Vigilance (behavioural ecology)

Last updated

Vigilance, in the field of behavioural ecology, refers to an animal's examination 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.

Contents

Vigilance is often observed in animals that forage in groups, such as yellow-eyed juncos (Junco phaeonutus) and meerkats (Suricata suricatta). Foraging in groups dilutes an individual's risk of predation, and allows them to reduce their own vigilance while the vigilance of the group is maintained. [1] Alarm signals may be used to alert the group to the presence of predators. Groups of some species have at least one individual on sentry duty who looks out for predators on a perch while the rest of the group forages. [1]

Feeding and predation risk trade-off

Vigilance and feeding (both searching for and handling food) are generally mutually exclusive activities, leading to foragers facing a trade-off between energy intake and safety from predation. As time allocated to scanning reduces the time spent feeding, vigilant individuals must devote more time on foraging to obtain the required food intake. [2] This impedes on other activities in their time budget such as mating and prolongs their exposure to predation as foraging occurs away from shelter. [2] When foraging time is limited, vigilant animals are left with a reduced energy intake. [2]

Optimality models can be used to predict foraging decisions of an animal based on costs (predation risk, starvation) and benefits (safety, food), which are also affected by physiology such as hunger levels. [1]

A grey squirrel (Sciurus carolinensis) feeding in the safety of a tree to minimise exposure to predators during food handling Eastern Grey Squirrel in St James's Park, London - Nov 2006 edit.jpg
A grey squirrel (Sciurus carolinensis) feeding in the safety of a tree to minimise exposure to predators during food handling

Grey squirrels (Sciurus carolinensis) alter their behaviour according to the relative costs and benefits when foraging in the open. [3] Small food items are consumed immediately to maximise energy intake, as they require little handling time so the cost of predation risk is low. [3] Large items that require a long handling time, and hence time exposed to predators, are carried back to the safety of a tree to minimise predation risk. [3] Although there is an energetic cost to transporting food, large food items have a high contribution to nutrient intake so the cost outweighs the benefits. [3]

The overall predation risk is a function of the abundance, activity and ability of predators to detect the forager, as well as the likelihood that the forager can escape the predator if it is not vigilant. [4] Animals prioritise vigilance over feeding when the predation risk is high. For example, yellow-eyed juncos spend more time scanning for predators when a potential predator, a Harris's hawk (Parabuteo unicinctus), is present compared to when the hawk is absent. [5]

Another factor that influences vigilance is the benefit that is expected from foraging in the absence of predation. [4] This is dependent on the quality of the food as well as the energetic state of the individual. If there is much to be gained from feeding, foragers may forgo vigilance. Similarly, if hungry animals have a higher chance of dying from starvation than from predation, it is more beneficial to sacrifice vigilance to fulfill their energy requirements. When three-spined sticklebacks (Gasterosteus aculeatus) are deprived of food, they prefer to feed in locations with a high density of water fleas. [6] The cost to this choice is that the sticklebacks must concentrate on picking out the prey due to the 'predator confusion effect' where many moving targets make it difficult for predators to pick out individual prey. [6] This choice means that the sticklebacks are less able to scan for predators however the risk of starvation is relatively higher than the risk of predation. [6] Similarly, juncos that have been deprived of food exhibit lower levels of vigilance, instead focusing on rapid feeding which is a behaviour incompatible with scanning. [7]

Habitat and food choice

The state of an animal can change due to its behaviour and vice versa due to the dynamic feedback between foraging, body reserves and predation risk. [1] The feedback can influence an individual's choice of where, when and what to feed on. If the predation risk is so great that an animal must maintain a level of vigilance that drastically inhibits feeding, it may opt for an alternative.

