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 they were not strongly influenced by flocking, feeding and search behaviour of grackle was strongly affected by the sex of the grackles, the season, and the local feeding area, and grackle feeding behaviour seemed less closely adjusted to flocking than to other environmental factors.
Abstract: Feeding rates, search paths, and surveillance behaviour of great-tailed grackles were measured to test the hypotheses that flocking influences: (a) feeding rates, (b) search behaviour, and (c) predator detection.Peck rates of grackles feeding on open grass meadows in Gatun, Panama Canal Zone, did not vary with flock density and variation in peck rates was also independent of density. When grackles were in denser flocks, their search paths were straighter and, during the wet season only, they moved slower in denser flocks. Female grackles in denser flocks paused less often to scan the surrounding environment, presumably for potential danger.Although they were not strongly influenced by flocking, feeding and search behaviour of grackles was strongly affected by the sex of the grackles, the season, and the local feeding area. Grackle feeding behaviour hence seemed less closely adjusted to flocking than to other environmental factors.
28 citations
TL;DR: The motivation for the mathematical solution of the following general search problem is defense against missiles, early detection is crucial, and an asymptotically optimum search procedure is obtained.
Abstract: In defense against missiles, early detection is crucial. This is the motivation for the mathematical solution of the following general search problem. Objects arrive in accordance with a Poisson process. Having arrived, the object appears (and remains until detected) in box i with probability pi. A single scan of box i costs Ci (possibly including the cost of false alarms), takes time ti, and, if the object is present in box i at the beginning of the scan, will detect it with probability Pi. The resultant gain gi(t) is a nonincreasing function of t, the delay between arrival and the beginning of the detecting look, i = 1, 2, …, n. An asymptotically optimum search procedure is obtained. A number of particular cases of interest are solved.
20 citations
TL;DR: The test of operational meaningfulness is applied to the many detection laws that have been formulated and used in the mathematical optimization of search, and given as generalizations of those first developed in the United States Navy during and immediately following World War II.
Abstract: This paper applies the test of operational meaningfulness to the many detection laws that have been formulated and used in the mathematical optimization of search, and given as generalizations of those first developed in the United States Navy during and immediately following World War II. The word "operational" is used both in the sense of practical O.R. and in that of P. W. Bridgman's well-known requirement: that in applying mathematics to the material world, the physical preconditions implied in the quantities used, the operations for measuring them, and their laws of consistency must be set forth explicitly. It is submitted that this criterion will orient O.R. work toward useful developments in the search theory and may serve to identify as such those theories that are of chief interest as developments in pure mathematics. Finally, we note that the requirement that every numerical assumption of probability distributions in a study of the outside world must be based on objective evidence is perfectly consistent with the "subjective" conception of probability, viz., that its meaning is apprehended intuitively-the former measures what the latter defines.
17 citations