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, using seaweed to disguise their approach. In Galveston Bay, Texas, certain female bottlenose dolphins and their young follow shrimp boats — swimming into the shrimp nets to take live fish and then wriggling out again, a skill requiring expertise to avoid entanglement.
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 protects them from the spines of stonefish and stingrays as they forage over shallow seabeds.
A dolphin's ability to invent novel behaviours was tested in a famous experiment by the renowned expert Karen Pryor. Two rough-toothed dolphins were rewarded whenever they came up with a new behaviour. It took just a few trials for both dolphins to realise what was required. A similar trial was set up with humans — they took about as long as the dolphins to figure out what was expected.
Dolphins are quick learners. Calves stay with their mothers for several years, allowing time for extensive learning particularly through imitation. At one dolphinarium, a person watching from the pool window noticed that when she released a puff of smoke from her cigarette, a dolphin calf immediately swam off to her mother, returned, and released a mouthful of milk, causing a similar effect to the cigarette smoke.
To keep track of relationships in a large social group, dolphins use a variety of clicks and whistles. Some species have a signature whistle — a unique sound that, like a name, allows individuals to identify each other. At the Kewalo Basin Marine Laboratory in Hawaii, Lou Herman and his team tested dolphins' ability to comprehend language using sign language. One star dolphin, Akeakamai, learned a vocabulary of more than 60 words and could understand more than 2,000 sentences. Particularly impressive was the dolphins' relaxed attitude when new sentences were introduced — the characteristic of true understanding, not rigid training.
Another test of awareness comes from mirror experiments. Diana Reiss and her researchers installed mirrors inside the New York Aquarium to test whether two bottlenose dolphins were self-aware enough to recognise their reflections. They placed non-toxic black ink markings on the dolphins' bodies. The dolphins swam to the mirror and exposed the black mark to check it out — spending more time in front of the mirror when marked than when not. The ability to recognise themselves in the mirror suggests self-awareness, a quality previously only seen in people and great apes.