Several kinds of territory and territorial behavior can be observed in birds around the world, allowing us to study these birds better.
A territory is an area that is defended by a bird. The word defense implies that someone will take the territory if you do not adequately defend it. Experiments with many species of birds have shown constant pressure to defend their territories. In a study, when researchers captured and removed the territory holders, new occupants of the same species quickly replaced them, usually in hours rather than days.
Social behavior in birds contrasts with territoriality, for sociality involves flocking, colonial breeding, or the common ownership or use of a particular area. However, sociality and territoriality can be combined in the same species in various ways.
Breeding pairs of crows occupy territories, while non-breeding crows live in a flock nearby, often in an unsuitable area for breeding due to a shortage of nest sites. If a territory falls vacant, it is quickly occupied by one of the flock members.
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Singing To Hold Territory
With so much pressure on territory holders, they must spend as much time as possible securing their area. However, in many situations, it is not possible for a territory holder to see all of the boundaries from one vantage point, and he cannot be on hand to see and drive away every marauder.
It would also take up too much of his time and energy if he attempted to patrol the boundary to keep out intruders. This constant vigilance is not needs as birds have another method for communicating over long distances.
Bird song has several functions, of which mate attraction is perhaps the most obvious. But in an experiment where male great tits were removed, their territories were kept free of intruders for some time by playing tape recordings of great tit songs over loudspeakers.
In other birds, the posture of the territory owner may be sufficient to signal to a potential settler that an area is already occupied. Starlings adopt a characteristic posture while singing, with the wings held slightly away from the body, the feathers of the crown and throat puffed out, and the tail directed downwards.
Starlings often adopt this posture while not singing but perched on an exposed song post within easy view of any bird looking for a territory.
At first sight, it appears strange that a bird looking for a place to settle should be deterred by a bird simply singing or displaying. When this system fails, however, and the intruder does try to stake a claim, the homeowner almost always wins the ensuing contests, whether these consist of threatening displays or physical combat.
It is not entirely clear why a male is usually victorious on his territory. It may be because of his superior knowledge of the terrain. Whatever the advantage, the presence of a bird advertising that he is the landowner is often sufficient indication to an intruder that if he does attempt to settle, he will use up valuable time and energy in a conflict that he is unlikely to win.
Types Of Territory
The kind of territory with which most people are familiar is that of the garden blackbird. In this type, a breeding pair defends a plot of land of around three acres against other blackbirds. Within this territory, the pair feed and build their nest.
Breeding pairs of robins also vigorously defend a territory in the breeding season, but unlike blackbirds, robins become aggressively territorial again in the autumn. Males and females will defend separate territories in which each individual feeds, and these autumn territories are smaller than those held by pairs in the spring.
Starlings and rooks, on the other hand, are far more social than robins and blackbirds. They stay in flocks during the breeding season, just as they flock at other times of year. It is readily apparent, from looking at a rookery, that rooks are social while nesting.
The same applies to starlings, although their requirement for holes as nest sites leads to a greater dispersal of nests and their coloniality is not aseasily seen. Sociality has its limits and around the nest both species drive off intruders.
In these species, the territory is therefore restricted to a small area around the nest. The birds are content to share their feeding grounds, and do not even defend them against birds of their own species from neighbouring colonies.
The area over which breeding rooks and starlings travel in search of food is not a defended territory, and is known as a home range. A tiny nesting territory and an even larger home range, sometimes extending 100km (60 miles) from the nest, is typical of many seabirds, such as the gannet, kittiwake and guillemot.
In the case of the guillemot, the defended area is limited to a small length of cliff ledge around the egg or chick, so that each narrow ledge looks from a distance like a line of black and white birds.
Territories with no nests In the breeding territories mentioned so far, the nest site has been a vital component. While this is the case for most British birds, there are exceptions. When shelduck return to their breeding grounds from the moulting areas to which they migrate in autumn, they spend much of the winter in flocks. In late winter, however, they form pairs. These pairs are territorial and defend feeding sites on the muddy banks of estuaries.
The ownership of a territory is, as in other species, essential for breeding: but shelduck do not breed on their territory. They breed under cover of thick vegetation, or use rabbit burrows in dunes and sea walls, some distance from the feeding territory.
During incubation, the feeding territory remains the centre of activity for the non-incubating male, and his mate leaves the nest about four times each day to feed on the territory.
In the case of ruff and black grouse, a small and vigorously defended territory is not used for nesting nor for feeding, but for display. Such display territories, or leks, are used by those males that have been able to obtain one in complex ritualised displays which become more and more intense when females are around.
The females are attracted to the display territories by the activity of the males, and visit the territories to mate. The lekking area is generally on an open piece of ground, and while 20 or more males hold territories there, the females are attracted to some males more than others. As a result, most copulations are achieved by relatively few of the males. This polygamous mating system selects the best males to father the next generation.
Like the robin in autumn, some pied wagtails occupy individual territories in winter. These are simply feeding territories, and the occupation of one of these depends both on the individual’s status and on how much food is available. Where food is predictably plentiful, highranking individual birds hold territories.
A juvenile pied wagtail may be allowed to feed within the territory, and when it does it helps in territorial defence. Where food supplies are more transient or scarce, pied wagtails feed in flocks. Should the food supply fail, as when a river bank freezes, then they vacate their plots, and join the flocks. The pied wagtail alternates between the two forms of territoriality.