Mobbing (animal behavior)

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American crows (Corvus brachyrhynchos) mobbing a red-tailed hawk (Buteo jamaicensis). Redtail hawk chased by crows 4391.jpg
American crows (Corvus brachyrhynchos) mobbing a red-tailed hawk (Buteo jamaicensis).

Mobbing in animals is an antipredator adaptation in which individuals of prey species cooperatively attack or harass a predator, usually to protect their offspring. A simple definition of mobbing is an assemblage of individuals around a potentially dangerous predator. [1] 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. [2] [3] While mobbing has evolved independently in many species, it only tends to be present in those whose young are frequently preyed upon. [2] 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.

Contents

Konrad Lorenz, in his book On Aggression (1966), attributed mobbing among birds and animals to instincts rooted in the Darwinian struggle to survive. In his view, humans are subject to similar innate impulses but capable of bringing them under rational control (see mobbing). [4]

In birds

A cattle tyrant (Machetornis rixosa) (right) mobbing a hawk Bem-te-vi e gaviao REFON.jpg
A cattle tyrant (Machetornis rixosa) (right) mobbing a hawk

Birds that breed in colonies such as gulls are widely seen to attack intruders, including encroaching humans. [5] In North America, the birds that most frequently engage in mobbing include mockingbirds, crows and jays, chickadees, terns, and blackbirds. Behavior includes flying about the intruder, dive bombing, loud squawking and defecating on the predator. Mobbing can also be used to obtain food, by driving larger birds and mammals away from a food source, or by harassing a bird with food. One bird might distract while others quickly steal food. Scavenging birds such as gulls frequently use this technique to steal food from humans nearby. 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. The black-headed gull is a species which aggressively engages intruding predators, such as carrion crows. Classic experiments on this species by Hans Kruuk involved placing hen eggs at intervals from a nesting colony, and recording the percentage of successful predation events as well as the probability of the crow being subjected to mobbing. [6] 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.

Crows mobbing a perched bald eagle (Haliaeetus leucocephalus) Crows Mobbing Bald Eagle 04.jpg
Crows mobbing a perched bald eagle (Haliaeetus leucocephalus)

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. [7]

Adaptationist hypotheses regarding why an organism should engage in such risky behavior have been suggested by Eberhard Curio, [8] 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, [9] 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. [10] Indeed, an intruding carrion crow can only avoid incoming attacks by facing its attackers, which prevents it from locating its target. [5]

Besides experimental research, the comparative method can also be employed to investigate hypotheses such as those given by Curio above. For example, not all gull species show mobbing behavior. The kittiwake nests on sheer cliffs that are almost completely inaccessible to predators, meaning its young are not at risk of predation like other gull species. [11] This is an example of divergent evolution.

Another hypothesis for mobbing behavior is known as the “attract the mightier hypothesis.” Within this hypothesis, prey species produce a mobbing call in order to attract stronger secondary predator to address the threat of the present primary predator. A study conducted by Fang et al., showed significant findings for this unproved functional thesis, utilizing three different call types for the prey species light-vented bulbuls, Pycnonotus sinensis: the typical call (TC, the control treatment), a mobbing call to a collared scops owl (the MtO treatment) and a mobbing call to a crested goshawk, Accipiter trivirgatus (the superior predator; the MtH treatment). [12]

Looking at variation in the behavioural responses of 22 different passerine species to a potential predator, the Eurasian Pygmy Owl, extent of mobbing was positively related with a species prevalence in the owls' diet. Furthermore, the intensity of mobbing was greater in autumn than spring. [13]

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 owls have cryptic plumage and hidden roosts which reduces this danger. [14]

Effect of environment on mobbing behavior

Environment has an effect on mobbing behavior as seen in a study conducted by Dagan & Izhaki (2019), wherein mobbing behavior was examined particularly observing the effects of Pine Forest structure. Their findings showed that mobbing behavior varied by season, i.e., high responses in the winter, and moderate response in the fall. [15] Additionally, the presence of a forest understory had a significant impact on mobbing behavior, i.e., the denser the understory vegetation, the more birds responded to mobbing calls. [15] That is to say, the presence of cover in the forest highly contributes to willingness to respond to the aforementioned call.    

In other animals

The occurrence of mobbing behavior across widely different taxa, including California ground squirrels, is evidence of convergent evolution. Squirrel vs snake.jpg
The occurrence of mobbing behavior across widely different taxa, including California ground squirrels, is evidence of convergent evolution.

