that dolphins are able to maintain continuous vigilance through echolocation for at least fifteen days
Dolphins are highly intelligent, social marine mammals that live in cooperative pods of up to dozen. Unlike terrestrial mammals, when dolphins sleep, they undergo unihemispheric sleep where only one side of the brain sleeps at a time and one eye remains open, meaning they can maintain awareness and control movement while asleep.
Dolphins communicate within their groups via echolocation, a mechanism by which they emit sound and listen to returning echoes to gain information about their environment. In the case of dolphins, these sounds consist of a series of clicks, which are used to find and capture prey, avoid predators and maintain group cohesion, so it ought to be available 24/7.
Now, scientists from the National Marine Mammal Foundation in San Diego, CA, USA, led by Brian Branstetter report that dolphins can remain vigilant for extended periods of time. In their study, dolphins were provided with tasks that would require the use of echolocation for a series of three five-day sessions. Two dolphins, one female aged 30 (SAY) and one male aged 26 (NAY) participated in the experiment. The dolphin's task was to continuously search the perimeter of the pen where the study took place using echolocation. Phantom targets (electronically simulated targets) were placed in different locations around the pen randomly, for the entire duration of the experiment. The dolphins were trained to press a response paddle within two minutes of detecting them.
Results showed that both dolphins were able to report the presence of phantom targets for five days with a high degree of accuracy with SAY outperforming NAY, getting 97%-99% correct. As a follow up, SAY began a 30 day testing period, which had to be cut short due to a storm at day 15. However, their results show that she had a remarkable ability throughout those 15 days to constantly echolocate and perform the task. The ability of dolphins to echolocate for at least fifteen days uninterrupted may seem extreme. However, as the researchers so eloquently put it: "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".