Territorial Behaviour in Animals

In zoology, territorial activity refers to how an animal or a group of animals defends their territory from intruders of the same species. Territorial boundaries can be marked by scents such as pheromones secreted by the skin glands of several mammals or sounds such as bird songs. If such a warning does not deter intruders, combat and chases will ensue.

Overview of Territorial Behaviour

A defence form of nest-sites, food sources, or other resources against the other members of similar species. Several animals protect areas of land from intruders, most of whom are of the same genus. Sometimes, this is accomplished by the outright aggression towards intruders, whereas, sometimes, by threat displays, by song (territorial behaviour in birds), and by scent marking (in mammals).

Territorial defence contains both benefits and costs, and animals defend territories only when it is economical to perform so. For example, spotted hyenas (Crocutes crocuta) defend territories in the Ngorongoro crater, where prey is plentiful and predictable, but not in the Serengeti plains, where prey is more seasonal. The hyenas in the Serengeti wander around a wide home range but do not defend territory. 

Several animals differ in their defence strategies depending on the food supply. When the food levels become high, intruder pressure increases, and both the squirrels (Sciuridae or the squirrel territorial behaviour) and sunbirds (Nectariniidae) give up their territories due to the defence costs becoming very great. On the other hand, foraging efficiency can plummet to the point that the animal, even with territorial protection, is unable to meet its regular energy requirements. Under these circumstances, the territory has been lost.

A few animals defend territories only during the breeding season (which is the territorial behaviour in animals). In other cases, the male territorial behaviour defends territories, known as leks, where the females come for mating. In some other cases, the territory contains vital resources, which the females need, and the males gain access to females by controlling these resources. For example, in the American bullfrog (the Rana catesbeiana), a few males achieve better mating success compared to others. These are the ones, which are able to defend a territory having the best egg-laying sites.

Adaptivity of Territorial Behaviour

Territorial activity is beneficial in a variety of ways, including allowing an animal to mate without interruption and raise its young in an environment with little competition for food. Also, it can prevent overcrowding by maintaining the optimum distance among the population members. Territories can be seasonal; in several songbirds, the mated pair defends the feeding area and nest until after the young are fledged. In communally nesting birds like gulls, the hummingbird territorial behaviour can just consist of the nest itself.

Function

The ultimate goal of animals defending and inhabiting a territory is to improve the collective or individual health of the animals displaying the action. In this biological sense, fitness relates to the ability of an animal to raise young and survive. The proximate functions of the territory defence differ. For some of the animals, the reason for such protective behaviour is to acquire and protect the food sources, mating areas, nesting sites, or to attract a mate.

Types and Size

Territories have been classified into six types among the birds.

• Type A: It is an 'all-purpose territory,' where all activities take place. For example, mating, courtship, foraging, and nesting.

• Type B: It is a nesting and mating territory, except for the majority of the foraging area.

• Type C: It is a nesting territory that includes the nest, including a small area around it. This is common in colonial water birds.

• Type D: It is a mating and pairing territory—the type of this territory defended by males in the lekking species.

• Type E: This is a roosting territory.

• Type F: Winter territory that typically includes roost sites and foraging areas. It may be equivalent (in the location) to a migratory species or for the Type A territory, maybe on the wintering grounds.

Reports of the territory size may be confused by a lack of distinction between the defended territory and home range. The shape and size of a territory can differ based on its purpose, season, the amount and quality of the resources it has, or geography. Usually, the size is a compromise of defence costs, resource needs, reproductive needs, and predation pressure.

Golden eagles (Aquila chrysaetos) have territories of up to 9,000 hectares (or 22,000 acres), least flycatchers (Epidonax minimus) have territories of up to 600 square metres (or 6,500 square feet), and gulls have territories of only a few square centimetres in the immediate vicinity of the nest.

Territories may be linear. Sanderlings (or the Calidris alba) forage on sand flats and beaches. When on the beaches, they feed either in individual territories or flocks of 10 - 120 meters of shoreline.