Vigilance Patterns Research Articles

Toward an individual-level understanding of vigilance: the role of social information

A gregarious lifestyle affords the benefit of collective detection of predators through the many-eyes effect. Studies of vigilance are generally concerned with exploring the relationship between vigilance rates and group size. However, a mechanistic understanding of the rules individual animals use to achieve this group-level behavior is lacking. Building on a previous modeling approach, we suggest that individuals reconcile their own private information against the social information they receive from their group mates in order to decide whether to feed or be vigilant at any one time. We present a novel modeling approach utilizing a Markov chain Monte Carlo process to describe the transition between vigilant and nonvigilant states. Many of our assumptions are based qualitatively on recently published experimental observations. We vary the amount of social information and the fidelity with which individuals process this information and show that this has a profound effect on the individual vigilance rate, the individual vigilant bout length, and the proportion of vigilant individuals at any one time. A wide range of group-level vigilance patterns can be obtained by varying simple behavioral characteristics of individual animals. We find that generally, increasing the amount of, and sensitivity to, social information generates a more cooperative vigilance behavior. This model potentially provides a theoretical and conceptual framework for examining specific real-life systems. We propose analyzing individual-based data from real animals by considering their group to be a connected network of individuals, with information transfer between them.

Nonrandom patterns of vigilance in flocks of the greater flamingo, Phoenicopterus ruber ruber

Models of vigilance in groups usually assume instantaneous randomness in scan initiation and sequential randomness in the duration of successive interscans, thus predicting a negative exponential distribution of interscan durations and no predictability in the duration of successive interscans. However, recent models suggest that scanning should instead occur regularly rather than randomly when foragers are threatened by nonobservant predators, thus predicting interscans of constant duration and predictable interscan sequences. I examined whether vigilance patterns departed from instantaneous and sequential randomness in greater flamingos wintering in a tropical lagoon complex in Venezuela. Predation risk in this large species is almost nonexistent, and it is argued that disturbance by people, the most probable threat, should best be detected using a regular pattern of scanning. As predicted, the distribution of interscan durations showed a strong central tendency and differed significantly from the expected negative exponential distribution. Interscan intervals of similar duration occurred in succession more often than predicted by chance. Despite obvious departures from instantaneous and sequential randomness, substantial variability remained in the distribution of interscan durations, and several interscan sequences were quite unpredictable. I relate these findings to potential variation in food supply within the confine of a flock and pre-emptive scans to detect potential threats.

Behavioural and physiological responses of naïve European rabbits to predator odour

Animals show a variety of antipredator strategies in response to the presence of chemical cues from mammalian predators. Nevertheless, there is no general agreement as to whether recognition of predator odours is dependent upon experience. We conducted an experiment on European rabbits Oryctolagus cuniculus naive to any contact with predators and we investigated (1) whether they possessed a mechanism for the recognition of the odour of a predator, and (2) how they responded behaviourally and physiologically to that odour. We used fox Vulpes vulpes faeces as the source of the predator odour and sheep Ovis aries faeces as a nonpredator control odour. The experiments were conducted in small outdoor enclosures where the animals were kept singly. We recorded patterns of vigilance, activity and feeding, and changes in glucocorticoids and body mass. The rabbits showed a clear antipredator response to the presence of fox faeces, whereas they behaved neutrally in response to sheep odour. The response consisted of increased avoidance and vigilance while feeding and more investigation before feeding. Furthermore, the rabbits showed a physiological alarm response, that is, an increased responsiveness of their adrenocortical system and weight loss. However, the total activity budget, measured as time spent outside the burrow, the time spent feeding, and the amount of food ingested remained largely stable during the experiment. We conclude that rabbits recognised predator odours and that this recognition was independent of experience.

