In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics (and, occasionally, animals of other species). Animals that defend territories in this way are referred to as territorial.
Territorial animals defend areas that contain a nest, den or mating site and sufficient food resources for themselves and their young. Defense rarely takes the form of overt fights: more usually there is a highly noticeable display, which may be visual (as in the red breast of the robin), auditory (as in much bird song, or the calls of gibbons) or olfactory, through the deposit of scent marks. Many territorial mammals use scent-marking to signal the boundaries of their territories; the marks may be deposited by urination, by defecation, or by rubbing parts of the bodies that bear specialised scent glands against the substrate. For example, dogs and other canids scent-mark by urination and defecation, while cats scent-mark by rubbing their faces and flanks against objects, as well as by the notoriously persistently smelly spraying of urine by tomcats. Many prosimians use territorial marking; for example, the Red-bellied Lemur creates territories for groups of two to ten individuals in the rainforests of eastern Madagascar by scent marking: the male Diademed Sifaka also scent marks defended territories in some of these same rainforests. Humans build physical impediments and visual warnings to mark defended territories. The male Western fence lizard defends a territory by posturing and combat, but less intensely after the mating season.
Spraying (also known as territorial marking) is behavior used by animals to identify their territory. Most commonly, this is scent marking, accomplished by depositing strong-smelling substances such as urine at prominent locations within the territory. Often the scent contains carrier proteins, such as the major urinary proteins, to stabilize the odors and maintain them for longer.
Not only does the marking communicate to others of the same species, but it is also noted by prey species and avoided. For example felids such as leopards and jaguars mark by rubbing themselves against vegetation. Some prosimians, such as the Red-bellied Lemur, also use scent marking to establish a territory. Many ungulates, for example the Blue Wildebeest, use scent marking from two glands, the preorbital gland and a scent gland in the hoof.
Territories may be held by an individual, a mated pair, or a group. Territoriality is not a fixed property of a species: for example, robins defend territories as pairs during the breeding season and as individuals during the winter, while some nectarivores defend territories only during the mornings (when plants are richest in nectar). In species that do not form pair bonds, male and female territories are often independent, in the sense that males defend territories only against other males, and females only against other females; in this case, if the species is polygynous, one male territory will probably contain several female territories, while in some polyandrous species such as the Northern Jacana, this situation is reversed.
Quite often territories that only yield a single resource are defended. For example, European Blackbirds may defend feeding territories that are distant from their nest sites, and in some species that form leks, for example the Uganda kob (a grazing antelope), males defend the lek site (which is used only for mating).
Territoriality is only shown by a minority of species. More commonly, an individual or a group of animals will have an area that it habitually uses but does not necessarily defend; this is called its home range. The home ranges of different groups often overlap, and in the overlap areas the groups will tend to avoid each other rather than seeking to expel each other. Within the home range there may be a core area that no other individual group uses, but again this is as a result of avoidance rather than defense.
Behavioural ecologists have argued that food distribution determines whether a species will be territorial or not. This however, though true as far as it goes, is too narrow a point of view. As mentioned above, there are several kinds of territoriality; for example, the defence of lek areas by kob has nothing to do with food. Many other examples of territorial defence, including fish, birds or even invertebrates, are related to competition for mates or safe lairs, rather than food. Territoriality will emerge where there is a focused resource that provides enough for the individual or group, within a boundary that is small enough to be defended without the expenditure of too much effort.
Many birds, particularly seabirds, though they nest in dense communities, are nonetheless territorial in that they defend their nesting site to within the distance that they can reach while brooding. This is necessary to prevent attacks on their own chicks or nesting material from neighbours. Commonly the resulting superimposition of the short-range repulsion onto the long-range attraction characteristically leads to the well-known roughly hexagonal spacing of nests. Interestingly, one gets a similar hexagonal spacing resulting from the territorial behaviour of gardening limpets such as species of Scutellastra. They vigorously defend their gardens of particular species of algae, that extend for perhaps 1–2 cm around the periphery of their shells.
Territoriality is least likely with insectivorous birds, where the food supply is plentiful but unpredictably distributed. Swifts rarely defend an area larger than the nest. Conversely, other insectivorous birds that occupy more constrained territories, such as the ground-nesting Blacksmith Lapwing may be very territorial, especially in the breeding season, where they not only threaten or attack many kinds of intruders, but have stereotyped display behaviour to deter conspecifics sharing neighbouring nesting spots.
Conversely, large solitary (or paired) carnivores, such as bears and the bigger raptors require an extensive protected area to guarantee their food supply. This territoriality will only break down when there is a glut of food, for example when Grizzly Bears are attracted to migrating salmon.