Mobbing behavior
Encyclopedia
Mobbing in animals is an antipredator behavior which occurs when individuals of a certain species mob a predator by cooperatively attacking or harassing it, 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 avian
species, though it is also known to occur in many other animal
s such as the Meerkat
. 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.
Konrad Lorenz
, in his book entitled On Aggression (1966), first described mobbing among birds and animals, attributing it to instincts rooted in the Darwinian struggle to survive. In his view, we humans are subject to similar innate impulses but capable of bringing them under rational control (see mobbing
).
Birds that breed in colonies such as gull
s are widely seen to attack intruders, including encroaching humans. The birds that most frequently engage in mobbing include mockingbirds, jays, chickadees, and blackbirds. Through mobbing, mockingbird
s can effectively force a cat or dog to seek something less troublesome. One mockingbird might fly in front of the cat or dog, enticing a common predator upon birds to lunge, while another pecks at the cat or dog from behind to inflict a sharp pain that forces the predator to hesitate when it encounters mockingbirds. Behavior includes flying about the intruder, dive bombing, loud squawking and defecating
on the predator. Mobbing can also be used to drive larger birds and mammals away from a food source. One bird might distract while others quickly steal food. A flock of birds might drive a powerful animal away from food. Costs of mobbing behavior include the risk of engaging with predators, as well as energy expended in the process. Black-headed Gull
s are one species which aggressively engages intruding predators, such as Carrion Crow
s. Classic experiments on this species by Hans Kruuk involved placing hen eggs at intervals from a nest
ing colony, and recording the percentage of successful predation events as well as the probability of the crow being subjected to mobbing. The results showed decreasing mobbing with increased distance from the nest, which was correlated with increased predation success. Mobbing may function by reducing the predator's ability to locate nests (as a distraction) since predators cannot focus on locating eggs while they are under attack.
Besides the ability to drive the predator away, mobbing also draws attention to the predator, making stealth attacks impossible. Mobbing plays a critical role in the identification of predators and inter-generational learning about predator identification. Reintroduction of species is often unsuccessful, because the established population lacks this cultural knowledge of how to identify local predators. Scientists are exploring ways to train populations to identify and respond to predators before releasing them into the wild.
Adaptationist hypotheses regarding why an organism should engage in such risky behavior have been suggested by Eberhard Curio, including advertising their physical fitness and hence uncatchability (much like stotting
behavior in gazelles), distracting predators from finding their offspring, warning
their offspring, luring the predator away, allowing offspring to learn
to recognize the predator species, directly injuring
the predator or attracting a predator of the predator itself. The much lower frequency of attacks between nesting seasons suggests such behavior may have evolved due to its benefit for the mobber's young. Niko Tinbergen argued that the mobbing was a source of confusion
to gull chick predators, distracting them from searching for prey . Indeed, an intruding carrion crow can only avoid incoming attacks by facing its attackers, which prevents it from locating its target.
Besides experiment
al research, the comparative method
can also be employed to investigate hypotheses such as those given by Curio above. For example, closely related
species such as the Kittiwake
do not show mobbing behavior. The kittiwake's cliff
nests are almost completely inaccessible to possible predators due to gusty wind
s and sheer cliffs, meaning its young are not at risk to predation like the Black-headed Gull. This is an example of an evolutionary pattern known as divergent evolution
.
Mobbing is thought to carry risks to roosting predators, including potential harm from the mobbing birds, or attracting larger, more dangerous predators. Birds at risk of mobbing such as owl
s have cryptic plumage
and hidden roosts to reduce this danger.
, where distantly related organisms evolve the same trait due to similar selection pressures. As mentioned, many bird species such as the swallow
s also show mobbing of predators, however even more distantly related species including mammal
s have been known to engage in this behavior. One example is California ground squirrel
s, which are known to distract predators such as the rattlesnake
and gopher snake from locating their nest burrow
s by kicking sand into their eyes. This social
species also uses alarm calls.
