The trait is called unihemispheric sleep, and allows dolphins to remain vigilant at any time and be able to breathe at the surface of water when needed, even during sleep. Researchers in the US wanted to test how long can a dolphin stay alert without interruption. The result: Up to 15 days, maybe even more.
The study, published in the open access journal PLOS ONE, shows how two dolphins, one female and one male, were able to correctly detect and report targets even when sleeping. In the case of the male, the researchers tested its capacities for 5 days; in the female, which showed an overall better performance, they extended the period to 15 days, resulting in “near perfect performance with no significant decrement over time,” as reported in the paper.
“These majestic beasts are true unwavering sentinels of the sea,” said co-author Brian K. Branstetter, from National Marine Mammal Foundation in San Diego, California. “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 behavior through echolocation.”
Brian K. Branstetter, James J. Finneran, Elizabeth A. Fletcher, Brian C. Weisman, & Sam H. Ridgway (2012). Dolphins Can Maintain Vigilant Behavior through Echolocation for 15 Days without Interruption or Cognitive Impairment PLOS ONE : 10.1371/journal.pone.0047478