Whales, marine mammals, spend their entire lives submerged in the ocean’s depths. Their behaviors, particularly during the nighttime hours, are a subject of ongoing scientific study, revealing adaptations to their aquatic world. Understanding what these creatures do once darkness falls provides insight into their lives beneath the waves.
How Whales Sleep
Whales exhibit unique sleeping patterns adapted to their aquatic environment. Many whale species engage in unihemispheric slow-wave sleep (USWS), a state where one half of their brain rests while the other half remains active. This adaptation allows them to maintain essential bodily functions, such as surfacing to breathe and remaining vigilant for potential threats in their surroundings.
During USWS, one eye often remains open while the other is closed, corresponding to the active and resting brain hemispheres. This partial awareness enables them to react to changes in their environment or the presence of predators. Dolphins, a type of toothed whale, have been observed swimming slowly in a synchronized fashion during this state, maintaining group cohesion and minimizing energy expenditure.
Different whale species adopt various postures for sleeping. Some, like sperm whales, are known to “log,” floating vertically just beneath the surface, appearing almost motionless in the water. Other species may sleep horizontally at the surface or while swimming slowly, maintaining a level of buoyancy that prevents them from sinking.
Nighttime Activities
Beyond periods of rest, whales engage in a range of activities at night, often driven by foraging opportunities. Many toothed whales, such as sperm whales, undertake deep dives at night to hunt for prey like colossal and giant squid, which migrate closer to the surface during these hours. These hunts can extend to depths of several hundred meters.
Baleen whales, including blue whales and fin whales, may also continue feeding at night, consuming vast quantities of krill and small schooling fish. These prey species often exhibit diel vertical migration, ascending to shallower waters at night, making them more accessible for filter-feeding whales.
Social interactions, such as communication and group coordination, also persist into the night. Whales use an array of vocalizations, including clicks, whistles, and moans, to communicate with one another over long distances. These acoustic signals are important for maintaining group cohesion, coordinating movements, and potentially for mating behaviors.
Navigating the Darkness
Whales possess sensory systems that enable them to navigate and perceive their environment effectively in darkness. Toothed whales primarily rely on echolocation, a biological sonar system, to orient themselves and locate objects. They emit high-frequency clicks from an organ called the melon, located in their forehead.
These sound waves travel through the water, bounce off objects, and return as echoes, which are then received by specialized structures in the whale’s lower jaw. The brain processes these echoes, creating an acoustic map of their surroundings, allowing them to pinpoint prey, detect obstacles, and navigate complex underwater terrains with precision. This system is important during deep dives where vision is limited.
Baleen whales, while not using echolocation in the same way as toothed whales, possess an acute sense of hearing that is important for their nighttime existence. They can detect low-frequency sounds over vast distances, which aids in long-range communication, finding mates, and tracking prey concentrations. Additionally, their sense of touch and pressure perception through their skin and specialized vibrissae (sensory hairs) provide supplementary information about their immediate environment.