Flock (birds)

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Red-billed queleas form enormous flocks--sometimes tens of thousands strong. Flock of Birds (7175071318).jpg
Red-billed queleas form enormous flockssometimes tens of thousands strong.
Starlings flocking, a predator bird can be seen upper right Starling flock with nearby predator.jpg
Starlings flocking, a predator bird can be seen upper right

A flock is a gathering of individual birds to forage or travel collectively. [1] Avian flocks are typically associated with migration. Flocking also offers foraging benefits and protection from predators, although flocking can have costs for individual members. [2]

Contents

Flocks are often defined as groups consisting of individuals from the same species. However, mixed flocks consisting of two or more species are also common. Avian species that tend to flock together are typically similar in taxonomy and share morphological characteristics such as size and shape. [3] Mixed flocks offer increased protection against predators, which is particularly important in closed habitats such as forests where early warning calls play a vital importance in the early recognition of danger. The result is the formation of many mixed-species feeding flocks. [4]

Mixed flocks

While mixed flocks are typically thought to be composed of two different species, it is specifically the two different behaviours of the species that compose a mixed flock. Within a mixed flock there can be two different behavioural characteristics: sally and gleaner. Sallies are individuals that act as guards of the flock and consume prey in the air during flight. On the other hand, gleaners are those that consume prey living within vegetation. [5]

Studies have shown that as resources in the aerial environment increase, the flock will possess more sallies than gleaners. [5] This has been shown to occur during forest fires in which insects have been flushed from vegetation, however this can also be done by the gleaners. [5] When gleaners obtain meals from vegetation it causes the other prey within the vegetation to be flushed out into the aerial environment. [5] It is through this specific behaviour of feeding among vegetation that the gleaners indirectly increase the foraging rate of the sallies. [5]

Those birds that are more rare and therefore less abundant in an environment are more likely to perform in this mixed flock behaviour. [2] Despite the fact that this bird is more likely to be a subordinate, its ability to obtain food increases substantially. [2] As well this bird is now less likely to be attacked by a predator because predators have a lower success rate when attacking large flocks. [2]

Safety from predation

Ground squirrels in an erect position upon hearing the predation alarm call from conspecifics Xerus inauris.jpg
Ground squirrels in an erect position upon hearing the predation alarm call from conspecifics

The ability to avoid predation is one of the most important skills necessary in order to increase one's fitness. It can be seen that by ground squirrels living in colonies, the ability to recognize a predator is rapid. [6] The squirrel is then able to use vocalizations to warn conspecifics of the possible threat. [6] This simple example demonstrates that flocks are not only seen in bird species or a herd of sheep, but it is also apparent in other animals such as rodents. This alarm call of the ground squirrel requires the ability of the animal to first recognize that there is danger present and then to react. This type of behaviour is also seen in some birds. [2] It is important to note that by making an alarm call to signal members of the flock one is providing the predator with an acoustical cue to the location of a possible prey. [2] The benefit here is if the members of the flock are genetically related to one another. [2] If this is true, even if the bird that signalled the flock were to die its fitness would not decrease according to Hamilton's Rule. [2] However another study involving thick-knees challenged whether or not an animal had to recognize the presence of a predator for protection against it.

Aggressive display between two black-headed gulls Taistelevat lokit E.jpg
Aggressive display between two black-headed gulls

Thick-knees are birds that are seen in large flocks during particular seasons in various regions of the world. [7] During the nonbreeding season, Peruvian thick-knees in Chile are reported to have an average of 22.5 birds — a mixture of adults and youngsters — in their flocks. [7] Young birds were observed learning anti-predator behaviour strategies from adults during this time. [7] Researchers believe that the flocking behaviour may help to decrease a predator's success rate when attacking the flock, rather than increasing the ability of the flock to spot an approaching predator. [7]

By birds co-existing with one another in a flock, less time and energy is spent searching for predators. [2] This mutual protection of one another within the flock is one of the benefits to living within a group. [2] However, as flock numbers increase the more aggressive individuals within the flock become towards one another. [2] This is one of the costs to living within a flock. [2] It is often seen that flocks are dynamic and thus fluctuate in size depending on the needs of individuals in order the maximize benefits without incurring a large amount of costs. [2]

By living in a large flock, birds are also able to attack the predator with a stronger force compared to if the bird was on its own. In the black-capped chickadees it can be seen that flocks of birds can produce a mobbing call when it visualizes a possible predator. [8] In response the black-capped chickadees within the flock surround the predator and attack it in a mob-like fashion in order to force the predator to leave. [2] This is known as mobbing. [2] This mobbing behaviour is quickly learned by the juveniles within a flock meaning that these individuals will be better equipped as adults to ward off predators and respond rapidly when a predator is in sight. [2]

Foraging in flocks

Group of black-capped chickadees feeding at a bird feeder. Black-capped Chickadee Poecile atricapillus2.JPG
Group of black-capped chickadees feeding at a bird feeder.

