Territoriality: A lot of birds try to keep other birds out of all or part of their home range, which is the area they typically occupy for their daily activities. When they do, we say they are defending a “territory. “This behavior is typically directed toward other members of the same species and takes place during the breeding season.” Most of the time, territoriality seems to be an attempt to control resources, particularly food supplies or mate availability. However, territoriality could also function as a defense mechanism against predators. Some birds defend their entire home range. Others just protect their food sources, mating grounds, or nest sites. Certain tropical hummingbirds drive other nectar-feeding birds, including some butterflies, and the majority of other hummingbirds away from their preferred nectar-bearing flower patches. Some sandpipers, grouse, and other birds defend small areas on their leks, which are patches of ground used for communal mating displays. The majority of seabirds that nest in colonies only protect the area around their nests, probably to safeguard their eggs and, in the case of certain penguins, the pebbles used to build their nests. Territoriality keeps certain species of camouflaged birds from occurring in flocks or clusters during breeding by distributing them and their nests fairly evenly throughout their habitat. This could therefore lessen the risk of predation because many predators will focus on a particular type of prey once one or a small number of that prey type are found (the predator creates a “search”). Clustering can lessen the security of each individual prey by encouraging predators to form a search (though non-cryptic birds may benefit from clustering). Animals have developed “keep-out” signals to ward off potential invaders in order to reduce the necessity for actual physical contact when defending territories. Of course, the most noticeable sounds in birds are the males’ songs. It has long been believed that bird songs are lovely melodies meant to enhance human surroundings, but in reality, they serve primarily as declarations of territory and warnings of potential violent defense. Naturally, the territory owner will frequently step up its actions to include visual displays, chases, and even combat if the auditory warning is ineffective. Usually highly stereotyped, this territorial behavior can be experimentally elicited by playing recorded songs or by using stuffed taxidermy mounts. The extent of a person’s territory varies greatly between species and even within species. The territories of golden eagles are roughly 35 square miles, those of least flycatchers are roughly 700 square yards, and those of sea gulls are only a few square feet in the immediate area of the nest. Within the same species, territory size frequently varies from habitat to habitat. Song Sparrows inhabit shrublands in relatively resource-poor Ohio, with territories spanning several thousand square yards. In the abundant salt marshes of the San Francisco Baylands, their size is roughly one-fifth to tenth that of other places. To ensure a sufficient supply of food, the San Francisco birds need to defend a significantly smaller area. SEE: Interspecific Territoriality; Population Dynamics; Vocal Dialects; Vocal Functions. Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.
Thus far, our discussion has focused on intraspecific territoriality within the same species, which is the most prevalent Nonetheless, there is also some interspecific competition among various species. Birds of a particular species typically allow other birds to inhabit their territories and will only chase out conspecifics. A Bald Eagle and a Great Horned Owl, e. g. nested just one meter apart in the same Florida tree. Swallows often nest in eagle and hawk nests. When other birds pose a threat as competitors or predators, they frequently drive them from their territories. Oystercatchers, e. g. will chase gulls, ravens, and crows from their territories.
Territoriality can have a significant impact on populations, forcing some individuals into less-than-ideal environments where they are unable to reproduce. Territoriality may therefore result in a lower success rate for hatching or fledging, or a rise in adult and/or juvenile mortality. A study conducted in Finland on the Willow Warbler, a species that prefers spruce-birch forests, revealed that nearly all pairs of breeding warblers were located in these forests during years when the species’ abundance was low. The warblers were found in other habitats during periods of high abundance, but their densest population was in spruce-birch forests. Therefore, in high-abundance years, population densities are significantly higher in suboptimal habitats. Years of high abundance saw a slight increase in the number of territories and a slight decrease in their sizes, allowing more to fit in the best habitats. So territoriality forced birds into suboptimal but adequate habitats.
Researchers observed the growth of Pied Flycatcher nestlings and discovered that while both high and low density breeding populations performed well in favorable conditions, the low density populations fared better in adverse weather and/or food scarcity. Food supply and territory size were found to be directly correlated by Stenger (1958); the more food available, the smaller the territory and the more there were Therefore, the availability of resources and the size of the population typically dictate the territory’s size. But there are lots of modifications to this general rule.
Territories obviously affect the social system of birds. The female Fiery-throated Hummingbird of Costa Rica and Panama is drawn to the flowers in its territory, but she feeds on different flowers than the male. The male owns a territory. The female chooses the territories based more on the best source of food than the male’s physical attractiveness. Therefore, selection favors the most aggressive male through evolution.
Because defending a territory requires energy and the territory contains scarce resources, territorial integrity is maintained. Brown created a territoriality model in 1964 that states that competition for resources increases with population size and occurs when resources are scarce. Furthermore, the effect of population size increases with the amount of resources required. To get the resources in the face of intense competition, one must be extremely aggressive. However, if economic defensibility is too expensive, then territories are not held.