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: Levels of vigilance of an individual rabbit during feeding decreased with proximity to that rabbit's ‘consort’, and rabbits increased their vigilance in the presence of greater numbers of non-consort rabbits either nearby or over 12 m away.
68 citations
TL;DR: It is suggested that, since pure grazers' foraging is limited to a fairly continuously distributed food supply, their foraging consists mainly of teasing out and biting off grass leaves and the organization of theirForaging behaviour is determined by the structure and quality of the grass sward.
Abstract: The second to second organization of the foraging behaviour of eleven species of African ungulates is described, with particular emphasis on locomotion while foraging and on the time spent feeding. It was predicted that foraging behaviour should change with the species' body size and stomach specialization and, within a species, with the seasonal or spatial changes in the quality and availability of the food supply. A feeding site was defined as the area which a feeding animal could reach without moving either of its forefeet. Feeding subjects thus encountered a new site every time they took a step with either forefoot and foraging behaviour could be described in terms of the organization of a series of behavioural events (steps) and bouts of activity (feeding). Five indices were used to summarize all records obtained. Only one of these, the proportion of time spent feeding, was significantly correlated with the species' body size. The other four indices include: the rate of movement (in steps per second), the mean feeding time per step, the proportion of sites encountered which carried at least some acceptable food, and the mean time spent feeding from those accepted sites. These last four indices were apparently more strongly affected by the species' stomach specialization than by its body size. The five species with the largest sample sizes (reedbuck, impala, tsessebe, wildebeeste, buffalo) were used to investigate the tendency found within all study species for foraging behaviour to vary seasonally. Firstly, both the mean feeding time per step and the mean feeding time per accepted site were found to be positively correlated with indicators of vegetation bulk and maturity, but negatively correlated with an index of fresh green growth, for all five species: it is suggested that this is due to changes in both the amount of food taken from a given site and in the time needed to ingest a given bulk of food. Secondly, the organization of events within foraging sessions (described in terms of the frequency distributions of step intervals, feeding durations, and the lengths of runs of acceptance or rejection of feeding sites) varied through the year: in particular, food patch size, indicated by the length of sequences of accepted sites, was apparently largest just before the end of the rains, when the vegetation should have been most uniform in quality. Thirdly, the reedbuck is a specialist grazer which, because of its body size, might be expected to feed very selectively within the grass layer: the feeding behaviours of the other four species most closely resembled that of the reedbuck when these four species were feeding off long grass in the dry season, conditions which presented them with much low quality food senescent grass hampering access to very small amounts of higher quality green matter. It is suggested that, as in domestic ungulates, feeding behaviour varies within a species with the proportion of low fibre, high protein, green growth in the vegetation, and in the contrast in quality between the various plant parts. A multivariate analysis was used to identify the foraging characteristics of individual ruminant species. Species which were specialist grass feeders (bulk/roughage feeders) encountered more sites more predictably, and spent more time feeding off those sites, than did species which were known to switch from grasses to other food sources to take advantage of changes in the relative quantity and abundance of food types in the habitat (intermediate feeders). It is suggested that, since pure grazers' foraging is limited to a fairly continuously distributed food supply, their foraging consists mainly of teasing out and biting off grass leaves and the organization of their foraging behaviour is determined by the structure and quality of the grass sward. Intermediate feeders, on the other hand, had the option of taking higher quality but less continuously distributed items, such as fruits, and their foraging may have involved seeking out and moving between such items. Pure grazers' foraging behaviour is thus seen as being dominated by food capture and handling events, while intermediate feeders may be more strongly influenced by food search or pursuit requirements. It is likely that grazers differed from intermediate feeders not only in the basic organization of their foraging behaviour, but also in the way that this organization was affected by the species' body size.
67 citations
TL;DR: These findings suggest that individuals in groups experience a trade-off between predation-related benefits and costs arising from feeding competition, and Habitat structure and forage likely influence the nature of this trade-offs; thus, variation in these ecological factors may maintain variation in group size.