Bird species living in a flock are able to capture prey, likely injured, from an unsuccessful bird within its flock. [2] This behavior is known as the beater effect and is one of the benefits of birds foraging in a flock with other birds. [2]

It can be seen that birds in a flock may perform the information-sharing model. [2] In this situation the entire flock would search for food and the first to find a reliable food source will alert the flock and the entire group may benefit by this finding. [2] While this is an obvious benefit of the information-sharing model, the cost is that the social hierarchy of the flock may result in subordinate birds being denied food by those that are dominant. [2] Another cost is the possibility that some individuals may refuse to contribute in the search of food and instead simply wait for another member to find a food resource. [2] These individuals are known as producers and scroungers, respectively. [2]

An intricate hunting system can be seen in the Harris's hawk in which groups of 2–6 hunt a single prey together. [2] The group splits into smaller groups in which it then encloses on a prey, such as a rabbit, before it attacks it. [2] By hunting as a group the Harris's Hawk is able to hunt larger animals and decrease the amount of energy spent hunting while each hawk in the group is able to eat from the catch. [2]

Black sun

Flock of birds demonstrating the Sort Sol Sort sol pdfnet.jpg
Flock of birds demonstrating the Sort Sol

In the Denmark, there is a biannual phenomenon known as sort sol (Danish for "black sun"). [9] This is when flocks of European starlings gather in vast numbers, creating complex shapes against the sky during the spring. [9] It is during this time spent in Denmark that the European starlings spend time gathering food and resting as part of their migration journey. [9] By being in groups this large the European starlings are able to decrease their risk of predation by hawks. [10]

Related Research Articles

<span class="mw-page-title-main">Tit (bird)</span> Family of small passerine birds

The tits, chickadees, and titmice constitute the Paridae, a large family of small passerine birds which occur mainly in the Northern Hemisphere and Africa. Most were formerly classified in the genus Parus.

<span class="mw-page-title-main">Antbird</span> Passerine bird family found across subtropical and tropical Central and South America

The antbirds are a large passerine bird family, Thamnophilidae, found across subtropical and tropical Central and South America, from Mexico to Argentina. There are more than 230 species, known variously as antshrikes, antwrens, antvireos, fire-eyes, bare-eyes and bushbirds. They are related to the antthrushes and antpittas, the tapaculos, the gnateaters and the ovenbirds. Despite some species' common names, this family is not closely related to the wrens, vireos or shrikes.

<span class="mw-page-title-main">Black-capped chickadee</span> Species of small, non-migratory, North American passerine

The black-capped chickadee is a small, nonmigratory, North American passerine bird that lives in deciduous and mixed forests. It is a member of the Paridae family, also known as tits. It has a distinct black cap on its head, a black bib underneath, and white cheeks. It has a white belly, buff sides, and grey wings, back, and tail. The bird is well known for its vocalizations, including its fee-bee call and its chick-a-dee-dee-dee call, from which it derives its name.

<span class="mw-page-title-main">Foraging</span> Searching for wild food resources

Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavior of animals in response to the environment where the animal lives.

<span class="mw-page-title-main">Herd</span> Similar as Group

A herd is a social group of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is called herding. These animals are known as gregarious animals.

<span class="mw-page-title-main">Anti-predator adaptation</span> Defensive feature of prey for selective advantage

Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught.

<span class="mw-page-title-main">Flight zone</span>

The flight zone of an animal is the area surrounding an animal that if encroached upon by a potential predator or threat, including humans, will cause alarm and escape behavior. The flight zone is determined by the animal's flight distance, sometimes called flight initiation distance (FID) which extends horizontally from the animal and sometimes vertically. It may also be termed escape distance, alert distance, flush distance, and escape flight distance.

<span class="mw-page-title-main">Siberian jay</span> Species of bird

The Siberian jay is a small jay with a widespread distribution within the coniferous forests in North Eurasia. It has grey-brown plumage with a darker brown crown and a paler throat. It is rusty-red in a panel near the wing-bend, on the undertail coverts and on the sides of the tail. The sexes are similar. Although its habitat is being fragmented, it is a common bird with a very wide range so the International Union for Conservation of Nature has assessed its conservation status as being of "least concern".