The effect of sward height and drainage on Common Starlings Sturnus vulgaris and Northern Lapwings Vanellus vanellus foraging in grassland habitats

Agricultural change is often cited as a causal factor in the decline of the UK's farmland birds because bird declines have mirrored changes in agricultural practices. Although much is known about the mechanisms driving population declines on arable systems, mechanisms in grassland systems are relatively poorly studied, despite receiving a similar degree of intensification. Agricultural intensification may affect bird declines by reducing food abundance or accessibility, forager mobility or predation risk. Here we examine experimentally the effects of sward height on the foraging behaviour of adult Common Starlings Sturnus vulgaris, and the effects of sward height and drainage on the behaviour of Northern Lapwing Vanellus vanellus chicks. Both species are declining across the UK and both forage in farmed grassland habitats, but they differ in their foraging methods because Starlings probe for soil invertebrates whereas Lapwing chicks glean prey from surfaces. Overall, after controlling for prey abundance, short swards were found to be more productive for both species. Prey capture rate within foraging bouts did not differ with sward height for Starlings, but Starlings spent more time foraging on short swards and captured 33.2% more prey. Starlings walked more steps on short swards. Lapwing chick foraging rates declined as sward height increased. Soil moisture was not found to be a predictor of Lapwing chick foraging rates within the observed range. Our results suggest that short swards are a more profitable foraging habitat for soil and surface invertebrate feeders. Short swards may facilitate surface prey detection, improve forager mobility and increase foraging time by altering vigilance patterns. Provision of short swards in areas where these are lacking could be simple method of improving foraging habitats for grassland birds.

The effect of limited visibility on vigilance behaviour and speed of predator detection: implications for the conservation of granivorous passerines

Foraging animals frequently change their pattern of vigilance when they move from a patch with a clear view to one with a relatively obstructed view. This has been widely interpreted as compensation for a reduced ability to detect approaching predators in obstructed habitats. We test the extent to which changes in vigilance may compensate for the effect of reduced visibility on an animal's ability to detect predators. We measured the vigilance, foraging and speed of predator‐response behaviours of lone chaffinches Fringilla coelebs that fed on seeds (800 per m2) scattered on artificial stubble habitats (with either a clear view of surroundings or an obstructed view). On both treatments, individuals with more rapid head‐up rates responded more quickly to a flying model sparrowhawk Accipiter nisus (P=0.04); as did individuals with shorter food‐search times (P=0.02). However, neither head‐up rate nor food‐search period varied with obstruction. Based on research previously published using this system, we suggest that this is because individuals are constrained in their ability to increase head‐up rate because doing so is largely determined by their individually determined foraging efficiency. Instead chaffinches increased the duration of their head‐up periods by 13% in the visually obstructed treatment (long stubble) and peck rates were 13% lower. Despite this presumed attempt to compensate for reduced visibility, duration of head‐up period had no effect on response time of the fast‐moving predator in our experiment and birds were 24% slower to respond in the long stubble. Rather than being maladaptive, increasing head‐up duration may have been related to enhanced detection of other predator types, for example stalkers. Our results have implications for the conservation of wild granivorous birds. They support the view that agroeconomic decisions that affect micro‐habitat structure over a large scale could affect predation risk, habitat choice and the conservation status of granivorous birds.

Incompatibility between antipredatory vigilance and scrounger tactic in nutmeg mannikins, Lonchura punctulata

Most social foragers must search for food while avoiding predators. Group-foraging nutmeg mannikins engaged in a producer–scrounger game search for their own food (play producer) by hopping with the head down and search for others' food discoveries (play scrounger) by hopping with the head up. If the scrounger tactic is compatible with antipredatory vigilance, then an increase in antipredatory vigilance should lead to the detection of more joining opportunities, and hence to more joining by foragers. We tested this prediction as well as the extent to which stationary birds use head up exclusively for antipredatory purposes and hopping birds use head up for foraging purposes only. We observed three flocks of nutmeg mannikins searching for hidden clumps of food in an indoor aviary. We used a 2×2 factorial design in which both the distance to a safe refuge and the food distribution were manipulated. The use of head up by stationary and eating birds increased significantly with increased distance to cover. Distance to cover, however, had no effect on the use of the scrounger tactic or on the level of joining. We found no evidence of compatibility between the scrounger tactic and antipredatory vigilance. Our results provide the first unambiguous evidence for the existence of two distinct and incompatible patterns of vigilance for predators and for conspecifics. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

