Variation In Vigilance Research Articles

Functions of vigilance behaviour in a social carnivore, the spotted hyaena, Crocuta crocuta

Risk is a fundamental driver of prey behaviour, but the importance of risk in the decision-making processes of top predators is poorly understood. We investigated the functions of vigilance behaviour in wild spotted hyaenas. These large carnivores have few predators but face frequent threats of attack and food theft by conspecifics. We made repeated observations of vigilance behaviour by hyaenas when they were resting, feeding and nursing, and examined variation due to age, group size, social rank, and factors related to predation risk. We used these observations to test whether vigilance functions in hyaenas to detect prey, mates, conspecific threats or interspecific threats, and whether functions differ between juveniles and adults. We found that adults were more vigilant than juveniles in all contexts. Vigilance by adults was greatest when nursing, but nursing females reduced their vigilance as cubs matured. Among both age groups, vigilance decreased with increasing group size, and hyaenas were less vigilant when feeding on high-quality food than when feeding on low-quality food. Social rank did not affect vigilance in either age group. Individual adults, but not juveniles, showed consistent patterns of vigilance within, but not between, behavioural contexts. Surprisingly, our results indicate that the primary function of vigilance in hyaenas is to detect interspecific threats. Furthermore, vigilance was context specific, and adult hyaenas showed individual variation in vigilance within behavioural contexts. These findings illustrate the relative importance of particular risks in shaping vigilance behaviour of a top carnivore.

Heritability of anti‐predatory traits: vigilance and locomotor performance in marmots

Animals must allocate some proportion of their time to detecting predators. In birds and mammals, such anti-predator vigilance has been well studied, and we know that it may be influenced by a variety of intrinsic and extrinsic factors. Despite hundreds of studies focusing on vigilance and suggestions that there are individual differences in vigilance, there have been no prior studies examining its heritability in the field. Here, we present one of the first reports of (additive) genetic variation in vigilance. Using a restricted maximum likelihood procedure, we found that, in yellow-bellied marmots (Marmota flaviventris), the heritability of locomotor ability (h(2)=0.21), and especially vigilance (h(2) = 0.08), is low. These modest heritability estimates suggest great environmental variation or a history of directional selection eliminating genetic variation in these traits. We also found a significant phenotypic (r(P) = -0.09 +/- 0.04, P = 0.024) and a substantial, but not significant, genetic correlation (r(A) = -0.57 +/- 0.28, P = 0.082) between the two traits (slower animals are less vigilant while foraging). We found no evidence of differential survival or longevity associated with particular phenotypes of either trait. The genetic correlation may persist because of environmental heterogeneity and genotype-by-environment interactions maintaining the correlation, or because there are two ways to solve the problem of foraging in exposed areas: be very vigilant and rely on early detection coupled with speed to escape, or reduce vigilance to minimize time spent in an exposed location. Both strategies seem to be equally successful, and this 'locomotor ability-wariness' syndrome may therefore allow slow animals to compensate behaviourally for their impaired locomotor ability.

A comparative analysis of vigilance in birds

Individual variation in vigilance is known to vary with factors such as group size but the ecological determinants of vigilance among species have not been examined thus far in a systematic fashion. Earlier analyses suggested that vigilance should be lower in larger species and in species living in larger groups. These analyses were based on a small number of species and failed to take into account phylogenetic relationships among species. Here, I examined ecological determinants of vigilance in a large sample of bird species using a phylogenetic framework. I focused on vigilance in foraging groups of birds in the non-breeding season. Among species, vigilance by solitary foragers was not influenced by body mass. However, among species, asymptotic vigilance, the plateau reached by vigilance in larger groups, decreased with increasing group size in vegetarian clades but not in carnivorous clades. Asymptotic vigilance also increased with increasing body mass in vegetarian clades but not in carnivorous clades. Increasing group size may allow species to reduce vigilance in response to decreased predation risk. Increasing body mass may allow species to increase vigilance because more non-foraging time is available in larger species. Diet may modulate the effect of body mass and group size through factors such as within-group vigilance or foraging techniques.

What is the magnitude of the group-size effect on vigilance?