For example, the bluegill sunfish (Lepomis macrochirus) has the choice of foraging on plankton in the safety of reeds or on benthic invertebrates which are a better quality food source. [8] When a predator (the largemouth bass) is present, smaller sunfish spend the majority of their time foraging in the reeds despite this choice reducing their food intake and seasonal growth rate. [8] Sunfish that are too large to be eaten by the bass forage almost entirely on benthos. Although staying in the reeds means a slower growth rate and a longer period of being a size vulnerable to predators, for maximum survival sunfish choose to remain in the reeds feeding on plankton until they reach a certain size and then leave to feed on benthos. [8]

Nocturnal animals alter the timing of their foraging based on the level of light – avoiding feeding when the moonlight is bright as this is when predation risk is highest. [9]

A raised head is the most commonly used indicator of vigilance, as many animals require their heads to be lowered to search for and handle food. [10] Different foods require different handling that can affect the amount of vigilance an animal can maintain. Seeds without husks, for example, require little handling by birds so are rapidly pecked up with the birds head down which is incompatible with vigilance. [11] In situations of high predation risk, animals may choose foods that can be foraged while maintaining vigilance. When dark-eyed juncos (Junco hymenalis) feed in small flocks, they prefer to feed on larger pieces of food than when they are part of a larger flock. [11] As individuals in smaller flocks have a greater need to be vigilant (see more in Vigilance in groups), large pieces of food are more beneficial as they require a longer handling time that can be simultaneously spent scanning, whereas birds feeding on small pieces must intermittently stop foraging to scan their environment. [11]

Vigilance in groups

Both solitary and group foraging come with a variety of costs and benefits but for many animals, foraging in a group is the most optimal strategy. Among the many benefits of group foraging, reduction of predation risk by improved vigilance is one. Wood pigeons (Columba palumbus) in large flocks are more able to escape predation by goshawks because they are able to spot them and fly away more quickly than they would individually. [1] This is because in larger flocks, it is more likely that one bird will notice the hawk sooner and alert the group by flying away.

Group foraging

Advantages

A group of animals may be better at both finding and capturing food than solitary animals. For species that feed on food that is patchy, the likelihood of locating food is greater if individuals search for food independently and inform the rest of the group when a food patch is found. [12] Information sharing in this way has little cost to the individual who locates the food if it occurs in high abundance in the patch.

Group hunting allows predators to take down larger prey, as well as prey that can outrun the predator but can be caught by an ambush. For example, lionesses (Panthera leo) hunt cooperatively for large prey such as zebra (Equus burchelli) and wildebeest (Connochaetes taurinus), with each lioness adopting particular positions in a formation. [13] The presence of many predators also causes panic in groups of prey, often causing them to flee in different directions making it easier for the predators to single out a target. [1]

Red-billed queleas form huge flocks of thousands of birds Red-billed quelea flocking at waterhole.jpg
Red-billed queleas form huge flocks of thousands of birds

Foraging in a group also has some anti-predator benefits. Being part of a group dilutes an individual's risk of being attacked, as the more group members there are, the lower the probability that that individual will be the victim. [14] Grouping may swamp the predator's capacity to capture prey - for example, hawks are unable to capture more than one yellow-eyed junco per attack. [5] Large groups also cause predator confusion as it makes it difficult for prey to focus on one target. [1] Groups of animals may engage in communal defences, such as mobbing, for further protection. [1]

Disadvantages

Dilution of predation risk only occurs if groups of animals are not more prone to attack than individuals. [1] Often large groups are more conspicuous to predators so grouping may increase the risk of attack. Blue acara cichlid fish (Aequidens pulcher) choose shoals of guppies (Poecilia reticulate) to attack based on how visually conspicuous they are, preferring shoals that are larger or exhibit more movement. [15] Foraging in groups requires sharing so may also lead to greater competition for food.

Effect of group size

Larger groups may have a greater overall vigilance than small groups due to the ‘many eyes’ hypothesis: more eyes scanning for predators means that the proportion of time that at least one individual is vigilant (collective vigilance) is higher. [16] [17] This improved vigilance may allow an individual to decrease the time it allocates to vigilance without any increase in its personal risk of being attacked - particularly as large groups already have a diluted predation risk. [18] Lower individual levels of vigilance with increasing group size has been observed in many bird, mammal and fish species. [7] Individual ostriches (Struthio camelus) and greater rheas (Rhea americana) in large groups both spend less time with their head up than individuals in small groups, however collective vigilance increases with group size in ostriches but not rheas. [17] [19] Therefore, the many eyes hypothesis does not always hold. Although individuals in groups may be able to decrease the time they spend scanning, and hence reach their energy requirements in a shorter period of time, the increased competition for food in groups may mean that animals need to devote more time overall to foraging due to an increased allocation of time for aggressive behaviour during foraging. [18] For example, the rate of fighting between house sparrows (Passer domesticus) increases with the size of the flock. [20]

