awake at a low level of alertness. While sleeping, the bottlenose dolphin shuts down only half of its brain, along with the opposite eye. They may rest in the same general area, or companionable animals may pair for sleeping while swimming. Adult male dolphins, which generally travel in pairs, often swim slowly side by side as they sleep. Lots of swimming will tire an infant, producing a weak animal susceptible to infection or attack. If she does for any length of time, the calf will begin to sink it is not born with enough body fat or blubber to float easily.
In fact, she cannot stop swimming for the first several weeks of a newborn's life. At these times, the mother will also sleep on the move. Young whales and dolphins actually rest, eat and sleep while their mother swims, towing them along in her slipstream-a placement called echelon swimming. When marine mammals sleep and swim at once, they are in a state similar to napping. It is called logging because in this state, a dolphin resembles a log floating at the water's surface. Individual dolphins also enter a deeper form of sleep, mostly at night. So how can they sleep and not drown? Observations of bottlenose dolphins in aquariums and zoos, and of whales and dolphins in the wild, show two basic methods of sleeping: they either rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal. Marine mammals such as whales and dolphins spend their entire lives at sea.