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Animals often modify their environment to improve their chances of survival. The most common form of environmental modification is the creation of a nest. Generally, this involves occupation of a hole or cavity--a hollow twig, a hole in the ground, or a cave--which is often modified by bringing in bedding material, storing food, making escape routes, and the like. Almost as often, an animal creates a nest where nothing exists except a suitable location. Birds and squirrels that build nests in trees, rodents and insects that dig burrows, and beavers, with their complex dam and den construction exemplify this level of environmental modification.
Creation of a nest almost necessarily requires an investment of time and energy. Add to that investment any stored food, and any young residing in the nest, and you have something of high value. Almost inevitably the nest becomes the target of attacks by usurpers, predators and parasites. Selection drives the owner of the nest to defend its investment; this defense of resource is the heart of territoriality. Territoriality, of course, can extend beyond the immediate precincts of a nest to capture an animal's feeding or hunting range, but nesting and territoriality are generally tightly linked.
NestingThe architecture of nests
Nesting in aggregations
Agonism and territorial possession
Find out thy brother, wheresoe'er he is;
Territoriality is about possession. Many animal behaviorists define a territory as "any defended space", and the study of territory usually focusses on combat for possession of space. That animals would care enough about a space to fight over it implies that value is attached to the space. Usually either food or shelter confer value on a territory, and if young are in the shelter, an animal attaches additional value to the territory. In many species territorial ownership helps to attract mates, and potential mates may assess the quality a territory, rather than directly assessing the potential mate. In an extreme form of territoriality, space possession in leks is key to attracting mates, but these territories have no other value. Models for the acquisition and maintenance territory possession consider the balance between the costs of fighting for a territory and the costs of not having a territory. Two general models are useful in analyzing territorial conflicts, the hawk versus dove game, and the war of attrition model.
Willingness to fight over territorial possession is governed by a number of factors, including:
In the hawk-dove game the parties often assess one or more of these variables before determining their strategy.
Casual commentators frequently note that fights to the death are rare in territorial encounters; this is only partly true.
Sometimes, when normally territorial animals are crowded together, a dominance hierarchy forms; conflict is regulated through the hierarchy and costly injuries are avoided. However, numerous accounts of injuries during territorial conflict attest to the fact that not all animal conflict is peaceably resolved.
Territories for feeding and mating
The most common type of territorial possession is for feeding. An animal which successfully excludes others from its feeding territory insures its food supply. In this context it is important to understand the difference between an animals home range--the area in which it spends most of its time--and its territory. Home ranges are not defended or exclusively held and may overlap among individuals. Territories are defended and usually do not overlap. Feeding territories are often held by:
Feeding territories often also double as mating sites, but sometimes an animal will hold a piece of ground (or a perch) for the sole purpose of mating. When many animals hold adjacent mating territories, the entire aggregation is called a lek. In most (perhaps all) cases males are the lek-holders and females choose among those males. Although females may chose males based on their position in the lek, leks are often the site of intensive displays. Males of lek-forming species often have elaborate, sexually-selected, ornamentation which enhances their display. Leks are well-studied in:
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