Vigilance has been predicted to decrease with group size due to increased predator detection and dilution of predation risk in larger groups. Although earlier literature reviews have provided ample support for this prediction, an increasing number of studies have failed to document a decline in vigilance with group size. In addition, support for this prediction has been based thus far on the P value of the relationship between vigilance and group size rather than on a quantitative assessment of effect magnitude. Here, I use a meta-analysis of empirical relationships between vigilance and group size in birds published in the last 35 years to provide a reassessment of the group-size effect on vigilance. Nearly one-third of all published relationships between vigilance and group size were not significant (n = 172). Results from the meta-analysis indicate weak to moderate negative correlations between group size and time spent vigilant (n = 43), scan frequency (n = 29), or scan duration (n = 20). The magnitude of the relationship was stronger in studies that controlled the amount of food available to birds. A funnel plot of the relationship between correlation coefficients and sample size failed to reveal an obvious publication bias. Although the meta-analysis results generally support the prediction that vigilance should decline with group size, a large amount of variation in vigilance remains unexplained in avian studies.

Variation in Vigilance in White-tailed Deer (Odocoileus Virginianus) in Northeastern Kansas

This study was designed to test hypotheses regarding vigilance (a state of alertness that allows an animal to detect the presence of predators or other threats) in white-tailed deer (Odocoileus virginianus). Based on findings on other species, we predicted that: (1) increasing group size would result in decreased individual vigilance; (2) juveniles would be less vigilant than adults; and (3) males would be less vigilant than females. Deer were observed from a tower in northeastern Kansas from May through Jul. 2001 at dawn and dusk. In accordance with other species, individual vigilance was negatively correlated with group size and juveniles spent less time vigilant than adults. However, there was no apparent difference in vigilance levels between the sexes in adults. We conclude that deer exploit loose aggregations to maximize foraging time by decreasing individual vigilance (without increasing risk) and that the trade off between vigilance and foraging intensity changes with maturation.

Vigilance and fitness in grey partridges Perdix perdix: the effects of group size and foraging‐vigilance trade‐offs on predation mortality

1. Vigilance increases fitness by improving predator detection but at the expense of increasing starvation risk. We related variation in vigilance among 122 radio-tagged overwintering grey partridges Perdix perdix (L.) across 20 independent farmland sites in England to predation risk (sparrowhawk Accipiter nisus L., kill rate), use of alternative antipredation behaviours (grouping and use of cover) and survival. 2. Vigilance was significantly higher when individuals fed in smaller groups and in taller vegetation. In the covey period (in early winter when partridges are in flocks), vigilance and use of taller vegetation was significantly higher at sites with higher sparrowhawk predation risk, but tall vegetation was used less by larger groups. Individuals were constrained in reducing individual vigilance by group size and habitat choice because maximum group size was determined by overall density in the area during the covey period and by the formation of pairs at the end of the winter (pair period), when there was also a significant twofold increase in the use of tall cover. 3. Over the whole winter individual survival was higher in larger groups and was lower in the pair period. However, when controlling for group size, mean survival decreased as vigilance increased in the covey period. This result, along with vigilance being higher at sites with increasing with raptor risk, suggests individual vigilance increases arose to reduce short-term predation risk from raptors but led to long-term fitness decreases probably because high individual vigilance increased starvation risk or indicated longer exposure to predation. The effect of raptors on survival was less when there were large groups in open habitats, where individual partridges can probably both detect predators and feed efficiently. 4. Our study suggests that increasing partridge density and modifying habitat to remove the need for high individual vigilance may decrease partridge mortality. It demonstrates the general principle that antipredation behaviours may reduce fitness long-term via their effects on the starvation-predation risk trade-off, even though they decrease predation risk short-term, and that it may be ecological constraints, such as poor habitat (that lead to an antipredation behaviour compromising foraging), that cause mortality, rather than the proximate effect of an antipredation behaviour such as vigilance.

