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Behavior of Dolphins
– almost 40 species of dolphin
– found (31)
– usually in shallower seas
– may harass other animals
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Ok, today’s lecture is about the behavior of dolphins. Dolphins are mammals closely related to whales and porpoises. There are almost forty species of dolphin, and they vary in size from 1.2 meters and 90lb up to 9.5 meters and 10 tones. They are found worldwide (Q31) mostly in the shallower seas of the continental shelves and they are carnivores, eating mostly fish and squid.
Dolphins are highly social animals, often living in pods of up to a dozen individuals, though pod sizes and structures vary greatly between species and locations. In places with a high abundance of food, pods can merge temporarily, forming a super-pod; such groupings may exceed 1,000 (Q32) dolphins. Membership in pods is not rigid, with interchange being common.
Dolphins can, however, establish strong social bonds; they will stay with injured or ill individuals, even helping them to breathe by bringing them to the surface if needed. This altruism does not appear to be limited to their own species. A male dolphin called Moko in New Zealand was observed guiding a female Pygmy Sperm Whale together with her calf out of shallow water (Q33) where they had been stranded several times. Dolphins have also been seen protecting swimmers from sharks by swimming circles around the swimmers or charging the sharks to make them leave.
Dolphins also display culture, something long believed to be unique to humans and possibly other primate species. In May 2005, a discovery in Australia found Indo-Pacific bottlenose dolphins teaching their young to use tools (Q34). They cover their snouts with sponges to protect them while foraging for food. This knowledge is mostly transferred by mothers to daughters, unlike primates, where knowledge is generally passed on to both sexes (Q35). Using sponges as mouth protection is a learned behavior. Another learned behavior was discovered among river dolphins in Brazil, where some male dolphins use weeds and sticks as part of a sexual display.
Dolphins may also engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins engage in acts of aggression apparently for the same reasons as humans: that is disputes between companions (Q36) and competition for females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile after losing a fight. Male bottlenose dolphins have also been known to engage in infanticide, which is the killing of their young. Dolphins have also been known to kill porpoises for reasons which are not fully understood, as porpoises generally do not share the same diet as dolphins and are therefore not competitors for food supplies.
The main food of dolphins is fish and squid, and various methods of feeding exist among and within species, some apparently exclusive (Q37) to a single population. One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball. Individual members then take turns plowing through the ball, feeding on the stunned fish. Coralling is a method where dolphins chase fish into shallow water to catch them more easily. Orcas and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it, a behavior known as beach (Q38) or strand feeding. Some species also whack fish with their flukes, stunning them and sometimes knocking them out of the water. When it comes to playful behavior, dolphins show various types, often including objects, self-made bubble rings, other dolphins or other animals.
When playing with objects or small animals, common behavior 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 (Q39) from another member, or throwing it out of the water. Dolphins have also been observed harassing animals in other ways, for example by dragging birds underwater without showing any intent to eat them. Playful behavior that involves another animal species (Q40) with active participation of the other animal can also be observed, playful human interaction with dolphins being the most obvious example. However playful interactions have been observed in the wild with a number of other species as well, such as Humpback Whales and dogs.