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Journal ArticleDOI

Vigilance Behaviour in Grazing African Antelopes

01 Jan 1982-Behaviour (Brill)-Vol. 79, Iss: 2, pp 81-107
TL;DR: Time spent looking varied with position within the group; this effect was strongest in closed habitats, where central animals tended to scan least and feed most, and within species, animals inclosed habitats, those with dense vegetation, tended to spend more time in looking than did animals in the open.
Abstract: African antelope may devote a large proportion of their foraging time to looking around. The factors affecting such vigilance behaviour are examined for grazing antelope, five species being studied in detail. The proportion of time spent looking decreased as species body weight increased. Within species, animals in closed habitats, those with dense vegetation, tended to spend more time in looking than did animals in the open. There was some evidence that vigilance, presumably for predators, was shared by group members, but in one species, impala, vigilance apparently increased with group size and with proximity to neighbours. Time spent looking varied with position within the group; this effect was strongest in closed habitats, where central animals tended to scan least and feed most. Vigilance increased as feeding success decreased, partly due to mutual interference between looking and feeding. The possible social, foraging and predator-detection values of vigilance are discussed. A simple model is introduced to help explain the effects of cover and to facilitate further discussion.
Citations
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Journal ArticleDOI
TL;DR: This work has shown that predation is a major selective force in the evolution of several morphological and behavioral characteristics of animals and the importance of predation during evolutionary time has been underestimated.
Abstract: Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary ti...

7,461 citations

Journal ArticleDOI
TL;DR: Most of the studies fail to adequately demonstrate an unambiguous relationship between vigilance behaviour and group size, but many studies reveal interesting features of the relationship between Vigilance and Group size that should provide fruitful avenues for future research.
Abstract: One commonly cited benefit to animals that forage in groups is an increase in the probability of detecting a predator, and a decrease in the time spent in predator detection. A mathematical model (Pulliam 1973) predicts a negative relationship between group size and vigilance rates. Over fifty studies of birds and mammals report that the relationship at least partly explains why individuals forage in groups. This review evaluates the strength of these conclusions based on their evidence. Those variables that may confound the relationship between vigilance and group size are outlined, and their control is assessed for each study. The variables I consider to be important include the density and type of food; competition between individuals; the proximity to both a safe place and the observer; the presence of predators; the visibility within the habitat; the composition of the group; the ambient temperature and the time of day. Based on these assessments, most of the studies fail to adequately demonstrate an unambiguous relationship between vigilance behavior and group size. Nevertheless, many studies reveal interesting features of the relationship between vigilance and group size that should provide fruitful avenues for future research.

1,051 citations

Journal ArticleDOI
TL;DR: Male elk and bison showed no response to the reintroduction of wolves, maintaining the lowest levels of vigilance throughout the study (12 and 7% of the time was spent vigilant, respectively).
Abstract: The elk or wapiti (Cervus elaphus) and bison (Bison bison) of Yellowstone National Park have lived in an environment free of wolves (Canis lupus) for the last 50 years. In the winter of 1994-1995, wolves were reintroduced into parts of Yellowstone National Park. Foraging theory predicts that elk and bison would respond to this threat by increasing their vigilance levels. We tested this prediction by comparing vigilance levels of elk and bison in areas with wolves with those of elk still in "wolf-free" zones of the Park. Male elk and bison showed no response to the reintroduction of wolves, maintaining the lowest levels of vigilance throughout the study (12 and 7% of the time was spent vigilant, respectively). Female elk and bison showed significantly higher vigilance levels in areas with wolves than in areas without wolves. The highest vigilance level (47.5 ± 4.1%; mean ± SE) was seen by the second year for female elk with calves in the areas with wolves and was maintained during the subsequent 3 years of...

915 citations


Cites background from "Vigilance Behaviour in Grazing Afri..."

  • ...Indeed, various authors (Underwood 1982; Lagory 1986; Scheel 1993; Bednekoff and Ritter 1994; Molvar and Bowyer 1994) have shown this to be the case for a variety of ungulate species....

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Journal ArticleDOI
TL;DR: Simulations based on the energy-intake model suggest a number of key environmental factors that should determine the impact of forage maturation and spatial variation on herbivore distribution patterns.
Abstract: Three general hypotheses have been proposed to explain why many large herbivores have highly aggregated patterns of distribution: dilution of predation risk, maintenance of forage in an immature bu...

437 citations

Journal ArticleDOI
TL;DR: A simple model shows that maximal energetic efficiency is associated with immediate consumption, whereas (under the field conditions studied) carrying items to the safety of trees provides for minimal exposure to predation.

372 citations

References
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Journal ArticleDOI
05 Jun 1980-Nature
TL;DR: A trained hawk was flown over flocks of granivorous yellow-eyed juncos to compare time budgets in the presence and absence of a predator, and it was found that time budgets changed after the predator was introduced and also that flock size increased in the absence of the predator.
Abstract: Although there are several possible advantages of flocking1–3, many authors suggest that birds forage in groups to reduce the risk of predation (see citations in ref. 4). One version of the ‘many eyes’ hypothesis proposes that flocking allows individuals to spend less time scanning for predators and more time feeding5,6. However, flocking may also cause individuals to lose time and energy in fighting one another. The way a bird divides its time among these activities, its time budget, may depend on variables governing foraging requirements and the chance of predation7. As one such variable is the frequency of attacks by predators8, we flew a trained hawk over flocks of granivorous yellow-eyed juncos (Junco phaeonotus) to compare time budgets in the presence and absence of a predator. We found that time budgets changed after the predator was introduced and also that flock size increased in the presence of the predator.

329 citations

Journal ArticleDOI
Ian Vine1
TL;DR: A model to account for cases where the predator emerges in the midst of an aggregation of potential prey, and indicates that the most probable dispersion is a tight circular flock of all the prey animals in the vicinity.

264 citations

Journal ArticleDOI
TL;DR: The contribution of predation to the evolution of gregariousness is examined, and it is suggested that the needs of both predator and prey to conceal themselves and to detect the other may have been a major factor directing the development of social behaviour.

251 citations

Journal ArticleDOI
TL;DR: These results are compatible with L. Tinbergen's hypothesis that birds may use ‘searching images’, but it is argued that this term itself is unhelpful.

205 citations

Journal ArticleDOI
TL;DR: The capture of prey by the African lion in Ngorongoro Crater, Tanzania, is examined and success in stalking appears to depend primarily upon the failure of the prey to see the approaching lion until it is within its effective distance.
Abstract: The capture of prey by the African lion in Ngorongoro Crater, Tanzania, is examined. For analytic purposes the process is envisaged as a consecutive set of events: searching, stalking, attacking, a...

181 citations