The Context and Quality of Social Relationships Affect Vigilance Behaviour in Wild Chimpanzees

AbstractPrevious studies of vigilance behaviour have focused mainly on the influence of predation threat, whereas the influences of conspecific factors, such as within‐group threats, are relatively unstudied. To elucidate the influences of conspecific factors, this study examined vigilance behaviour in wild chimpanzees (Pan troglodytes schweinfurthii) in Mahale Mountains National Park, Tanzania. Vigilance level was lower during foraging than during resting, which indicated a conflict between vigilance and foraging activity. In addition, vigilance level was higher when chimpanzees were on the ground where an encounter with leopards (Panthera pardus) is likely than when the chimpanzees were in trees. Males, but not females, increased their level of vigilance as the number of individuals within 3 m increased. In both males and females, daily party size – an index of group cohesion – did not affect the vigilance level. The level of maternal vigilance was higher when a dependent infant was separated from its mother than when the offspring was in contact with its mother. Both males and females increased their vigilance when a less‐associated group member was nearby, when compared with when there was no less‐associated group member nearby. This finding suggests that variation in relationship quality influences the vigilance level and that individuals need to increase their level of vigilance when the level of within‐group threats is high. This study indicated that variation in vigilance cannot be understood unless conspecific factors, such as variation in the relationship quality with associates, are considered.

Diurnal spectral EEG fluctuations in narcoleptic patients during rest and reaction time tasks

Narcolepsy is associated with lowered vigilance. Diurnal variation in vigilance appears altered, but the exact nature of this change is unclear. It was hypothesized that the homeostatic sleep drive is increased in narcolepsy. Decreased levels of vigilance are reflected in low frequency band power in the electroencephalogram (EEG), so these frequencies were expected to be increased in the narcolepsy group. Furthermore, it was expected that low frequency power should increase over the day. Narcoleptic patients and healthy controls participated (36 participants in total); they were not allowed to take medication or naps on the experimental day. EEG was measured at 9:00, 11:00, 13:00, 15:00, and 17:00 hours, during rest and during reaction time tasks. In the narcolepsy group, alpha power was lower at rest at all times. Delta and theta power during rest and task performance increased steadily over the day in this group, from 11:00 hours onwards. Additionally, in the narcolepsy group beta1 and beta2 power during rest appeared increased at the end of the day. The effects in the lower frequency bands strongly suggest that vigilance is low at all times. The progressive increase in low frequency power indicates that the sleep drive is enhanced. It is not clear whether this pattern reflects an extreme state of low vigilance, or a pathological brain condition. The effects in the higher frequencies suggest that narcoleptic patients may make an effort to counteract their low vigilance level.

Intra- and interspecific variation in vigilance and foraging of two gerbillid rodents, Rhombomys opimus andPsammomys obesus : the effect of social environment

We studied time budgets in two closely related and ecologically similar gerbillids to test the effect of group size on vigilance and foraging in adult females. Psammomys obesus is strictly solitary, while Rhombomys opimus is mainly social. We compared time budgets of (1) solitary P.obesus females, (2) solitaryR.opimus females and (3) R.opimus females living in male–female pairs. SolitaryR.opimus females spent more time underground, more time in low-cost vigilant postures, moved more, hoarded food more and fed above ground less than paired females. However, females of both categories spent similar time in high-cost upright postures. These results conform mainly to the group size effect hypothesis, while the high level of high-cost vigilance in paired females can be attributed to within-group vigilance, masking the group size effect. Solitary females of P.obesus and R.opimus showed similar time budget patterns; however, P.obesus allocated more time to high-cost vigilance and less time to feeding. In general, differences in time budgets between heterospecific females of the same social status (solitary or paired) were less pronounced than differences between conspecifics of different status. Thus, variation in activity patterns of females can be largely explained by different social conditions rather than by species affiliation. We discuss the results in terms of predation avoidance strategies in solitary and social species.

Yellow‐Footed Rock‐Wallaby Group Size Effects Reflect A Trade‐Off

As group size increases, individuals of many species modify the time allocated to anti‐predator vigilance and foraging. Group size effects can result from a reduction in predation risk or from an increase in competition as a function of aggregation. Anti‐predator models of vigilance and foraging group size effects both predict a non‐linear relationship between group size and time allocation. Linear relationships between group size and time allocation may reflect the modification of such relationships by intraspecific interference competition for limited resources, which would reveal a fundamental cost of sociality. We studied the degree to which group size effects in the yellow‐footed rock‐wallaby (Petrogale xanthopus, a macropodid marsupial) were non‐linear. Like several other macropods, yellow‐footed rock‐wallabies foraged more and looked less as group size increased. Variation in vigilance was best explained by the number of conspecifics within 10 m–a distance substantially less than the 30–50 m often used to quantify group size in macropodids. Linear regressions explained more variation than non‐linear ones, suggesting that wallabies traded‐off the benefits of aggregation with the costs of competition. Moreover, dominant yellow‐foots looked less and tended to forage more than subordinate animals. We hypothesize that competition may be relatively more important in the life‐histories of yellow‐footed rock‐wallabies than those of other macropodid marsupials.

