Vigilance Behaviour in Grazing African Antelopes
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.
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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
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
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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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
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
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TL;DR: Although links do exist between ecology and behavior, they nevertheless represent distinct realms of natural selection in which social behavior appears as the more conservative element, and the theoretical basis for this is discussed.
Abstract: Much of the social behavior and organization of ungulates can be related to ecological parameters such as fiber content of forage, plant productivity, plant biomass, plant species diversity, productivity gradients, temporal and spatial fluctuations in productivity, habitat stability, food dispersion, three-dimensional structure of habitat, colonization, and predator density and diversity. These ecological variables can be linked via individual natural selection with the species' anti-predator strategies, emphasis on different channels of communication, relative frequency of damaging and non-damaging overt aggression, gregariousness and group structure, juvenile dispersal, home-range traditions, monogamy and polygamy, sexual dimorphism, territoriality, hierarchical rank structure, and plasticity of social structures. The ecological variables have primary manifestations which are behavior or which affect behavior, as well as secondary manifestations affecting behavior. There are logical links between the hypothesis linking ecology and behavior discussed here with some principles from bioenergetics, zoogeography, and paleontology. Although links do exist between ecology and behavior, they nevertheless represent distinct realms of natural selection in which social behavior appears as the more conservative element. The theoretical basis for this is discussed.
460 citations
"Vigilance Behaviour in Grazing Afri..." refers background in this paper
...Such habitat differences may have influenced the evolution of social and anti-predator behaviour in antelope (GEIST, 1974; JARMAN, 1974; ESTES, 1974) and may also affect both predator and prey behaviour on a day to day basis (SCHALLER, 1972; KRUUK, 1972; CURIO, 1976; EDMUNDS, 1974)....
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...If scanning reduces predation, it may take up less of the large animals' time either because both the number and the range of potential predators are smaller (JARMAN, 1974; GEIST, 1974), or because these antelope, being found in large groups, either are (a) less easy for a predator to find, (b) share vigilance with other group members (CARACAO et al....
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TL;DR: In this paper, the authors observed wild ostriches while feeding alone or in groups of up to four birds, and their vigilance (proportion of time with the head up) recorded.
387 citations
TL;DR: The risk of predation was apparently higher in the fields where birds scanned more frequently than in the cattlesheds and where scanning was negatively influenced by flock size but positively influenced by distance from cover.
332 citations
"Vigilance Behaviour in Grazing Afri..." refers background in this paper
...sively, most recently by BERTRAM (1980), BARNARD (1980), CARACAO et al....
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...PULLIAM, 1973; LAZARUS, 1972; KENWARD, 1978; TREISMAN 1975a, b; BERTRAM, 1980) and the location of food, either directly (KREBS & PARTRIDGE, 1973; BARNARD, 1980) or indirectly, by the behaviour of other group members (e....
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...Birds are known to change their vigilance behaviour very flexibly in response to changes in the risk of predation: for example, BARNARD (1980) showed that house sparrow, Passer domesticus, flocks were much more vigilant when in open habitats which exposed them to possible predation from the air than when they were in barns and apparently less vulnerable....
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