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Tuesday, 27-Feb-2007 08:09 Email | Share | Bookmark
Hengam Island - Dolphins - part 2

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Not Taken by me
Not Taken by me
Not Taken by me
 
 

Dolphins are aquatic mammals which are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2 m (4 ft) and 40 kg (88 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and ten tonnes (the Orca). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about ten million years ago, during the Miocene. Dolphins are considered to be amongst the most intelligent of animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture.
Origin of the name
The name is from Ancient Greek δελφίς delphis meaning "with a womb" which can be interpreted as meaning "a 'fish' with a womb"
The word is used in a few different ways. It can mean:

* Any member of the family Delphinidae (oceanic dolphins),
* Any member of the families Delphinidae and Platanistoidea (oceanic and river dolphins),
* Any member of the suborder Odontoceti (toothed whales; these include the above families and some others),
Used casually as a synonym for Bottlenose Dolphin, the most common and familiar species of dolphin.
In this article, the second definition is used. Porpoises (suborder Odontoceti, family Phocoenidae) are thus not dolphins in this sense. Orcas and some closely related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common language. A group of dolphins can be called a "school" or a "pod".

Dolphin behavior

Dolphins are often regarded as one of Earth's most intelligent species, though it is hard to say just how intelligent dolphins are as straight forward comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition. Furthermore, the difficulty and expense of doing experimental work with large aquatics means that some tests which could meaningfully be done still have not been carried out, or have been carried out with inadequate sample size and methodology. See the "cetacean intelligence" article for more details.
Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g. the spinner dolphin). Scientists are not quite certain about the purpose of this behavior, but it may be to locate schools of fish by looking at above-water signs, like feeding birds. They could also be communicating to other dolphins to join a hunt, attempting to dislodge parasites, or simply doing it for fun. Play is a very important part of dolphins' lives, and they can often be observed playing with seaweed or play-fighting with other dolphins. They even harass other locals, like seabirds and turtles. Dolphins also seem to enjoy riding waves and frequently 'surf' coastal swells and the bow waves of boats. Dolphins are also known to engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is covered with scars ranging in depth from teeth marks made by other dolphins. It is suggested that male dolphins engage in such acts of aggression for the same reasons as humans: disputes between companions or even competition for other females. Acts of agression can become so intense that targeted dolphins are known to go into exile: leave their communities as a result of losing a fight with other dolphins.
They are also willing to occasionally approach humans and playfully interact with them in the water. In return, some human cultures such as the Ancient Greeks treated them with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. There are many stories of dolphins protecting shipwrecked sailors against sharks by swimming circles around them
Dolphins are social, living in pods (also called "schools") of up to a dozen individuals. In places with a high abundance of food, pods can join temporarily, forming an aggregation called a superpod; such groupings may exceed a thousand dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. Membership in pods is not rigid; interchange is common. However, the cetaceans can establish strong bonds between each other. This leads to them staying with injured or ill individuals for support.
Because of their capacity for learning, dolphins have been employed by humans for any number of purposes. Dolphins trained to perform in front of an audience have become a favorite attraction in dolphinaria, for example SeaWorld. Such places may sometimes also provide an opportunity for humans to interact very closely with dolphins. Dolphin-human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled human children. The military has employed dolphins for various purposes from finding mines to rescuing lost or trapped humans. Such military dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that dolphins were being trained to kill Vietnamese skin divers. Reports of cooperative human-dolphin fisheries date back to Pliny. A modern human-dolphin fishery was reported in Laguna, Santa Catarina, Brazil in 1990.
In May 2005, researchers in Australia discovered a cultural aspect of dolphin behaviour: Some dolphins (Tursiops aduncus) teach their children to use tools. The dolphins break sponges off and cover their snouts with them thus protecting their snouts while foraging. This knowledge of how to use a tool is mostly transferred from mothers to daughters, unlike simian primates, where the knowledge is generally passed onto all the young, irrespective of sex. The technology to use sponges as mouth protection is not genetically inherited but a taught behaviour.
Dolphins are one of the few animals other than humans known to mate for reasons other than reproduction and especially male Bottlenose Dolphins are known to engage in sexual acts with other dolphin species, which is not always consensual, though the Bottlenose may also be submissive in such encounters.[11] Occasionally, dolphins will also show sexual behaviour towards humans.
Male dolphins have been known to engage in infanticide. Dolphins will also kill porpoises for reasons which are not fully understood, as porpoises generally do not share the same fish diet as dolphins and are therefore not competitors for food supplies

Feeding
Individual species may employ a number of methods of hunting. One such method is herding, where a superpod will control a school of fish while individual members take turns plowing through the herd, feeding. The tightly packed school of fish is commonly known as bait ball. Coralling is a method where fish are chased to shallow water where they are more easily captured. In South Carolina, coastal Bottlenose Dolphins take this one step further with what has become known as mudding, where the fish are driven onto mud banks and retrieved from there. In some places, Orcas will also come up to the beach to capture Seals. Some species also whack fish with their fluke, stunning them and sometimes sending fish clear out of the water.
2007: Year of the Dolphin
The year 2007 has been declared as (International) Year of the Dolphin by the United Nations and United Nations Environment Programme (UNEP).[16] The idea was launched by the UN's Convention on Migratory Species and the Whale and Dolphin Conservation Society (WDCS


http://en.wikipedia.org/wiki/Dolphin
http://www.yod2007.org/en/Start_page/index.html




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