海豚可连续15天不间断保持警戒状态

Dolphins sleep with only one half of their brains at a time, and according to new research published Oct. 17 in the open access journal PLOS ONE, this trait allows them to stay constantly alert for at least 15 days in a row（连续）. Brian Branstetter from the National Marine ¹ Mammal Foundation and colleagues found that dolphins can use echolocation with near-perfect accuracy continuously for up to 15 days, identifying targets and monitoring their environment. The researchers studied 2 dolphins, one male and one female, and found that they were capable of this task with no signs of fatigue ² for 5 days. The female dolphin performed additional tasks for a 15-day period. How much longer they could have continued was not studied., ,Sleeping with only one half of the brain at a time, or unihemispheric sleep, was believed to have evolved in dolphins to enable them to breathe at the surface of water even when half-asleep. This new research suggests that the need to remain vigilant³（警惕的） may also have played a role in the evolution of this sleeping behavior., ,"These majestic ⁴ beasts are true unwavering sentinels（哨兵） of the sea. The demands of ocean life on air breathing dolphins have led to incredible capabilities ⁵, one of which is the ability to continuously, perhaps indefinitely, maintain vigilant behavior through echolocation" says Branstetter.