Abstract: The main ecological factors that are hypothesized to explain the striking variation in the size of social groups among large herbivores are habitat structure, predation, and forage abundance and distribution; however, their relative roles in wild populations are not well understood I combined analyses of ecological correlates of spatial variation in group size with analyses of individual behaviour in groups of different sizes to investigate factors maintaining variation in group size in an Indian antelope, the blackbuck Antilope cervicapra I measured group size, habitat structure, forage, and the occurrence of predators in ten blackbuck populations, and, at a smaller spatial scale, within an intensively studied population To examine the processes by which these ecological factors influence group size, I used behavioural observations and an experiment to estimate the shape of the relationship between group size and potential costs and benefits to individuals Group size varied extensively both among and within populations Analyses of spatial variation in group size suggested that both forage and habitat structure influence group size: large-scale, among-population variation in group size was primarily related to habitat structure, while small-scale, within-population variation was most closely related to forage abundance Analyses of individual behaviour suggested that larger groups incur greater travel costs while foraging However, individuals in larger groups appeared to experience greater benefits, namely the earlier detection of a "predator", a reduction in vigilance, and an increase in the time spent feeding Overall, these findings suggest that individuals in groups experience a trade-off between predation-related benefits and costs arising from feeding competition Habitat structure and forage likely influence the nature of this trade-off; thus, variation in these ecological factors may maintain variation in group size The role of predation pressure and other factors in explaining the remaining variation needs further exploration
67 citations
Cites background from "Vigilance Behaviour in Grazing Afri..."
...Individuals in groups may also experience benefits related to reduced predation, such as spending less time being vigilant and more time feeding compared with solitary animals (Underwood 1982; Blumstein and Daniel 2002)....
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TL;DR: Results are what would be expected if grooming serves to remove ticks before they can attach and engorge, and supports the view that grooming is an evolved response to the threat of excessive tick burden in the impala's natural environment.
66 citations
Cites background from "Vigilance Behaviour in Grazing Afri..."
...In a previous study at Kyle, impala in smaller groups engaged in more ‘head-up’ vigilance behaviour than those in larger groups (Underwood 1982)....
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TL;DR: The relationship between group size and vigilance rate was investigated in Cazorla and Segura (South-eastern Spain) as mentioned in this paper, where adults of both sexes were more vigilant than juveniles and more vigilance occurred in the morning than in the afternoon and evening combined.
Abstract: and Summary
Observation of ibex (Capra pyrenaica) in Cazorla and Segura (South-eastern Spain) revealed a negative relationship when group size was plotted against individual time dedicated to vigilance and a positive one when plotted against time used for feeding. Generally, adults of both sexes were more vigilant than juveniles and more vigilance occurred in the morning than in the afternoon and evening combined. Peripheral animals were more vigilant than central ones.
The relationship between group size and vigilance rate shows that when mixed groups become large, and correspondingly when the level of interactions is frequent, the negative relationship observed between small group size and rate of vigilance is broken. This occurs during the rut, when the importance of the animals as look-out also decreases if they are located at the periphery of the group, due to an increase in the interest in activities related to reproduction.
Zusammenfassung
Beim Iberiensteinbock in Sudostspanien nimmt mit der Truppgrose die Wachsamkeit der Individuen ab, ihre Fresdauer zu. Erwachsene beiderlei Geschlechts sind wachsamer als Junge, und alle sind morgens langer wachsam als nachmittags und abends. Individuen am Gruppenrand sind wachsamer als die im Gruppenzentrum.
In ganz grosen gemischten Gruppen wahrend der Paarungszeit folgt die Wachsamkeit diesen Regeln nicht. Dann ist die Aufmerksamkeit mehr auf die vielen Interaktionen in der Gruppe gerichtet.
63 citations
References
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TL;DR: Seven major types of sampling for observational studies of social behavior have been found in the literature and the major strengths and weaknesses of each method are pointed out.