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 evolution, where distantly related organisms evolve the same trait due to similar selection pressures. As mentioned, many bird species such as the swallows also mob predators, however more distantly related groups including mammals have been known to engage in this behavior. One example is the California ground squirrel, which distracts predators such as the rattlesnake and gopher snake from locating their nest burrows by kicking sand into their face, which disrupts the snake's sensory organs; for crotaline snakes, this includes the heat-detecting organs in the loreal pits. [16] This social species also uses alarm calls.

Some fish engage in mobbing; for example, bluegills sometimes attack snapping turtles. [1] Bluegills, which form large nesting colonies, were seen to attack both released and naturally occurring turtles, which may advertise their presence, drive the predator from the area, or aid in the transmission of predator recognition. Similarly, humpback whales are known to mob killer whales when the latter are attacking other species, including other cetacean species, seals, sea lions, and fish. [17]

There is a distinction though, between mobbing in animals, and fight-or-flight response. The former relies heavily on group dynamics, whereas the latter’s central focus conceptually is on that of the individual and their offspring in some cases. A study conducted by Adamo & McKee (2017) examining the cricket Gryllus texensis showcases this by activating high predation risk repeatedly to examine how animals in general perceive such risks. [18] Based on perceived threat, crickets took action to save their own self or made attempt to preserve offspring.

Mobbing calls

The great tit (Parus major), a passerine bird, employs both mobbing behavior and alarm calls. Birds through the year (6025491141).jpg
The great tit (Parus major), a passerine bird, employs both mobbing behavior and alarm calls.

Mobbing calls are signals made by the mobbing species while harassing a predator. These differ from alarm calls, 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, [5] and carries over long distances. However, when prey species are in flight, they employ an alarm signal in the 7–8 kHz range. This call is less effective at traveling great distances, but is much more difficult for both owls and hawks to hear (and detect the direction from which the call came). [19] In the case of the alarm call, it could be 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.

Furthermore, bird vocalizations vary acoustically as a byproduct of adapting to the environment, according to the acoustic adaptation hypothesis. In a study by Billings (2018) examining, specifically the low-frequency acoustic structure of mobbing calls across habitat types (closed, open, and urban) in three passerine families (Corvidae, Icteridae, Turdidae), it was discovered that the size of the bird was a factor in the variation of mobbing calls. Additionally, species in closed and urban habitats had lower energy and lower low frequencies in their mobbing calls, respectively. [20]

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. [21]

Evolution

African buffalo herd confronting a lion Serengeti liontree buffl.jpg
African buffalo herd confronting a lion

The evolution of mobbing behavior can be explained using evolutionarily stable strategies, which are in turn based on game theory. [22]

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.

Mobbing behavior varies in intensity depending on the perceived threat of a predator according to a study done by Dutour et al. (2016). [23] However, particularly in terms of its surfacing in avian species, it is accepted to be the byproduct of mutualism, rather than reciprocal altruism according to Russell & Wright (2009). [24]

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 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. [25] [26]

Another interpretation involves the use of signalling theory, and possibly 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. [27]

Related Research Articles

<span class="mw-page-title-main">Black-headed gull</span> Species of bird

The black-headed gull is a small gull that breeds in much of the Palearctic including Europe and also in coastal eastern Canada. Most of the population is migratory and winters further south, but some birds reside in the milder westernmost areas of Europe. The species also occurs in smaller numbers in northeastern North America, where it was formerly known as the common black-headed gull.

<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">Great black-backed gull</span> Species of bird

The great black-backed gull is the largest member of the gull family. Described by the Cornell Lab of Ornithology as "the king of the Atlantic waterfront", it is a very aggressive hunter, pirate, and scavenger. It breeds on the European and North American coasts and islands of the North Atlantic and is fairly sedentary, though some move farther south or inland to large lakes and reservoirs. The adult great black-backed gull has a white head, neck and underparts, dark grey wings and back, pink legs and yellow bill.

<span class="mw-page-title-main">Rough-legged buzzard</span> Species of bird

The rough-legged buzzard (Europe) or rough-legged hawk is a medium-large bird of prey. It is found in Arctic and Subarctic regions of North America, Europe, and Russia during the breeding season and migrates south for the winter. It was traditionally also known as the rough-legged falcon in such works as John James Audubon's The Birds of America.