BEHAVIORAL AND ECOLOGIC EFFECTS OF DIFFERENTIAL PREDATION PRESSURE ON MOOSE IN ALASKA

We studied behavioral and ecologic effects of differential predation pressure on moose (Alces alces gigas) in the eastern Talkeetna Mountains, Alaska, during 1996‐1998. Annual mortality from grizzly bear (Ursus arctos) and wolf (Canis lupus) predation was higher for solitary yearling moose than for dependent yearlings (those with adults) and solitary adults. We tested hypotheses that solitary yearlings have heightened levels of vigilance and greater variation in vigilance responses and spend more time near protective cover than do dependent yearlings or adults. Proportion of time spent vigilant did not differ between solitary and dependent yearlings, and no differences were found between solitary yearlings and adults. However, variation in vigilance increased with distance to protective cover for yearlings but not for adults. Only at distances $20 m from protective cover did variation in vigilance differ between solitary yearlings and adults. Increased variation in vigilance at distances far from protective cover, locations where putative vulnerability to predators is greatest, may account for increased mortality among solitary yearlings. Mean distance to protective cover was not different between solitary and dependent yearlings or between solitary yearlings and adults. Because hypotheses regarding differences in vigilance and use of protective cover between age and social status categories generally were not supported, other factors may be involved in promoting high vulnerability of independent yearlings to predation. Smaller body size and maternal defense are unexplored alternatives for explaining differential mortality between yearlings with and without mothers.

Factors affecting vigilance in springbok: importance of vegetative cover, location in herd, and herd size

Vigilance in vertebrates is often inversely related to group size. We present evidence that distance to bushes and location within the herd are also critical factors in vigilance in springbok (Antidorcas marsupialis) in Etosha National Park, Namibia, where they are the preferred prey of cheetahs (Acinonyx jubatus). Most springbok feed in heterospecific herds, both by grazing on grass and browsing on bushes. We studied 1245 animals; variations in vigilance (time alert) were explained by location within the herd, distance to bushes and roads, number of springbok in each herd, and gender and age. Vigilance time decreased with increasing herd size, with increasing distance to bushes and roads, and with density. Springbok on the edge of herds devoted significantly more time to vigilance than did those in other locations, and vigilance in edge animals decreased with group size. Adults were more vigilant than young, and males were more vigilant than females. Position within the herd, and distance from bushes, were the most important variables influencing vigilance. Location in the herd and gender/age affected both browsing and grazing springbok, although other factors accounted for the differences in vigilance between browsing and grazing springbok: 1) group size was not significant for browsers, but it was for grazers, and 2) distances to bushes and road were not significant for browsers, but they were for grazers. These data relate to the risk from predators and the benefits from other group members. Springbok in bushes cannot see all members of the herd, cannot derive early warning from many group members, and are more at risk from predators because the latter can hide in the bushes.

How Much Does Social Group Size Influence Golden Marmot Vigilance?

AbstractA commonly cited benefit of group living is the ability for individuals to reduce the time devoted to scanning for predators with increasing group size - the 'group size effect'. Interestingly, most studies reporting a group size effect have focused on documenting a significant group size effect and did not discuss the relative 'importance' of group size. One way to study the relative importance of group size is to calculate the amount of variation in vigilance explained by group size. I studied effects of social group size on golden marmot (Marmota caudata aurea) vigilance in two ways. First, I estimated the overall amount of time marmots were vigilant during their morning active periods. Second, I estimated the amount of time marmots were vigilant specifically while foraging. Analyses statistically controlled for several factors that have been suggested to confound the study of group size effects. While marmots were active, only 14% of the variation in vigilance was explained by social group size. For foraging marmots, even less variation (about 6%) was explained by social group size. The amount of variation explained by social group size in golden marmots is considerably less that reported in several studies of other species where explained variation was reported or could be estimated from data. Some of the discrepancy between variation explained in this and other studies may stem from my focus on social group size which appears to explain less variation than the more commonly studied foraging aggregation size. However, species differ in the amount of time they devote to foraging and therefore vary in the magnitude of net benefit from group size effects. Future comparative work will be required to rigorously study the relationship between amount of time foraging and the magnitude of group size effects.