Abstract: Seven major types of sampling for observational studies of social behavior have been found in the literature. These methods differ considerably in their suitability for providing unbiased data of various kinds. Below is a summary of the major recommended uses of each technique: In this paper, I have tried to point out the major strengths and weaknesses of each sampling method. Some methods are intrinsically biased with respect to many variables, others to fewer. In choosing a sampling method the main question is whether the procedure results in a biased sample of the variables under study. A method can produce a biased sample directly, as a result of intrinsic bias with respect to a study variable, or secondarily due to some degree of dependence (correlation) between the study variable and a directly-biased variable. In order to choose a sampling technique, the observer needs to consider carefully the characteristics of behavior and social interactions that are relevant to the study population and the research questions at hand. In most studies one will not have adequate empirical knowledge of the dependencies between relevant variables. Under the circumstances, the observer should avoid intrinsic biases to whatever extent possible, in particular those that direcly affect the variables under study. Finally, it will often be possible to use more than one sampling method in a study. Such samples can be taken successively or, under favorable conditions, even concurrently. For example, we have found it possible to take Instantaneous Samples of the identities and distances of nearest neighbors of a focal individual at five or ten minute intervals during Focal-Animal (behavior) Samples on that individual. Often during Focal-Animal Sampling one can also record All Occurrences of Some Behaviors, for the whole social group, for categories of conspicuous behavior, such as predation, intergroup contact, drinking, and so on. The extent to which concurrent multiple sampling is feasible will depend very much on the behavior categories and rate of occurrence, the observational conditions, etc. Where feasible, such multiple sampling can greatly aid in the efficient use of research time.
12,470 citations
TL;DR: An antithesis to the view that gregarious behaviour is evolved through benefits to the population or species is presented, and simply defined models are used to show that even in non-gregarious species selection is likely to favour individuals who stay close to others.
3,343 citations
Additional excerpts
...The 'selfish herd' (HAMILTON, 1971)...
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TL;DR: The paper describes different feeding styles among antelope, in terms of selection of food items and coverage of home ranges, and argues that these feeding styles bear a relationship to maximum group size of feeding animals through the influence of dispersion ofFood items upon group cohesion.
Abstract: The types of social organisation displayed by the African antelope species have been assigned in this paper to five classes, distinguished largely by the strategies used by the reproductively active males in securing mating rights, and the effects of those strategies on other social castes. The paper attempts to show that these strategies are appropriate to each class because of the effects of other, ecological, aspects of their ways of life. The paper describes different feeding styles among antelope, in terms of selection of food items and coverage of home ranges. It argues that these feeding styles bear a relationship to maximum group size of feeding animals through the influence of dispersion of food items upon group cohesion. The feeding styles also bear a relationship to body size and to habitat choice, both of which influence the antelope species' antipredator behaviour. Thus feeding style is related to anti-predator behaviour which, in many species, influences minimum group size. Group size and the pattern of movement over the annual home range affect the likelihood of females being found in a given place at a given time, and it is this likelihood which, to a large extent, determines the kind of strategy a male must employ to achieve mating rights. The effects of the different strategies employed by males can be seen in such aspects of each species' biology as sexual dimorphism, adult sex ratio, and differential distribution of the sexes.
2,088 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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...The smaller and, according to JARMAN (1974), the more selective species are those which show significant correlations between the rate of looking and indices of feeding success, supporting the possibility that scanning forms a part of foraging behaviour....
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1,193 citations
Book•
21 Sep 1976
TL;DR: This chapter discusses hunting for Prey, the Diversity of Hunting Methods, and the Motivation Underlying Feeding Responses of Predator-Prey Interactions.