Alarm signals

Large groups of animals are able to detect predators earlier because of the higher probability that at least one individual is being vigilant when the predator approaches. As many predators rely on the element of surprise in successful attacks, early detection of predators reduces predation risk. [1] The detection of a predator by one individual only translates to collective detection if that individual makes some sort of signal to alert the rest of the group. The signal may be a deliberate call made by the vigilant individual (as in the case of meerkats) or simply the departure of the individual who has detected the predator.

Flocks of birds often exhibit collective detection. One or more birds initially detect the threat, and other birds that did not perceive the threat detect their departure and also respond by fleeing. [7] The departure of multiple birds simultaneously is likely to be a more effective alarm signal than that of a single bird as birds regularly depart flocks for reasons other than predator detection. [7]

Water skaters (Halobates robustus) transmit predator avoidance behaviour to the group through the sense of touch: individuals at the edge of the flotilla detect a predator and move, bumping into their neighbours, who in turn start moving and bumping into more individuals. [21] This ‘wave’ of alarm has been termed the ‘Trafalgar Effect’. [21]

Sentinels

A meerkat (Suricata suricatta) on sentry duty looks out for predators on a perch Suricate, Namibia (2813287155).jpg
A meerkat (Suricata suricatta) on sentry duty looks out for predators on a perch

In some species, individuals in a foraging group take on sentry duty. The sentinels look out for predators (often from a good vantage point) while the rest of the group forages, and sound an alarm when they spot a predator. [1] Sentry duty is particularly important for species whose foraging activity is incompatible with vigilance, or who feed in areas where they are highly exposed to predators. For example, dwarf mongooses (Helogale parvula) dig up arthropods from the ground to eat; an activity which requires fixation of both their vision and olfaction on the prey. [22]

Often, the sentry makes quiet calls that function as a ‘watchman’s song’ to reassure the rest of the group that an individual is on guard. [23] In response to a vocalising sentry, pied babblers (Turdoides bicolor) decrease their own vigilance, spread out further from the group and forage in more exposed patches resulting in a higher intake of biomass. [24]

Guarding may appear to be an altruistic behaviour as an individual on sentry duty is unable to feed, may be more exposed to predators, and may attract the predators attention when they make an alarm call. However meerkats on sentry duty are at no greater risk of predation as they are generally the first to detect predators (e.g. jackals, eagle species) and flee to safety. [25] Meerkats also only go on guard once they are satiated so if no other individual is on sentry duty, guarding may be the most beneficial behaviour as the individual has no requirement for feeding and can benefit from early predator detection. [25]

Cheating

In a large group, it is possible for an individual to cheat by scanning less than other members of the group without having any negative effect on the collective vigilance of the group. Cheating would seem to be the most beneficial strategy as the individual still benefits from the collective detection of the group while being able to feed more than other individuals. However, cheating is not a stable strategy because if all members of the group did it, then there would be no collective vigilance. [26] Adopting a very high level of vigilance in a group is also not a stable strategy as an individual who adopts a lower level of vigilance would have a greater advantage. The evolutionarily stable (ESS) scanning rate is the rate that if all group members adopted, an individual that scanned more or less frequently would have a lower chance of survival. [26]

Maintaining individual vigilance may be a more beneficial strategy if vigilant animals gain some sort of advantage. [27] Non-vigilant individuals are often the last to flee to safety, as groups generally flee in succession from the individual who spots the predator, individuals who were vigilant when the first animal departs, and finally the non-vigilant individuals. [28] Predators may also target less vigilant prey as they are likely to detect the predator later and therefore respond more slowly. Cheetahs (Acinonyx jubatus) select less vigilant Thomson's gazelles (Eudorcas thomsonii) before initiating a chase and target them for attack. [29]

See also

Related Research Articles

<span class="mw-page-title-main">Black-and-white colobus</span> Genus of Old World monkeys

Black-and-white colobuses are Old World monkeys of the genus Colobus, native to Africa. They are closely related to the red colobus monkeys of genus Piliocolobus. There are five species of this monkey, and at least eight subspecies. They are generally found in high-density forests where they forage on leaves, flowers and fruit. Social groups of colobus are diverse, varying from group to group. Resident-egalitarian and allomothering relationships have been observed among the female population. Complex behaviours have also been observed in this species, including greeting rituals and varying group sleeping patterns. Colobi play a significant role in seed dispersal.

