Animals Defend Their Territory

Quite ten 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 species. More commonly, an individual or a group animals will have an area that it habitually uses but does not necessarily defend; this is called its home range. The home ranges different groups ten 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 avoidance rather than defense.
Behavioural ecologists have argued that food distribution determines whether a species will be territorial or not. 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 too much effort.
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.