Dolphins are capable of making a broad range of sounds using nasal air sacs located just below the blowhole. Roughly three categories of sounds can be identified: frequency modulated whistles, burst-pulsed sounds, and clicks. They communicate with whistle-like sounds produced by vibrating connective tissue, similar to the way human vocal cords function, and through burst-pulsed sounds, though the nature and extent of that ability is not known. The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals.
Bottlenose dolphins have been found to have signature whistles, a whistle that is unique to a specific individual. These whistles are used in order for dolphins to communicate with one another by identifying an individual. It can be seen as the dolphin equivalent of a name for humans. In order to obtain each individual whistle sound, dolphins undergo vocal production learning. Bottlenose dolphins have a strong memory when it comes to these signature whistles, and have been known to relate to the signature whistle of an individual they have not encountered for over twenty years.
Dolphins show various types of playful behaviour, often including objects, self-made bubble rings, other dolphins, or other animals. When playing with objects or small animals, common behaviour includes carrying the object or animal along using various parts of the body, passing it along to other members of the group or taking it from another member, or throwing it out of the water.
Dolphins in captivity can copy what humans do. This is an amazing mental ability, and its pinnacle is illustrated by the famous story of Dolly, a calf in an aquarium in South Africa. Looking out through the viewing window, Dolly saw a man exhale cigarette smoke. She swam to her mother, suckled, then came back to the window and released the milk into a cloud around her head.
Dolphins have also been observed harassing animals, for example by dragging birds underwater without showing any intent to eat them. Playful behaviour that involves another animal species with active participation of the other animal has also been observed. Playful dolphin interactions with humans are the most obvious examples, followed by those with humpback whales and dogs.
Juvenile dolphins off the coast of Western Australia have been observed chasing, capturing, and chewing on blowfish. While some reports state that the dolphins are becoming intoxicated by the tetrodotoxin in the fish’s skin, others say that dolphins are merely playing with the blowfish as they often do with other fish.
If you see a dolphin with one eye closed, and moving slowly or not at all, it is probably asleep. But only one half of their brain sleeps at a time, so the other eye will be open. And a mother always sleeps with the eye open that faces towards her calf! Even crazier, when the sleeping half of the brain wakes up, it knows what the waking half experienced on its watch!
The Indus river dolphin has a sleep method that is different from that of other dolphin species. Living in water with strong currents and potentially dangerous floating debris, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds.
You can find more interesting facts about dolphins in the book titled “A Book about Dolphins” which I used for this story series.
The authors, David and Lesley, put their hearts and souls into this amazing book. They have worked for more than a decade with wild dolphins in the Port Stephens-Great Lakes Marine Park. Only their love and passion exceed their knowledge about these majestic animals.