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

  • puerto vallarta lettersPuerto Vallarta needs a new image to create meaningful reasons for travelers to visit Business leaders at Jalisco Tourism Secretariat forums stressed the need for renewing Puerto Vallarta image and diversifying attractions to appeal to national and international markets. Local business leaders and tourism specialists agreed this week that Puerto Vallarta needs a fresh look and a broader range of attractions to compete at home and abroad. In a…
  • protests3Mexico City Protests: There is a fine line between anti-gentrification and xenophobia The line between anti-gentrification and racism is clear if you choose to see it: genuine activism targets policy and practice, not nationality or ethnicity. I have lived in Mexico for two decades, and I have never witnessed the level of anti-American sentiment that exists today. All of it is tied to the buzzword "gentrification," a…
  • 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…
  • puerto-vallarta-police-chase-bahia-de-banderasPuerto Vallarta police chase ends in deadly collision in Bahía de Banderas A Puerto Vallarta police chase along Highway 200 ended in a deadly collision in Bahía de Banderas, leaving two people dead. A high-speed chase that began in Puerto Vallarta, Jalisco, and ended in Bahía de Banderas, Nayarit, left at least two people dead and raised new questions about police engagement and road safety in the…
  • storm-in-puerto-vallarta-sweeps-vehicles-treesStorm in Puerto Vallarta Sweeps Away Vehicles and Topples Trees A sudden storm in Puerto Vallarta Sunday night swept away vehicles, downed trees and poles, and triggered patrols to clear drains—no injuries or major damage reported. A fast-moving storm struck Puerto Vallarta late Sunday night, dumping heavy rain that swept away vehicles, uprooted trees and downed utility poles across the city. Despite several reported emergencies,…
  • cancun-beaches-50-tons-sargassum-cleanupSargassum in Quintana Roo Hits 76 Beaches from Cancun to Tulum, Only 24 Clean Beaches Sargassum in Quintana Roo has reached moderate to excessive levels on 76 beaches—including Cancun—as cleanup crews race to protect tourism and coastal ecosystems. A recent survey from the Quintana Roo Sargassum Monitoring Network and the Sargassum Citizen Observatory shows 76 out of 100 beaches on the state’s Caribbean coast now face moderate to excessive seaweed…
  • real estate puerto vallartaJalisco is seizing real estate in Puerto Vallarta tied to organized crime Jalisco uses asset forfeiture to fight Puerto Vallarta money laundering by targeting properties linked to cartel funds and pursuing three major court cases. Jalisco authorities have launched a focused campaign to disrupt money laundering in Puerto Vallarta by seizing real estate tied to criminal networks. Using asset forfeiture as a legal tool, the state seeks…
  • clandestine-trash-dumping-puerto-vallartaPuerto Vallarta Removes Trash from Clandestine Dumping Sites The Directorate of Efficient Services cleared clandestine trash dumping sites in Puerto Vallarta across seven neighborhoods, urging residents to report and prevent new piles. In a targeted effort to protect public health and the environment, the Directorate of Efficient Services launched a clean-up operation across multiple neighborhoods in Puerto Vallarta this week. Teams from the…
  • couple-walks-lion-on-leash-puerto-vallartaCouple Walks Young Lion on Leash Through Puerto Vallarta Streets Where are the police? A couple was filmed walking a young lion on a leash through Puerto Vallarta, raising safety and legal questions about exotic pets and public risk. A couple caused alarm late Saturday when they led a young lion through the streets of Puerto Vallarta on a thin dog leash. The pair, speaking…
  • crocodile-killed-el-salado-estuaryCrocodile killed in El Salado estuary prompts criminal complaint The crocodile killed in El Salado estuary has led Semadet to file a criminal complaint with the FGR and Profepa, underscoring Mexico’s wildlife protection laws and plans to restart educational workshops. Authorities discovered the mutilated carcass of a roughly two-and-a-half-meter crocodile in the El Salado estuary on Friday, July 4, triggering an immediate legal response.…
Scroll to Top