Mobbing has also been observed in fish
. For example, bluegill
s have been seen to attack snapping turtles. Bluegills, which form large nesting colonies, were seen to attack both released and naturally occurring turtles, which may function to advertise their presence, drive the predator from the area, or aid in cultural transmission of predator recognition.
.jpg)
Mobbing calls are signals made by the mobbing species while harassing a predator. These differ from alarm call
s, which allow con-specifics to escape from the predator. The Great Tit
, a European songbird
uses such a signal to call on nearby birds to harass a perched bird of prey
, such as an owl. This call occurs in the 4.5kHz range, and is effective in traveling long distances. However, when their prey are in flight, they employ an alarm signal in the 7–8 kHz range. This call is less effective at travelling great distances, but is much more difficult for both owls and hawks to hear (and detect the direction from which the call came). In the case of the alarm call, it is disadvantageous to the sender if the predator picks up on the signal, hence selection
has favored those birds able to hear and employ calls in this higher frequency range.
Mobbing calls may also be part of an animal's arsenal in harassing the predator. Studies of Phainopepla
mobbing calls indicate it may serve to enhance the swooping attack on the predators, including Scrub Jays. In this species, the mobbing call is smoothly upsweeping, and is made when swooping down in an arc beside the predator. This call was also heard during agonistic behavior
interactions with conspecifics, and may serve additionally or alternatively as an alarm call to their mate.
, which are in turn based on game theory
.
Mobbing involves risks (costs) to the individual and benefits (payoffs) to the individual and others. The individuals themselves are often genetically related, and mobbing is increasingly studied with the gene-centered view of evolution
by considering inclusive fitness
(the carrying on of one's genes through one's family members), rather than merely benefit to the individual.
By cooperating to successfully drive away predators all individuals involved increase their chances of survival and reproduction. An individual stands little chance against a larger predator, but when a large group is involved, the risk to each group member is minimized. By being in a large group, the risk for a particular individual is reduced or diluted. This so-called dilution effect proposed by W. D. Hamilton
is another way of explaining the benefits of cooperation by selfish individuals. Lanchester's laws
also provide an insight into the advantages of attacking in a large group rather than individually.
Another interpretation involves the use of the handicap principle
. Here the idea is that a mobbing bird, by apparently putting itself at risk, displays its status and health so as to be preferred by potential partners
.
Offspring
In biology, offspring is the product of reproduction, of a new organism produced by one or more parents.Collective offspring may be known as a brood or progeny in a more general way...
. A simple definition of mobbing is an assemblage of individuals around a potentially dangerous predator. This is most frequently seen in avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
species, though it is also known to occur in many other animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s such as the Meerkat
Meerkat
The meerkat or suricate, Suricata suricatta, is a small mammal belonging to the mongoose family. Meerkats live in all parts of the Kalahari Desert in Botswana, in much of the Namib Desert in Namibia and southwestern Angola, and in South Africa. A group of meerkats is called a "mob", "gang" or "clan"...
. 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
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
adaptations in the offspring themselves, such as camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
and hiding. Mobbing calls may be used to summon nearby individuals to cooperate
Co-operation (evolution)
Co-operation or co-operative behaviours are terms used to describe behaviours by organisms which are beneficial to other organisms, and are selected for on that basis. Under this definition, altruism is a form of co-operation in which there is no direct benefit to the actor...
in the attack.
Konrad Lorenz
Konrad Lorenz
Konrad Zacharias Lorenz was an Austrian zoologist, ethologist, and ornithologist. He shared the 1973 Nobel Prize with Nikolaas Tinbergen and Karl von Frisch...
, in his book entitled On Aggression (1966), first described mobbing among birds and animals, attributing it to instincts rooted in the Darwinian struggle to survive. In his view, we humans are subject to similar innate impulses but capable of bringing them under rational control (see mobbing
Mobbing
Mobbing in the context of human beings either means bullying of an individual by a group in any context. Identified as emotional abuse in the workplace, such as "ganging up" by co-workers, subordinates or superiors, to force someone out of the workplace through rumor, innuendo, intimidation,...
