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A herd is a social grouping of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is referred to as ''herding''. The term ''herd'' is generally applied to mammals, and most particularly to the grazing ungulates that classically display this behaviour. Different terms are used for similar groupings in other species; in the case of birds, for example, the word is ''flocking'', but ''flock'' may also be used, in certain instances, for mammals, particularly sheep or goats. A group of quail is often referred to as a covey. Large groups of carnivores are usually called ''packs'', and in nature a herd is classically subject to predation from pack hunters. Special collective nouns may be used for particular taxa (for example a flock of geese, if not in flight, is sometimes called a ''gaggle'') but for theoretical discussions of behavioural ecology, the generic term ''herd'' can be used for all such kinds of assemblage. The word ''herd'', as a noun, can also refer to one who controls, possesses and has care for such groups of animals when they are domesticated. Examples of herds in this sense include shepherds (who tend to sheep), goatherds (who tend to goats), cowherds (who tend cattle), and others. ==Reasons for animals to form a herd== When an association of animals (or, by extension, people) is described as a herd, the implication is that the group tends to act together (for example, all moving in the same direction at a given time), but that this does not occur as a result of planning or coordination. Rather, each individual is choosing behaviour that corresponds to that of the majority of other members, possibly through imitation or possibly because all are responding to the same external circumstances. A herd can be contrasted with a coordinated group where individuals have distinct roles. Many human groupings, such as army detachments or sports teams, show such coordination and differentiation of roles, but so do some animal groupings such as those of eusocial insects, which are coordinated through pheromones and other forms of animal communication. The question of why animals group together is one of the most fundamental in sociobiology and behavioural ecology. As noted above, the term herd is most commonly used of grazing animals such as ungulates, and in these cases it is believed that the strongest selective pressure leading to herding rather than a solitary existence is protection against predators. There is clearly a tradeoff involved, since on the one hand a predator may hesitate to attack a large group of animals, while on the other a large group offers an easily detected target. In the case of predators, it is often unclear whether the term herd is appropriate, since there may be some degree of coordination or role differentiation in group hunting. Predator groups are commonly smaller than grazing groups, since although a pack may be more effective at pulling down prey than a single animal, the prey then has to be shared between all members, so that the weaker animals will often be better off hunting smaller prey on their own. 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「herd」の詳細全文を読む スポンサード リンク
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