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The Central American squirrel monkey, also known as the red-backed squirrel monkey, is a squirrel monkey species from the Pacific coast of Costa Rica and Panama. It is restricted to the northwestern tip of Panama near the border with Costa Rica, and the central and southern Pacific coast of Costa Rica, primarily in Manuel Antonio and Corcovado National Parks.

A mixed-species feeding flock, also termed a mixed-species foraging flock, mixed hunting party or informally bird wave, is a flock of usually insectivorous birds of different species that join each other and move together while foraging. These are different from feeding aggregations, which are congregations of several species of bird at areas of high food availability.

Interspecies communication is communication between different species of animals, plants, or microorganisms.

<span class="mw-page-title-main">Gleaning (birds)</span> Feeding behavior of plucking invertebrates from solid surfaces

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<span class="mw-page-title-main">Mobbing (animal behavior)</span> Antipredator adaptation in which individuals of prey species cooperatively attack a predator

Mobbing in animals is an antipredator adaptation in which individuals of prey species cooperatively attack or harass predator, usually to protect their offspring. A simple definition of mobbing is an assemblage of individuals around a potentially dangerous predator. This is most frequently seen in birds, though it is also known to occur in many other animals such as the meerkat and some bovines. While mobbing has evolved independently in many species, it only tends to be present in those whose young are frequently preyed upon. This behavior may complement cryptic adaptations in the offspring themselves, such as camouflage and hiding. Mobbing calls may be used to summon nearby individuals to cooperate in the attack.

<span class="mw-page-title-main">Communal roosting</span>

Communal roosting is an animal behavior where a group of individuals, typically of the same species, congregate in an area for a few hours based on an external signal and will return to the same site with the reappearance of the signal. Environmental signals are often responsible for this grouping, including nightfall, high tide, or rainfall. The distinction between communal roosting and cooperative breeding is the absence of chicks in communal roosts. While communal roosting is generally observed in birds, the behavior has also been seen in bats, primates, and insects. The size of these roosts can measure in the thousands to millions of individuals, especially among avian species.

<span class="mw-page-title-main">Collective animal behavior</span> Animal cognition

Collective animal behaviour is a form of social behavior involving the coordinated behavior of large groups of similar animals as well as emergent properties of these groups. This can include the costs and benefits of group membership, the transfer of information, decision-making process, locomotion and synchronization of the group. Studying the principles of collective animal behavior has relevance to human engineering problems through the philosophy of biomimetics. For instance, determining the rules by which an individual animal navigates relative to its neighbors in a group can lead to advances in the deployment and control of groups of swimming or flying micro-robots such as UAVs.

<span class="mw-page-title-main">Shoaling and schooling</span> In biology, any group of fish that stay together for social reasons

In biology, any group of fish that stay together for social reasons are shoaling, and if the group is swimming in the same direction in a coordinated manner, they are schooling. In common usage, the terms are sometimes used rather loosely. About one quarter of fish species shoal all their lives, and about one half shoal for part of their lives.

Vigilance, in the field of behavioural ecology, refers to an animal's monitoring of its surroundings in order to heighten awareness of predator presence. Vigilance is an important behaviour during foraging as animals must often venture away from the safety of shelter to find food. However, being vigilant comes at the expense of time spent feeding, so there is a trade-off between the two. The length of time animals devote to vigilance is dependent on many factors including predation risk and hunger.

<span class="mw-page-title-main">Avian foraging</span>

Avian foraging refers to the range of activities and behaviours exhibited by birds in their quest for food. In addition to their unique body adaptations, birds have a range of described behaviours that differ from the foraging behaviours of other animal groups. According to the foraging habitat, birds may be grouped into foraging guilds. Foraging includes a range of activities, starting with the search for food, making use of sensory abilities, and which may involve one or more birds either of a single or even of multiple species. This is followed by locomotion and movements to obtain or capture the food, followed by the processing or handling of the foods prior to ingestion. Like all organisms foraging entails balancing the energy spent and energy gained. The high metabolic rate of birds, among the highest in the homoeotherm groups, constrains them to ensure a net positive gain in energy and have led evolutionary ethologists to develop the idea of optimal foraging.

In ethology and evolutionary biology, group living is defined as individuals of the same species (conspecifics), maintaining spatial proximity with one another over time with mechanisms of social attraction. Solitary life in animals is considered to be the ancestral state of living; and group living has thus evolved independently in many species of animals. Therefore, species that form groups through social interaction will result in a group of individuals that gain an evolutionary advantage, such as increased protection against predators, access to potential mates, increased foraging efficiency and the access to social information.

References

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