).
In birds
Gull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
s are widely seen to attack intruders, including encroaching humans. The birds that most frequently engage in mobbing include mockingbirds, jays, chickadees, and blackbirds. Through mobbing, mockingbird
Mockingbird
Mockingbirds are a group of New World passerine birds from the Mimidae family. They are best known for the habit of some species mimicking the songs of other birds and the sounds of insects and amphibians, often loudly and in rapid succession. There are about 17 species in three genera...
s can effectively force a cat or dog to seek something less troublesome. One mockingbird might fly in front of the cat or dog, enticing a common predator upon birds to lunge, while another pecks at the cat or dog from behind to inflict a sharp pain that forces the predator to hesitate when it encounters mockingbirds. Behavior includes flying about the intruder, dive bombing, loud squawking and defecating
Defecation
Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum...
on the predator. Mobbing can also be used to drive larger birds and mammals away from a food source. One bird might distract while others quickly steal food. A flock of birds might drive a powerful animal away from food. Costs of mobbing behavior include the risk of engaging with predators, as well as energy expended in the process. Black-headed Gull
Black-headed Gull
The Black-headed Gull is a small gull which breeds in much of Europe and Asia, and also in coastal eastern Canada. Most of the population is migratory, wintering further south, but some birds in the milder westernmost areas of Europe are resident...
s are one species which aggressively engages intruding predators, such as Carrion Crow
Carrion Crow
The Carrion Crow is a member of the passerine order of birds and the crow family which is native to western Europe and eastern Asia.-Taxonomy:...
s. Classic experiments on this species by Hans Kruuk involved placing hen eggs at intervals from a nest
Nest
A nest is a place of refuge to hold an animal's eggs or provide a place to live or raise offspring. They are usually made of some organic material such as twigs, grass, and leaves; or may simply be a depression in the ground, or a hole in a tree, rock or building...
ing colony, and recording the percentage of successful predation events as well as the probability of the crow being subjected to mobbing. The results showed decreasing mobbing with increased distance from the nest, which was correlated with increased predation success. Mobbing may function by reducing the predator's ability to locate nests (as a distraction) since predators cannot focus on locating eggs while they are under attack.
Besides the ability to drive the predator away, mobbing also draws attention to the predator, making stealth attacks impossible. Mobbing plays a critical role in the identification of predators and inter-generational learning about predator identification. Reintroduction of species is often unsuccessful, because the established population lacks this cultural knowledge of how to identify local predators. Scientists are exploring ways to train populations to identify and respond to predators before releasing them into the wild.
Adaptationist hypotheses regarding why an organism should engage in such risky behavior have been suggested by Eberhard Curio, including advertising their physical fitness and hence uncatchability (much like stotting
Stotting
Stotting is a gait of quadrupeds, particularly gazelles , involving jumping high into the air by lifting all four feet off the ground simultaneously. This may occur during pursuit by a predator...
behavior in gazelles), distracting predators from finding their offspring, warning
Animal communication
Animal communication is any behavior on the part of one animal that has an effect on the current or future behaviour of another animal. The study of animal communication, is sometimes called Zoosemiotics has played an important part in the...
their offspring, luring the predator away, allowing offspring to learn
LEARN
LEARN may refer to:* Law Enforcement Agency Resource Network, a website run by the Anti-Defamation League* LEARN diet, a brand name diet product...
to recognize the predator species, directly injuring
Injury
-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...
the predator or attracting a predator of the predator itself. The much lower frequency of attacks between nesting seasons suggests such behavior may have evolved due to its benefit for the mobber's young. Niko Tinbergen argued that the mobbing was a source of confusion
ConFusion
ConFusion is an annual science fiction convention organized by the Stilyagi Air Corps and its parent organization, the Ann Arbor Science Fiction Association. Commonly, it is held the third weekend of January. It is the oldest science fiction convention in Michigan, a regional, general SF con...
to gull chick predators, distracting them from searching for prey . Indeed, an intruding carrion crow can only avoid incoming attacks by facing its attackers, which prevents it from locating its target.
