Other Comments Strandings are not common among this species. This is perhaps because many herds remain mostly further out to sea. Common dolphins do not sleep with both eyes closed. The dolphin closes one eye for 5 to 10 minutes and then the other eye. In a 24 hour period each separate eye is closed for an average of 3 to 4 hours.
Common dolphins are mammals.
Therefore, unlike fish they cannot breathe underwater via gills. Dolphins have a blowhole on top of their heads and to breathe they must jump out of the water. They surface several times a minute to breathe. Lastly, dolphins are intelligent organisms. Their intelligence lies somewhere between that of dogs and chimpanzees.