Dolphins Sleep with One Half of Their Brain at a Time

Dolphins can stay alert and active for 15 days or more by sleeping with one half of their brain at a time, scientists have learned.

The trick of keeping half the brain continuously awake is vital to the sea mammals’ survival, experts believe.
It allows them to come to the surface every so often to breath, and remain constantly vigilant for sharks.

Scientists in California, US, tested the ability of two bottlenose dolphins to echolocate accurately over periods of time which would have left other animals sleep-deprived and exhausted.

The dolphins, a male called Nay and female called Say, had to swim around a pen looking for phantom sonar targets.

Each of the eight targets consisted of a device that picked up dolphin sound pulses and sent back ”phantom” echoes.

When a dolphin detected an echo from an activated target, it responded by pressing a paddle. Correct detection triggered a tone, signalling success, and the dolphin was rewarded with a fish. False alarms led to no tone and no reward.

Over three sessions of five continuous days both dolphins did well, with success rates of up to 99%, but Say outperformed her male partner.

The scientists then went on to test Say further by repeating the same experiment over a period of 30 days. In the event, a storm cut the trial short after 15 days had elapsed. However, during this time Say’s performance hardly deteriorated at all.

The findings were published yesterday in the online journal Public Library of Science ONE.

Lead researcher Dr Brian Branstetter, from the National Marine Mammal Foundation in San Diego, said: “These majestic beasts are true unwavering sentinels of the sea. The demands of ocean life on air breathing dolphins have led to incredible capabilities, one of which is the ability to continuously, perhaps indefinitely, maintain vigilant behaviour through echolocation.”

The difference in performance between Nay and Say was probably down to personality, said the scientists.

Say appeared much more motivated and keen on the task, often producing “victory squeals” when she correctly responded to a target.

Dolphins use their sonar-like ability to navigate, find prey, detect predators, and co-ordinate group behaviour.

Brain wave measurements have confirmed that the creatures are capable of “unihemispheric sleep” – sleeping with just one side of the brain. When dolphins sleep in this way, they often keep one eye open.

Many dolphin populations are exposed to almost constant risk of shark attack, and the animals commonly carry bite marks, said the researchers. Continually listening to their echo signals allowed them to counter the shark threat, even in murky waters.

The scientists wrote: “From an anthropomorphic viewpoint, the ability of the dolphin to continuously monitor its environment for days without interruption seems extreme.However, the biological, sensory and cognitive ecology of these animals is relatively unique and demanding. If dolphins sleep like terrestrial animals, they might drown. If dolphins fail to maintain vigilance, they become susceptible to predation. As a result, the apparent ‘extreme’ capabilities these animals possess are likely to be quite normal, unspectacular, and necessary for survival from the dolphin’s perspective.”

Dolphins can stay alert and active for 15 days or more by sleeping with one half of their brain at a time, scientists have learned . . .