<span class="mw-page-title-main">Predation</span> Biological interaction where a predator kills and eats a prey organism

Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation and parasitoidism. It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as seed predators and destructive frugivores are predators.

<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">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">Scaly-breasted munia</span> Species of bird native to South and Southeast Asia

The scaly-breasted munia or spotted munia, known in the pet trade as nutmeg mannikin or spice finch, is a sparrow-sized estrildid finch native to tropical Asia. A species of the genus Lonchura, it was formally described and named by Carl Linnaeus in 1758. Its name is based on the distinct scale-like feather markings on the breast and belly. The adult is brown above and has a dark conical bill. The species has 11 subspecies across its range, which differ slightly in size and color.

<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">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".

<span class="mw-page-title-main">Optimal foraging theory</span> Behavioral ecology model

Optimal foraging theory (OFT) is a behavioral ecology model that helps predict how an animal behaves when searching for food. Although obtaining food provides the animal with energy, searching for and capturing the food require both energy and time. To maximize fitness, an animal adopts a foraging strategy that provides the most benefit (energy) for the lowest cost, maximizing the net energy gained. OFT helps predict the best strategy that an animal can use to achieve this goal.

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.

<span class="mw-page-title-main">Flock (birds)</span>

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">Mobbing (animal behavior)</span> Antipredator adaptation in which individuals of prey species mob a predator

Mobbing in animals is an antipredator adaptation in which individuals of prey 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 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 behavior 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.

The selfish herd theory states that individuals within a population attempt to reduce their predation risk by putting other conspecifics between themselves and predators. A key element in the theory is the domain of danger, the area of ground in which every point is nearer to a particular individual than to any other individual. Such antipredator behavior inevitably results in aggregations. The theory was proposed by W. D. Hamilton in 1971 to explain the gregarious behavior of a variety of animals. It contrasted the popular hypothesis that evolution of such social behavior was based on mutual benefits to the population.

Antipredatory behaviors are actions an animal performs to reduce or rid themselves of the risk of being prey. Many studies have been done on elk to see what their antipredator behaviors consist of.

<span class="mw-page-title-main">Pursuit predation</span>

Pursuit predation is a form of predation in which predators actively give chase to their prey, either solitarily or as a group. It is an alternate predation strategy to ambush predation — pursuit predators rely on superior speed, endurance and/or teamwork to seize the prey, while ambush predators use stealth, luring, the use of surroundings and the element of surprise to capture the prey. While the two patterns of predation are not mutually exclusive, morphological differences in an organism's body plan can create an evolutionary bias favoring either type of predation.

