Cetaceans - whales and dolphins - are among the brainiest of beings.
In terms of sheer brain size, the sperm whale is top on Earth, with a brain six times larger than that of a human being.
Now, scientists have identified key differences among cetaceans linked to brain size.
A study of 90 cetacean species found that those with larger brains exhibit greater complexity in social structures as well as behaviours, with species like the killer whale and sperm whale leading the way.
Dolphin and whale societies are at least as complex as what we have observed in primates.
They are extremely playful, they learn from each other, have complex communication.
One problem for understanding just how smart they are is how difficult it is to observe them and to understand their marine world.
Therefore, we have only a glimpse of what they are capable of.
The researchers created a comprehensive database of brain size, social structures and cultural behaviours across cetacean species.
The group of species with the largest brain size relative to body size was the large whale-like dolphins such as the killer whale, the similar-looking false killer whale and the pilot whale.
Killer whales have cultural food preferences, have matriarchs that lead and teach other group members, and cooperatively hunt.
In terms of intra-species food preferences, certain killer whale populations, also known as orcas, prefer salmon whereas others prefer seals or other whales or sharks depending on their group’s culture.
Other big-brained cetaceans also demonstrate sophisticated behaviours.
Mother sperm whales organise babysitting duties using other members of their pod to protect their young while they hunt for food down deep.
The distinctive vocalisations sperm whales use to communicate sometimes differ depending upon where they live, much like regional dialects in human language.