Besides experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
al research, the comparative method
Phylogenetic comparative methods
Phylogenetic comparative methods use information on the evolutionary relationships of organisms to compare species...
can also be employed to investigate hypotheses such as those given by Curio above. For example, closely related
Common descent
In evolutionary biology, a group of organisms share common descent if they have a common ancestor. There is strong quantitative support for the theory that all living organisms on Earth are descended from a common ancestor....
species such as the Kittiwake
Kittiwake
The kittiwakes are two closely related seabird species in the gull family Laridae, the Black-legged Kittiwake and the Red-legged Kittiwake . The epithets "Black-legged" and "Red-legged" are used to distinguish the two species in North America, but in Europe, where R...
do not show mobbing behavior. The kittiwake's cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
nests are almost completely inaccessible to possible predators due to gusty wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
s and sheer cliffs, meaning its young are not at risk to predation like the Black-headed Gull. This is an example of an evolutionary pattern known as divergent evolution
Divergent evolution
Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation...
.
Mobbing is thought to carry risks to roosting predators, including potential harm from the mobbing birds, or attracting larger, more dangerous predators. Birds at risk of mobbing such as owl
Owl
Owls are a group of birds that belong to the order Strigiformes, constituting 200 bird of prey species. Most are solitary and nocturnal, with some exceptions . Owls hunt mostly small mammals, insects, and other birds, although a few species specialize in hunting fish...
s have cryptic plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
and hidden roosts to reduce this danger.
In other animals
Another way the comparative method can be used here is by comparing gulls with distantly related organisms. This approach relies on the existence of convergent evolutionConvergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
, where distantly related organisms evolve the same trait due to similar selection pressures. As mentioned, many bird species such as the swallow
Swallow
The swallows and martins are a group of passerine birds in the family Hirundinidae which are characterised by their adaptation to aerial feeding...
s also show mobbing of predators, however even more distantly related species including mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s have been known to engage in this behavior. One example is California ground squirrel
California Ground Squirrel
The California ground squirrel , is a common and easily observed ground squirrel of the western United States and the Baja California peninsula; it is common in Oregon and California and its range has relatively recently extended into Washington and northwestern Nevada...
s, which are known to distract predators such as the rattlesnake
Rattlesnake
Rattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae . There are 32 known species of rattlesnake, with between 65-70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to Central...
and gopher snake from locating their nest burrow
Burrow
A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
s by kicking sand into their eyes. This social
Social behavior
In physics, physiology and sociology, social behavior is behavior directed towards society, or taking place between, members of the same species. Behavior such as predation which involves members of different species is not social...
species also uses alarm calls.
Mobbing has also been observed in fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
. For example, bluegill
Bluegill
The Bluegill is a species of freshwater fish sometimes referred to as bream, brim, or copper nose. It is a member of the sunfish family Centrarchidae of the order Perciformes.-Range and distribution:...
s have been seen to attack snapping turtles. Bluegills, which form large nesting colonies, were seen to attack both released and naturally occurring turtles, which may function to advertise their presence, drive the predator from the area, or aid in cultural transmission of predator recognition.
Mobbing calls
Alarm call
In the field of animal communication, an alarm signal is an antipredator adaptation referring to various signals emitted by social animals in response to danger. Many primates and birds have elaborate alarm calls for warning conspecifics of approaching predators. For example, the characteristic...
s, which allow con-specifics to escape from the predator. The Great Tit
Great Tit
The Great Tit is a passerine bird in the tit family Paridae. It is a widespread and common species throughout Europe, the Middle East, Central and Northern Asia, and parts of North Africa in any sort of woodland. It is generally resident, and most Great Tits do not migrate except in extremely...