<span class="mw-page-title-main">Tree swallow</span> Species of bird in the Americas

The tree swallow is a migratory bird of the family Hirundinidae. Found in the Americas, the tree swallow was first described in 1807 by French ornithologist Louis Vieillot as Hirundo bicolor. It has since been moved to its current genus, Tachycineta, within which its phylogenetic placement is debated. The tree swallow has glossy blue-green upperparts, with the exception of the blackish wings and tail, and white underparts. The bill is black, the eyes dark brown, and the legs and feet pale brown. The female is generally duller than the male, and the first-year female has mostly brown upperparts, with some blue feathers. Juveniles have brown upperparts, and grey-brown-washed breasts. The tree swallow breeds in the US and Canada. It winters along southern US coasts south, along the Gulf Coast, to Panama and the northwestern coast of South America, and in the West Indies.

<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">Chacma baboon</span> Species of baboon from the Old World monkey family

The chacma baboon, also known as the Cape baboon, is, like all other baboons, from the Old World monkey family. It is one of the largest of all monkeys. Located primarily in southern Africa, the chacma baboon has a wide variety of social behaviours, including a dominance hierarchy, collective foraging, adoption of young by females, and friendship pairings. These behaviors form parts of a complex evolutionary ecology. In general, the species is not threatened, but human population pressure has increased contact between humans and baboons. Hunting, trapping, and accidents kill or remove many baboons from the wild, thereby reducing baboon numbers and disrupting their social structure.

<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.

Apostatic selection is a form of negative frequency-dependent selection. It describes the survival of individual prey animals that are different from their species in a way that makes it more likely for them to be ignored by their predators. It operates on polymorphic species, species which have different forms. In apostatic selection, the common forms of a species are preyed on more than the rarer forms, giving the rare forms a selective advantage in the population. It has also been discussed that apostatic selection acts to stabilize prey polymorphisms.

<span class="mw-page-title-main">Flock (birds)</span> A group of individual birds travelling together

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

<span class="mw-page-title-main">Bird colony</span> Large congregation of birds at a particular location

A bird colony is a large congregation of individuals of one or more species of bird that nest or roost in proximity at a particular location. Many kinds of birds are known to congregate in groups of varying size; a congregation of nesting birds is called a breeding colony. Colonial nesting birds include seabirds such as auks and albatrosses; wetland species such as herons; and a few passerines such as weaverbirds, certain blackbirds, and some swallows. A group of birds congregating for rest is called a communal roost. Evidence of colonial nesting has been found in non-neornithine birds (Enantiornithes), in sediments from the Late Cretaceous (Maastrichtian) of Romania.

<span class="mw-page-title-main">Nesting instinct</span> Instinct in pregnant animals related to estradiol

Nesting behavior refers to an instinct in animals during reproduction to prepare a place with optimal conditions for offspring. The nesting place provides protection against predators and competitors that mean to exploit or kill offspring. It also provides protection against the physical environment.

<span class="mw-page-title-main">Distraction display</span>

Distraction displays, also known as diversionary displays, or paratrepsis are anti-predator behaviors used to attract the attention of an enemy away from something, typically the nest or young, that is being protected by a parent. Distraction displays are sometimes classified more generically under "nest protection behaviors" along with aggressive displays such as mobbing. These displays have been studied most extensively in bird species, but also have been documented in populations of stickleback fish and in some mammal species.

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

Clutch size refers to the number of eggs laid in a single brood by a nesting pair of birds. The numbers laid by a particular species in a given location are usually well defined by evolutionary trade-offs with many factors involved, including resource availability and energetic constraints. Several patterns of variation have been noted and the relationship between latitude and clutch size has been a topic of interest in avian reproduction and evolution. David Lack and R.E. Moreau were among the first to investigate the effect of latitude on the number of eggs per nest. Since Lack's first paper in the mid-1940s there has been extensive research on the pattern of increasing clutch size with increasing latitude. The proximate and ultimate causes for this pattern have been a subject of intense debate involving the development of ideas on group, individual, and gene-centric views of selection.

<span class="mw-page-title-main">Begging in animals</span>

Begging in animals is when an animal solicits being given resources by another animal. This is usually a young animal soliciting food from their parents, brood hosts or other adults. However, the resource is sometimes non-food related or may be solicited by adult animals. Begging behavior is most widely studied in birds, however, mammals, amphibians, and invertebrates perform begging displays. Generally in food solicitation, begging behavior is instinctive, although in some instances it is learned.