<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

  1. 1 2 3 4 5 6 7 8 9 10 11 Davies, N.B., Krebs, J.R. & West, S.A. (2012) An Introduction to Behavioural Ecology 4th edn, Wiley-Blackwell, Oxford, UK
  2. 1 2 3 Illius, A.W. & Fitzgibbon, C. (1994) Costs of vigilance in foraging ungulates. Animal Behaviour 47: 481-484
  3. 1 2 3 4 Lima, S.L., Valone, T.J. & Caraco, T. (1985) Foraging-efficiency – predation-risk trade-off in the grey squirrel. Animal Behaviour 33: 155-165
  4. 1 2 Brown, J.S. (1999) Vigilance, patch use and habitat selection: foraging under predation risk. Evolutionary Ecology Research 1: 49-71
  5. 1 2 Caraco, T., Martindale, S. & Pulliam, H.R. (1980) Avian flocking in the presence of a predator. Nature 285: 400-401
  6. 1 2 3 Milinski, M. & Heller, R. (1978) Influence of a predator on the optimal foraging behaviour of sticklebacks (Gasterosteus aculeatus). Nature 275: 642-644
  7. 1 2 3 4 Lima, S.L. (1995) Back to the basics of anti-predatory vigilance: the group-size effect. Animal Behaviour 49: 11-20
  8. 1 2 3 Gilliam, J.F. (1982) Foraging under mortality risk in size-structured populations. PhD thesis. Michigan State University, MI
  9. ↑ Clarke, J.A. (1983) Moonlight’s influence on predator/prey interactions between short-eyed owls (Asio flammeus) and deermice (Peromyscus maniculatus). Behavioral Ecology and Sociobiology 13: 205-209
  10. ↑ Makowska, J. & Kramer, D.L. (2007) Vigilance during food handling in grey squirrels, Sciurus carolinensis. Animal Behaviour 74: 153-158
  11. 1 2 3 Lima, S.L. (1988) Vigilance and diet selection: a simple example in the dark-eyed junco. Canadian Journal of Zoology 66: 593-596
  12. ↑ Clark, C.W. & Mangel, M. (1984) Foraging and flocking strategies: information in an uncertain environment. The American Naturalist 123(5): 626-641
  13. ↑ Stander, P.E. (1992) Cooperative hunting in lions: the role of the individual. Behavioral Ecology and Sociobiology 29: 445-454
  14. ↑ Foster, W.A. & Treherne, J.E. (1981) Evidence for the dilution effect in the selfish herd from fish predation on a marine insect. Nature 293: 466-467
  15. ↑ Krause, J. & Godin, J.J. (1995) Predator preferences for attacking particular prey group sizes: consequences for predator hunting success and prey predation risk. Animal Behaviour 50: 465-473
  16. ↑ Lima, S.L. & Dill, L.M. (1990) Behavioral decisions made under the risk of predation: a review and prospectus. Canadian Journal of Zoology 68: 619-640
  17. 1 2 Fernandez, G.J., Capurro, A.F. & Reboreda, J.C. (2003) Effect of group size on individual and collective vigilance in greater rheas. Ethology 109: 413-425
  18. 1 2 Roberts, G. (1996) Why individual vigilance declines as group size increases. Animal Behaviour 51: 1077-086
  19. ↑ Bertram, B.C.R. (1980) Vigilance and group size in ostriches. Animal Behaviour 28: 278-286
  20. ↑ Barnard, C.J. (1980) Factors affecting flock size mean and variance in a winter population of house sparrows (Passer domesticus L.) Behaviour 74(1):114-127
  21. 1 2 Treherne, J.E. & Foster, W.A. (1981) Group transmission of predator avoidance behaviour in a marine insect: the Trafalgar Effect. Animal Behaviour 29: 911-917
  22. ↑ Rasa, O.A.E. (1986) Coordinated vigilance in dwarf mongoose family groups: the ‘Watchman’s Song’ hypothesis and the costs of guarding. Ethology 71: 340-344
  23. ↑ Wickler, W. (1985) Coordination of vigilance in bird groups, the ‘Watchman’s Song’ hypothesis. Zeitschrift fur Tierphysiologie, Tierernahrung und Futtermittelkunde 69: 250-253
  24. ↑ Hollen, L.I., Bell, M.B.V. & Radford, A.N. (2008) Cooperative sentinel calling? Foragers gain increased biomass intake. Current Biology 18: 576-579
  25. 1 2 Clutton-Brock, T.H., O’Riain, M.J., Brotherton, P.N.M., Gaynor, D., Kansky, R., Griffin, A.S. & Manser, M. (1999) Selfish sentinels in cooperative mammals. Science 284: 1640-1644
  26. 1 2 Pulliam, H.R. (1982) The scanning behavior of juncos: a game-theoretical approach. Journal of Theoretical Biology 95: 89-103
  27. ↑ McNamara, J.M. & Houston, A.I. (1992) Evolutionarily stable levels of vigilance as a function of group size. Animal Behaviour 43: 641-658
  28. ↑ Lima, S.L. (1994) On the personal benefits of anti-predatory vigilance. Animal Behaviour 48: 734-736
  29. ↑ Fitzgibbon, C.D. (1989) A cost to individuals with reduced vigilance in groups of Thomson’s gazelles hunted by cheetahs. Animal Behaviour 37(3): 508-510
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.