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Avian Social Interactions: Territoriality and Flocking. WILD 4060/6060 Field Ornithology. Territory and Home Range. Territory – any fixed area defended continuously for some period of time. Home range – an area used by an animal in the course of its normal daily activities.
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Avian Social Interactions:Territoriality and Flocking WILD 4060/6060 Field Ornithology
Territory and Home Range Territory – any fixed area defended continuously for some period of time. Home range – an area used by an animal in the course of its normal daily activities. Considered roughly the same thing for birds. Territories are usually established for the purpose of defending a limited resource. Also, for breeding territories, a nest and mate are usually contained within the territory, and will be vigorously defended. The result is that the population size is regulated and resources are not over-consumed.
Types of Territories Oropendola nests Most songbirds (and their allies; e.g. cuckoos, hummingbirds, etc.), woodpeckers, raptors, and kingfishers, have an all-purpose territory, in which they find all their food, build a nest and raise young. Many waterbirds, especially colonial nesters, defend a small area around the nest, but will tolerate other individuals near them when they feed away from the colony, and often form flocks. Even in flocks, though, each bird will defend a small area around itself. Other oddities exist.
Territory-size Regulation in Black-shouldered Kites (Elanuscaeruleus)* BSKI occupy coastal grassland in northern California, where they feed almost entirely on Microtuscalifornicus. M. californicusexhibit a 12-month population cycle, in which their density fluctuates from only a few to about 1000/ha. Other raptors, including BSKI, migrated there in fall, left in spring Dunk (1991) measured BSKI territory sizes year-round Found that territory size was related to both food and # of competitors – proximate versus ultimate factors. * Now known as White-tailed Kite
Key players in the Arcata grassland ecosystem Intraspecific encounters were often violent Keystone prey item – California vole (Microtuscalifornicus) Kite’s exact position could be measured when they perched or hovered Even wading birds ate voles And so were interspecific encounters
Summary of findings Kite territory size ranged from 1.6 to 21.5 ha (n=26) Despite this, mean #voles/territory was remarkably constant (~1500, std.err. =163) year round Competitor (all diurnal raptors) abundance ranged from 4.8 to 31.0 individuals per km2 and was strongly correlated with vole abundance. Territory size inversely correlated with both food abundance and #competitors, but more strongly with the latter So the immediate (proximate) factor the kites responded to was the # of competitors around them, but food was the ultimate influence on the # of raptors, and ultimately controlled territory size.
The inverse relationship between food abundance and territory size in known as the Food Value Theory (Stenger 1958). • Does it hold for the majority of species that obtain food in a 3-dimensional area? • Yes: Marshall and Cooper showed that • Red-eyed Vireos’ territory volume was • inversely related to caterpillar density. • Also holds for fish. • Does it hold for migratory species, which must assess a territory’s future food value when they arrive in the spring? • Yes: Ovenbirds have been shown to • use structural cues (litter depth) to • assess habitat and adjust territories. • Also holds for REVI, whose territories • were inversely related to foliage • density. • Known as Structural Cues Hypothesis From Marshall and Cooper (2004). Ecology.