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">Eurasian goshawk</span> Species of bird

The Eurasian goshawk is a species of medium-large bird of prey in the family Accipitridae, a family which also includes other extant diurnal raptors, such as eagles, buzzards and harriers. As a species in the genus Accipiter, the goshawk is often considered a "true hawk". The scientific name is Latin; Accipiter is "hawk", from accipere, "to grasp", and gentilis is "noble" or "gentle" because in the Middle Ages only the nobility were permitted to fly goshawks for falconry.

<span class="mw-page-title-main">Egg predation</span> Feeding strategy for many animals

Egg predation or ovivory is a feeding strategy in many groups of animals (ovivores) in which they consume eggs. Since a fertilized egg represents a complete organism at one stage of its life cycle, eating an egg is a form of predation, the killing of another organism for food.

<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.

Dietary conservatism is a foraging strategy in which individuals show a prolonged reluctance to eat novel foods, even after neophobia has been overcome. Within any given population of foragers, some will be conservative and some will be adventurous, an alternative strategy in which individuals readily accept novel food immediately after neophobia has waned. Dietary conservatism and neophobia are however distinct processes, distinguished by the persistence of an individual's reluctance to eat over repeated encounters with novel food and over long time periods.

References

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  2. 1 2 "Cows kill leopard in Maharashtra". The Hindu. PTI. 2018-07-13. ISSN   0971-751X . Retrieved 2018-08-12.
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  4. ↑ Kenneth Westheus Mobbing Archived 2011-08-12 at the Wayback Machine . uwaterloo.ca
  5. 1 2 3 Alcock, John (1998). Animal Behavior: An Evolutionary Approach (6th ed.). Sunderland: Sinauer Associates. ISBN   978-0-87893-009-8.
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  14. ↑ Hendrichsen, Ditte K.; Christiansen, Peter; Nielsen, Elsemarie K.; Dabelsteen, Torben; Sunde, Peter (2006). "Exposure affects the risk of an owl being mobbed – experimental evidence". Journal of Avian Biology. 37 (1): 13–18. doi:10.1111/j.2005.0908-8857.03658.x.
  15. 1 2 Dagan, Uzi; Izhaki, Ido (2019-09-03). "The Effect of Pine Forest Structure on Bird-Mobbing Behavior: From Individual Response to Community Composition". Forests. 10 (9): 762. doi: 10.3390/f10090762 . ISSN   1999-4907.
  16. ↑ Coss, Richard G.; Biardi, J. E. (1997). "Individual Variation in the Antisnake Behavior of California Ground Squirrels (Spermophilus beecheyi)". Journal of Mammalogy. 78 (2): 294–310. doi: 10.2307/1382883 . JSTOR   1382883.
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  18. ↑ Adamo, S.A.; McKee, R. (December 2017). "Differential effects of predator cues versus activation of fight-or-flight behaviour on reproduction in the cricket Gryllus texensis". Animal Behaviour. 134: 1–8. doi:10.1016/j.anbehav.2017.09.027. S2CID   53153442.
  19. ↑ Brown, C. H. (1982). "Ventriloquial and locatable vocalizations in birds". Zeitschrift für Tierpsychologie. 59 (4): 338–350. doi:10.1111/j.1439-0310.1982.tb00346.x.
  20. ↑ Billings, Alexis C. (April 2018). "The low-frequency acoustic structure of mobbing calls differs across habitat types in three passerine families". Animal Behaviour. 138: 39–49. doi: 10.1016/j.anbehav.2018.02.001 . S2CID   53182553.
  21. ↑ Leger, Daniel W.; Laura F. Carroll (1981). "Mobbing calls of the Phainopepla" (PDF). The Condor. 83 (4): 377–380. doi:10.2307/1367509. JSTOR   1367509. S2CID   49558729 . Retrieved 2007-06-12.
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  24. ↑ Russell, Andrew F.; Wright, Jonathan (January 2009). "Avian mobbing: byproduct mutualism not reciprocal altruism". Trends in Ecology & Evolution. 24 (1): 3–5. doi:10.1016/j.tree.2008.09.003. PMID   19022524.
  25. ↑ Kelly, Kevin (1994). Out of control: the new biology of machines, social systems and the economic world. Boston: Addison-Wesley. ISBN   978-0-201-48340-6.
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  27. ↑ Arnold, K. E. (2000). "Group Mobbing Behaviour and Nest Defence in a Cooperatively Breeding Australian Bird" (PDF). Ethology. 106 (5): 385–393. Bibcode:2000Ethol.106..385A. doi:10.1046/j.1439-0310.2000.00545.x.
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