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Tools are used by some animals to perform behaviours including the acquisition of food and water, grooming, defence, recreation or construction. Originally thought to be a skill only possessed by humans, some tool use requires a sophisticated level of cognition. There is considerable discussion about the definition of what constitutes a tool and therefore which behaviours can be considered as true examples of tool use. A wide range of animals are considered to use tools including mammals, birds, fish, cephalopods and insects. Rarely, animals have been observed making their own tools, e.g. primates sharpening a stick to use as a weapon,〔 or removing leaves and twigs from a branch and fishing for termites with a stem frayed by chewing. ==Definitions and terminology== The key to identifying tool use is defining what constitutes a tool. Researchers of animal behavior have arrived at different formulations. In 1980, Beck published a widely used definition of tool use.〔Beck, B., (1980). ''Animal Tool Behaviour: The Use and Manufacture of Tools by Animals'' Garland STPM Pub.〕 More recently, this has been modified to - Other, briefer definitions have been proposed - Others, for example Lawick-Goodall,〔Lawick-Goodall, J.V., (1970). Tool using in primates and other vertebrates in Lehrman, D.S, Hinde, R.A. and Shaw, E. (Eds) ''Advances in the Study of Behaviour, Vol. 3.'' Academic Press.〕 distinguish between "tool use" and "object use". Different terms have been given to the tool according to whether the tool is altered by the animal. If the "tool" is not held or manipulated by the animal in any way, such as an immobile anvil, objects in a bowerbird's bower, or a bird using bread as bait to catch fish,〔(【引用サイトリンク】title=Video of a bird apparently using bread as bait to catch fish )〕 it is sometimes referred to as a "proto-tool". Several studies in primates and birds have found that tool use is correlated with an enlargement of the brain as a whole or of particular regions. For example, true tool-using birds have relatively larger brains than proto-tool users.〔 When an animal uses a tool that acts on another tool, this has been termed use of a "meta-tool". For example, New Caledonian crows will spontaneously use a short tool to obtain an otherwise inaccessible longer tool that then allows them to extract food from a hole.〔 Similarly, bearded capuchin monkeys will use smaller stones to loosen bigger quartz pebbles embedded in conglomerate rock, which they subsequently use as tools.〔 Rarely, animals may use one tool followed by another, for example, bearded capuchins use stones and sticks, or two stones.〔 This is called "associative", "secondary" or "sequential" tool use. Some animals use other individuals in a way which could be interpreted as tool use, for example, ants crossing water over a bridge of other ants, or weaver ants using conspecifics to glue leaves together. These have been termed "social tools".〔Pierce, J.D., (1986). A review of tool use in insects. The Florida Entomologist, 69: 95-104〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tool use by animals」の詳細全文を読む スポンサード リンク
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