Abstract: 1 Internal Factors.- A. Hunger: Expression through Overt behavior.- I. Predatory Schedules.- 1. Patterns of Satiation.- 2. Feast and Famine.- II. Hunger and Diel Rhythms.- III. The Ramification of Hunger Effects.- 1. Capture-eliciting Prey Stimuli.- 2. Search behavior.- IV. The Motivation Underlying Feeding Responses.- 1. Hunger Thresholds of Feeding Response Components.- 2. The Complexity of Predatory Motivation.- V. The Diversity of Foraging Tactics.- VI. Feeding Components Affected and not Affected by Hunger.- B. The Control of Feeding Responses by Factors Other than Hunger.- I. The Readiness to Hunt.- II. Prey Storing.- III. Providing Food for Dependent Family Members.- C. The Problem of Specific Hungers.- I. Switching of Prey.- II. The Prey-density Predation Curve.- III. Swamping the Appetite of Predators.- D. Daily and Annual Rhythms in Predator-Prey Interactions.- I. Daily Rhythm of Predation.- II. Daily Activity Patterns of the Prey.- III. Annual Rhythm of Predation.- 2 Searching for Prey.- A. Path of Searching and Scanning Movements.- B. Area-concentrated Search.- I. Short-term Area Concentration.- 1. Living Scattered and Area-concentrated Search.- 2. The Nature of the Path Changes.- 3. Search Behavior after the Disappearance of Prey.- II. Long-term Area Concentration.- III. One-prey : One-place Association.- C. Object-concentrated Search.- I. Existence and Properties of "Searching Image".- 1. Ecological Evidence.- 2. Experimental Evidence.- II. Social Facilitation of Searching Image Formation.- III. Searching Image and "Training Bias".- IV. Searching Image and Profitability of Hunting.- 1. Ecological Evidence for Profitability of Hunting.- 2. Experimental Evidence for Profitability of Hunting.- V. Prey-specific Expectation.- VI. Ecological Implications of Searching Image.- 3 Prey Recognition.- A. The Stimulus-specificity of Prey Capture.- I. Capture-eliciting Prey Stimuli.- II. Capture-inhibiting Prey Stimuli.- B. One-prey : One-response Relationships.- C. The Assessment of the Circumstances of a Hunt.- D. Prey Recognition by Prey-related Signals.- E. Prey Stimulus Summation.- F. Novelty Versus Familiarity.- I. The Rejection of Novel Prey.- II. Familiarization with Prey and Its Consequences.- G. The Multi-channel Hypothesis of Prey Recognition.- 4 Prey Selection.- A. Preying upon the Weak and the Sick.- B. Preying upon the Odd and the Conspicuous.- C. The Mechanics of Prey Selection.- D. Evolutionary Implications.- 5 Hunting for Prey.- A. Modes of Hunting.- I. Hunting by Speculation.- II. Stalking and Ambushing.- 1. Stalking.- 2. Ambushing.- III. Prey Attack under Disguise.- IV. Pursuit of the Prey.- 1. Changes of Velocity of Attack (Pursuit).- 2. Interception of the Flight Path.- 3. Counteradaptations of the Prey.- V. Exhausting Dangerous Prey.- VI. Insinuation.- VII. Scavenging and Cleptoparasitism.- 1. Modes and Extent.- 2. Cleptoparasitism and Competition.- 3. Counter-measures of the Robbed.- VIII. Tool-use.- IX. Mutilation.- B. The Diversity of Hunting Methods.- I. Prey-specific Methods.- II. Situation-specific Methods.- III. Mechanisms and Causes of Predatory Versatility.- 1. General.- 2. Individual Predatory Repertories.- 3. The Persistence of Individual Traits.- 4. Predatory Specialization and Structural Modification.- 5. Predatory Versatility in Relation to Prey Availability.- C. Behavioral Aspects of Hunting Success.- I. A Comparison of Hunting Success across Predator Species.- II. Variables Influencing Hunting Success within Predator Species.- III. Aspects of Communal Hunting.- 1. Modes and Properties of Communal Hunting.- 2. Factors Conducive to Communal Hunting.- 3. Benefits of Communal Hunting.- References.- Scientific Names of Animals and Plants.
919 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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