To see what’s above them. From here:
Dolphins have limited flexibility in their neck, and are unable to see above them – their eyes are oriented so that they can only look forwards, sideways and down. When a fish is swimming above them, the dolphin simply turns upside down to be able to see the fish. Inverted hunting enables dolphins to catch prey that is sitting very close to the surface of the water
You learn something every day. It never occurred to me that dolphin vision might be restricted like that. This was a while ago, so I can’t remember if there was any pattern to how the dolphins were swimming around the tank which might have indicated if they were food hunting, or possibly just monitoring their surroundings.
I’ve been stood on a a beach and watched dolphins bodysurf.
“You call that a good long ride? Hold my beer and watch this.”
It all seems like innocent fun until someone gets beached.
(Note: kidding aside, Ivreally have seen small dolphins playing in the waves.)
It’s a dolphin gang ritual.
If you think that’s bad, the killer whale gangs are tipping boats.