It sounds like a hoax. If brains could be smaller, then heads could be smaller, and there ought to be some evolutionary pressure for that, in humans, at least: giving birth is not easy.
I don't know about other animals. There is particularly strong evolutionary pressure for birds that fly to have efficient brains (cognition / mass). Perhaps whales don't care so much if their brains are inefficiently large.
I don't know about other animals. There is particularly strong evolutionary pressure for birds that fly to have efficient brains (cognition / mass). Perhaps whales don't care so much if their brains are inefficiently large.