, a European songbird
Songbird
A songbird is a bird belonging to the suborder Passeri of the perching birds . Another name that is sometimes seen as scientific or vernacular name is Oscines, from Latin oscen, "a songbird"...
uses such a signal to call on nearby birds to harass a perched bird of prey
Bird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....
, such as an owl. This call occurs in the 4.5kHz range, and is effective in traveling long distances. However, when their prey are in flight, they employ an alarm signal in the 7–8 kHz range. This call is less effective at travelling great distances, but is much more difficult for both owls and hawks to hear (and detect the direction from which the call came). In the case of the alarm call, it is disadvantageous to the sender if the predator picks up on the signal, hence selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
has favored those birds able to hear and employ calls in this higher frequency range.
Mobbing calls may also be part of an animal's arsenal in harassing the predator. Studies of Phainopepla
Phainopepla
The Phainopepla is the most northerly representative of the mainly tropical Central American family Ptilogonatidae, the silky flycatchers.-Description:...
mobbing calls indicate it may serve to enhance the swooping attack on the predators, including Scrub Jays. In this species, the mobbing call is smoothly upsweeping, and is made when swooping down in an arc beside the predator. This call was also heard during agonistic behavior
Agonistic behaviour
In ethology, agonistic behaviour is any social behaviour related to fighting. Thus it is broader than aggressive behaviour because it includes not only actual aggression but also threats, displays, retreats, placating aggressors, and conciliation. The term was coined by Scott and Fredericson in 1951...
interactions with conspecifics, and may serve additionally or alternatively as an alarm call to their mate.
Evolution
The evolution of mobbing behavior is explained using evolutionarily stable strategiesEvolutionarily stable strategy
In game theory and behavioural ecology, an evolutionarily stable strategy , which is sometimes also called an evolutionary stable strategy, is a strategy which, if adopted by a population of players, cannot be invaded by any alternative strategy that is initially rare. An ESS is an equilibrium...
, which are in turn based on game theory
Game theory
Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...
.
Mobbing involves risks (costs) to the individual and benefits (payoffs) to the individual and others. The individuals themselves are often genetically related, and mobbing is increasingly studied with the gene-centered view of evolution
Gene-centered view of evolution
The gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution occurs through the differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation, with gene defined as...
by considering inclusive fitness
Inclusive fitness
In evolutionary biology and evolutionary psychology, the inclusive fitness of an organism is the sum of its classical fitness and the number of equivalents of its own offspring it can add to the population by supporting others...
(the carrying on of one's genes through one's family members), rather than merely benefit to the individual.
By cooperating to successfully drive away predators all individuals involved increase their chances of survival and reproduction. An individual stands little chance against a larger predator, but when a large group is involved, the risk to each group member is minimized. By being in a large group, the risk for a particular individual is reduced or diluted. This so-called dilution effect proposed by W. D. Hamilton
W. D. Hamilton
William Donald Hamilton FRS was a British evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century....
is another way of explaining the benefits of cooperation by selfish individuals. Lanchester's laws
Lanchester's laws
Lanchester's laws are mathematical formulae for calculating the relative strengths of a predator/prey pair. This article is concerned with military forces....
also provide an insight into the advantages of attacking in a large group rather than individually.
Another interpretation involves the use of the handicap principle
Handicap principle
The handicap principle is a hypothesis originally proposed in 1975 by biologist Amotz Zahavi to explain how evolution may lead to "honest" or reliable signaling between animals who have an obvious motivation to bluff or deceive each other...
. Here the idea is that a mobbing bird, by apparently putting itself at risk, displays its status and health so as to be preferred by potential partners
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
.
External links
- Interspecific reciprocity explains mobbing behaviour of the breeding chaffinches, Fringilla coelebs Paper by Indrikis Krams and Tatjana Krama (PDF)
- Nature Photography - Using mobbing behavior in photographyPhotographyPhotography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...