EVALUATION OF DAYTIME SLEEPINESS

In summary, the evaluation of the tired patient requires an awareness of the various meanings of tiredness. Furthermore, it is important to differentiate normal sleepiness that is a product of circadian rhythm variation in vigilance from pathologic sleepiness. Sleepiness that results from faulty habits, e.g., altered sleep scheduling, drugs, or sleep restriction, can be readily discerned with the aid of a sleep-wake diary. Because subjective sleepiness is often unappreciated, especially in patients with sleep apnea, methods that rely on self-ratings of the severity of sleepiness, e.g., visual analogue scale, 10-cm line, or SSS may not coincide with performance tasks, observer assessments, or such physiologic methods as the MSLT. Less commonly employed neurophysiologic methods include pupillometry and averaged evoked potentials. On the other hand, the MSLT is commonly used for the detection of physiologic sleepiness. Moreover, it is helpful in evaluating response to treatment. A variation of the MSLT, the MWT, which instructs the individual to remain awake, does not discriminate between sleep onset times for wakefulness and the MSLT for sleepiness in normal subjects. The MWT may be useful for the assessment of treatment responses for excessive daytime sleepiness, e.g., narcolepsy, and for determining the frequency of daytime sleep episodes. The differences that have been observed between behavioral measures and physiologic measures of sleepiness suggest that these techniques assess different aspects of sleepiness. HLA typing (DR2, DQw1) has been shown to be a useful method for corroborating narcolepsy-cataplexy, but the antigens are neither specific for the disorder nor for sleepiness alone.

Variations journalières des composantes des potentiels évolqués cognitifs

Auditory evoked potentials are recorded in 12 subjects 4 times per day: 08 30, 11 30, 14 30 and 18 30. The daily variations of N1, P2, N2 and P3 are studied globally and according to the (morning- or evening) type of subjects. The latency of N2 decreases during the day; it possibly reflects variations in vigilance. The P3 amplitude varies according to the subject typology: for morning-type subjects, P3 is higher in the afternoon than in the morning, and for evening-type subjects, P3 decreases from morning to evening. These evolutions possibly reflect the effort in attention required by different tasks.

Human Operator Efficiency in Monotonous Transport Operations. Effects on Safety

The increasing automation of the operator's cabin as well as the longer distances travelled constitute factors likely to provoke lowered vigilance during critical periods in transport operations. The aim of this laboratory research is to study the capacity of the security system of French trains to detect decreases in vigilance. This system is based on the safety deadman circuit. In order to identify a relationship between motor behavior (activation of the pedal) and variations in vigilance (EEG, eyes blink frequency) a simplified monotonous driving task was used. Main results have shown that during periods of lowered vigilance some perturbations of motor behavior appeared. Futhermore, a degradation of performance in term of increased reaction time and omission of signals was observed during these phases. Main perspectives concern the use of such a system in the detection of decreases in vigilance on the field.

Corrélations entre les variations de la vigilance, l'activité E.E.G., la respiration et les clonies dans 1 cas de maladie de Creutzfeldt-Jakob

Diurnal polygraphic recordings in a 72 year old women with Jakob-Creutzfeldt's disease (confirmed by anatomical and pathological examinations), showed correlations between modifications in respiration and myoclonic activity, and somnolent episodes. Falling asleep was marked by the replacement of periodic paroxystic activity by diffuse and irregular theta activity; the brusts of clonicity were interrupted at the same time as the paroxystic complexes; a more or less marked hypopnea accompanied most of these episodes, but the bradycardia was inconstant. The close temporal correlations between the variations in vigilance, respiration, periodic E.E.G. activity, and clonicity suggested the existence of a common triggering mechanism, the nature of which has still to be elucidated.