In zoology, the actions by which an animal, or group of animals, protects its territory from incursions by others of its species. Territorial boundaries may be marked by sounds (e.g., birdsong), scents, or even piles of dung. If such advertisement does not discourage intruders, chases and fighting follow. Territories may be seasonal (usually for nesting and feeding the young) or maintained permanently (for hunting and living). Territorial behaviour benefits the species by permitting mating and rearing young without interruption and by preventing overcrowding and minimizing competition for food.

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In animals, any activity directed toward perpetuation of a species. Sexual reproduction, the most common mode, occurs when a female's egg is fertilized by a male's sperm. The resulting unique combination of genes produces genetic variety that contributes to a species' adaptability. The stages of approach, identification, and copulation are well developed to avoid predators and the wastage of eggs and sperm. Most one-celled and some more-complex organisms reproduce asexually. Seealso courtship behaviour.

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Involuntary response by an animal, resulting in a predictable and relatively fixed behaviour pattern. Instinctive behaviour is an inherited mechanism that serves to promote the survival of an animal or species. It is most apparent in fighting and sexual activity. The simplest form is the reflex. All animals have instinct, but, in general, the higher the animal form, the more flexible the behaviour. Among mammals, learned behaviour often prevails over instinctive behaviour.

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Any action of an animal directed toward obtaining nutrients. Each species evolves methods of searching for, obtaining, and ingesting food for which it can successfully compete. Some species eat only one type of food, others a variety. Among invertebrates food choices are instinctual, while among vertebrates they are learned.

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Type of activity, exhibited by animals exposed to adverse stimuli, in which the tendency to flee or to act defensively is stronger than the tendency to attack. Vision is the sense that most often produces avoidance behaviour (e.g., small birds react to the sight of an owl), but sound (e.g., a warning cry) may do so as well.

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Ritualized activity by which an animal conveys specific information. The best-known displays are visual, but others rely on sound, smell, or touch. Agonistic (aggressive) displays make it unnecessary to chase intruders from a territory or for animals to injure each other in competition for mates. One type of defensive display deceives predators or lures them away from vulnerable young. Seealso birdsong; courtship behaviour.

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Animal activity that results in mating and reproduction. Courtship may simply involve a few chemical, visual, or auditory stimuli, or it may be a highly complex series of acts by two or more individuals using several modes of communication. Females of some insect species use pheromones to attract males from a distance. Painted turtles court by touch, and the courtship songs of frogs are heard on spring nights across much of the world. Certain bird species have complex courtship patterns. Courtship is important as an isolating mechanism to prevent different species from interbreeding, and elaborate courtship rituals help strengthen pair bonds that may last through the raising of the young or longer. Seealso display behaviour.

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Behaviour in a complex system that appears irregular or unpredictable but is actually determinate. The apparently random or unpredictable behaviour in systems governed by complicated (nonlinear) deterministic laws is the result of high sensitivity to initial conditions. For example, Edward Lorenz discovered that a simple model of heat convection exhibits chaotic behaviour. In a now-classic example of such sensitivity to initial conditions, he suggested that the mere flapping of a butterfly's wings could eventually result in large-scale changes in the weather (the “butterfly effect”).

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or behaviour modification

Application of experimentally derived principles of learning to the treatment of psychological disorders and the control of behaviour. The concept, which has its roots in the work of Edward L. Thorndike, was popularized in the U.S. by theorists of behaviourism, including B.F. Skinner. Behaviour-therapy techniques are based on the principle of operant conditioning, in which desired behaviours are rewarded. There is little or no concern for conscious experience or unconscious processes. Such techniques have been applied with some success to disturbances such as enuresis, tics, phobias, stuttering, obsessive-compulsive disorder, and various neuroses. Behaviour modification more generally refers to the application of reinforcement techniques for shaping individual behaviour toward some desired end or for controlling behaviour in classrooms or institutional situations. Seealso psychotherapy.

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The study of the interaction of heredity and environment insofar as they affect behaviour. The question of the determinants of behaviour, commonly called the “nature-nurture” controversy, was initially investigated by English scientist Sir Francis Galton. A balanced view that recognized the importance of both genetics and environment prevailed in the 1970s. Modern research is focused on identifying genes that affect behavioral dimensions, such as personality and intelligence, and disorders, such as depression and hyperactivity. Two quasi-experimental methods of study, the twin method and the adoption method, are used to quantify the genetic and environmental contributions to an individual's behaviour.

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Any action of an animal intended to injure an opponent or prey animal or to cause an opponent to retreat. Aggression may be caused by various stimuli. Within its own group, an animal must display aggressive postures to maintain its position within the hierarchy (e.g., the pecking order of chickens). A threat by itself, as in ruffled feathers or teeth revealed in a snarl, is usually sufficient to maintain an already-established social order. Aggression often occurs just before mating season, when males win their choice of females and territories.

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In animal behaviour, a gens (pl. gentes) is a race of host-specific brood parasite. Brood parasites, such as cuckoos, which use multiple host species to raise their chicks, evolve different gentes, each one specific to its host species. This specialisation allows the parasites to lay eggs that mimic those of their hosts, which in turn reduces the chances of the eggs being rejected by the hosts.

The exact mechanisms of the evolution and maintenance of gens is still a matter of some research, however, it is believed that in cuckoos, gens-specific properties are sex-linked and lie on the W chromosome of the female. Male cuckoos, which have no W chromosome, are able to mate with females of any gens, and thereby maintain the cuckoo as one species.

References

• Gibbs et al. (2000), Genetic evidence for female host-specific races of the common cuckoo, Nature 407, 183-186
• Davies, N. (2000) Cuckoos, Cowbirds and other Cheats. T. & A. D. Poyser: London ISBN 0-85661-135-2
• Dawkins, R. (1982) The Extended Phenotype. Oxford University Press: Oxford ISBN 0-19-288051-9