Follow Us On Google News | Get Our Newsletter



Trending News on PVDN

  • tropical-storm-flossie-hurricane-mexico-pacific-coastTropical Storm Flossie to Strengthen into Hurricane as It Tracks Along Mexico’s Pacific Coast Tropical Storm Flossie is expected to become a Category 2 hurricane by July 2 as it moves parallel to Mexico’s Pacific coast, bringing dangerous rainfall, wind, and surf. Tropical Storm Flossie is on the verge of forming from Tropical Depression Six-E and is forecast to strengthen rapidly into a hurricane as it parallels Mexico’s southwestern…
  • hurricane-flossie-strengthens-july-1-2025Hurricane Flossie will bring tropical storm conditions to parts of Guerrero, Michoacán, Colima, and Jalisco Hurricane Flossie intensifies off Mexico's Pacific coast with winds near 90 mph. Heavy rain, flooding, and tropical storm conditions expected in parts of Guerrero, Michoacán, Colima, and Jalisco. Hurricane Flossie continued to intensify early Tuesday morning as it moved west-northwestward off the coast of southwestern Mexico, prompting tropical storm warnings and watches across multiple states.…
  • tropical-storm-flossie-mexico-coast-rain-surf-alertCabo Corrientes under tropical storm watch as Flossie expected to Bring Heavy Rain and Dangerous Surf to Southwestern Mexico Tropical Storm Flossie is forecast to strengthen and may impact Mexico's southwest coast from Zihuatanejo to Cabo Corrientes with heavy rain, flooding, and hazardous surf early this week. Tropical Storm Flossie is expected to deliver heavy rains, gusty winds, and dangerous surf conditions to Mexico’s southwestern coast in the coming days, prompting authorities to issue…
  • puerto-vallarta-rainfall-hurricane-flossie-july-2025Puerto Vallarta braces for torrential rains as Hurricane Flossie gains strength Puerto Vallarta faces a high risk of flooding as Hurricane Flossie intensifies in the Pacific. Torrential rains and overwhelmed drainage systems pose major challenges for the city. Puerto Vallarta, a city wedged between the Sierra Madre mountains and the Pacific Ocean, is no stranger to dramatic weather shifts—but this summer, the skies are testing the…
  • tropical-storm-flossie-strengthens-mexico-june-2025Tropical Storm Flossie Strengthens Off Mexico’s Pacific Coast, Could Become Hurricane by Tuesday Tropical Storm Flossie gains strength off southwestern Mexico, with hurricane status possible by Tuesday. Storm warnings issued from Punta San Telmo to Playa Perula. Tropical Storm Flossie continues to gain strength off Mexico’s Pacific coastline, prompting tropical storm warnings and watches across several southwestern states. According to the National Hurricane Center (NHC), Flossie is expected…
  • raw-sewage-playa-los-muertos-puerto-vallartaMore Raw Sewage Dumping at Playa Los Muertos Appear to Come From Local Hotel Business owners in Puerto Vallarta are demanding action after raw sewage was discovered leaking onto Playa Los Muertos, raising public health and tourism concerns. A raw sewage leak at Playa Los Muertos in Puerto Vallarta has sparked outrage among local tourist service providers and business owners, who say the contamination is driving away visitors and…
  • cancun-beach-cleanup-sargassumMassive Beach Cleanup to Combat Sargassum in Cancun After a week of the Cancun’s tourism department denying sargassum existed and insisting media photos were fakes, over 600 public servants and volunteers joined the first simultaneous beach cleanup. In a bold step toward environmental preservation and tourism sustainability, Cancun's Municipal President Ana Paty Peralta led the city’s first simultaneous beach cleanup effort this week.…
  • oregon-murder-fugitive-extradited-puerto-vallartaFugitive Wanted for 2008 Oregon Homicide Captured in Puerto Vallarta and Extradited to U.S. Jesús Rodríguez Borrayo, a fugitive for 17 years, was extradited from Mexico to Oregon for his role in a 2008 drive-by shooting that left one dead. He was located in Puerto Vallarta. A man wanted for murder and other violent crimes in the United States for nearly two decades has been extradited after being found…
  • cancun-2025-sargassum-beaches-and-activitiesSargassum won’t ruin your Cancun vacation, there are plenty of clean beaches and tourist activities As the 2025 sargassum season continues through September, visitors to Cancun can still enjoy clear beaches like Playa Delfines and Playa Caracol. As the 2025 sargassum season intensifies across Quintana Roo, tourists are finding it more difficult to enjoy the region’s iconic white-sand beaches without encountering the unsightly brown seaweed. While the influx of sargassum…
  • tropical-wave-7-floods-bacalar-chetumal-emergency-responseTropical Wave Floods Bacalar and Chetumal as Navy and Army Activate Emergency Plans Torrential rains from Tropical Wave 7 flood Bacalar and Chetumal, prompting emergency response from the Navy and Army. Several towns remain isolated in southern Quintana Roo. Torrential rains caused by Tropical Wave Number 7 have flooded multiple communities in southern Quintana Roo, prompting a joint emergency response from Mexico’s Navy and Army. Authorities activated their…
Scroll to Top