Intelligence

"Intelligence" is a term with many definitions and interpretations. It's difficult enough to measure in humans let alone other animals. Large brains are traditionally associated with greater intelligence, and the brain of the adult bottlenose dolphin is about 25% heavier than the average adult human brain. Generally though, larger mammals tend to have larger brains, and so a more accurate estimate of brain power comes from the ratio of brain size to body size - the "encephalisation quotient" (EQ). While river dolphins have an EQ of 1.5, some dolphins have EQs that are more than double those of our closest relatives: gorillas have 1.76, chimpanzees 2.48, bottlenose dolphins 5.6. The bottlenose's EQ is surpassed only by a human's, which measures 7.4 (Australopithecines - hominids that lived around 4m years ago - fall within the dolphin range: 3.25-4.72). But we don't know enough about the workings of the brain to be sure of what these anatomical measurements truly represent. Today, most scientists share the view that it is behaviour, not structure, that must be the measure of intelligence within a species.
Dolphins have invented a range of feeding strategies that more than match the diversity of habitats in which they live. In an estuary off the coast of Brazil, tucuxi dolphins are regularly seen capturing fish by "tail whacking". They flick a fish up to 9 metres with their tail flukes and then pick the stunned prey from the water surface. Peale's dolphins in the Straits of Magellan off Patagonia forage in kelp beds, use the seaweed to disguise their approach and cut off the fishes' escape route.
Dolphins can also use tools to solve problems. Scientists have observed a dolphin coaxing a reluctant moray eel out of its crevice by killing a scorpion fish and using its spiny body to poke at the eel. Off the western coast of Australia, bottlenose dolphins place sponges over their snouts, which protect them from the spines of stonefish and stingrays as they forage over...