11.10.2016 – Stenella
October 20, 2016
15.10.2016 – Salted herring and Sperm whale spectacle
October 23, 2016
Today we observed Pilot Whales that appeared to be sleeping. They were drifting motionless at the water surface, resembling tree logs. Dolphins and whales sleep with one side of their brain alert, and the other side of their brain asleep. This phenomenon is called ‘Unihemispheric slow-wave sleep’ (USWS). Several species groups use USWS, including cetaceans, pinnipeds, Sirenia, and several birds. For marine mammals, it allows simultaneous sleeping and surfacing to breathe. For birds, it helps them to rest during long flights. Plus, for all species using USWS, it provides the benefit that they can see any predators approaching.
Many species using USWS keep one eye open, on the opposite side of the awake hemisphere of the brain. Bird keep the eye open on the side where it is most likely that predators will approach. When many birds do this together in a flock, it’s called the ‘group edge effect’. Cetaceans also use this group edge effect, although some species use it exactly the opposite way. For example, Pacific white-sided dolphins will keep an eye open towards the group, so they can see the other animals. Researchers think this is to make sure the pod stays in cohesion, and keep social connection with the other dolphins.
by Judith Kok
Todays sightings:
Stenella:
10.00: Pilot Whales, Bottlenose Dolphins, Atlantic Spotted Dolphins
15.00: Bottlenose Dolphins, Pilot Whales
Ribeira Brava:
10.00: Pilot Whales, Bottlenose Dolphins, Atlantic Spotted Dolphins
15.00: Bottlenose Dolphins