Vigilance in Greater Flamingos Foraging at Night

AbstractVigilance studies have mostly focused on adaptive changes in antipredator behavior during the day. Adjustments in vigilance patterns in species that also forage at night are poorly known. Birds may forage at night to evade predation or other sources of disturbance, in which case levels of vigilance are expected to decrease at night. However, low visibility at night, especially on moonless nights, may compromise visual detection of predators, in which case levels of vigilance are expected to increase at night. We examined the effect of time of day on vigilance in non‐breeding Greater Flamingos foraging in a tropical lagoon complex in Venezuela. Vigilance increased on darker nights but overall levels of vigilance at night did not differ from daytime values. Vigilance decreased with group size in a similar fashion both during day and night. Flamingos foraged in smaller flocks at night than during the day. The occurrence of small flocks, in which vigilance was quite high, and the increase in vigilance on dark nights imply that the amount of time allocated to foraging must be generally lower at night in flamingos. The results suggest that the night was not perceived as safer by foraging flamingos, and that visual detection of predators was probably compromised by low light levels.

Changes in vigilance with group size under scramble competition.

Animals often interrupt foraging to scan the surrounding environment. In several taxa, such vigilance decreases with group size (Elgar 1989). The decline in vigilance is usually interpreted as a decrease in the predation risk to an individual in large groups. Mechanisms such as increased detection ability and numerical dilution of risk may provide more protection to foragers in large groups, thus leading to lower vigilance (Pulliam 1973; Roberts 1996; Bednekoff and Lima 1998). Nevertheless, recent work indicates that the decrease in vigilance with group size may be mitigated against if individuals in large groups scan more to avoid displacements by aggressive companions (Slotow and Coumi 2000; Treves 2000) or to locate the food discoveries of other group members (Beauchamp 2001). We explore the role of resource availability on vigilance patterns. In earlier vigilance models, a decrease in vigilance would allow foragers either to decrease the total amount of time needed to accumulate a fixed amount of resources (Pulliam et al. 1982) or to increase feeding rate over a given time horizon (McNamara and Houston 1992). In either case, no competition for resources is assumed to take place. However, when resources are limited, a reduction in vigilance may allow individuals to allocate more time to foraging and so obtain a greater share of the re-

Eat or be eaten: predator sensitive foraging among primates

Preface 1. An introduction to predator sensitive foraging Lynne E. Miller Part I. Biological Variables: 2. Dangers in the dark: are some nocturnal primates afraid of the dark? Simon K. Bearder, K. A. I. Nekaris and Courtney A. Buzzell 3. Predation sensitive foraging in captive tamarins Mark J. Prescott and Hannah M. Buchanan-Smith 4. Seeing red: consequence of individual differences in color vision in callitrichid primates Nancy G. Caine 5. Predator sensitive foraging in Thomas langurs Elisabeth H. M. Sterck Part II. Social Variables: 6. The role of group size in predator sensitive foraging decisions for wedge-capped capuchin monkeys (Cebus olivaceous) Lynne E. Miller 7. Group size effects on predation sensitive foraging in wild ring-tailed lemurs (Lemur catta) Michelle L. Sauther 8. Species differences in feeding in Milne Edward's sifakas (Propithecus diadema edwardsi), rufus lemurs (Eulemur fulvus rufus) and red-bellied lemurs (Eulemur rubriventer) in southeastern Madagascar: implications for predator avoidance Deborah J. Overdorff, Suzanne G. Strait and Ryan G. Seltzer 9. Evidence of predator sensitive foraging and traveling in single- and mixed-species tamarin troops Paul A. Garber and Julio Cesar Bicca-Marques 10. Predator (in)sensitive foraging in sympatric female vervets (Chlorocebus aethiops) and patas monkeys (Erythrocebus patas): a test of ecological models of group dispersion Lynne A. Isbell and Karen L. Enstam 11. Predation risk and anti-predator adaptions in white-faced sakis (Pithecia pithecia) Terrence M. Gleason and Marilyn A. Norconk Part III. Environmental Variables: 12. Foraging female baboons exhibit similar patterns of antipredator vigilance across two populations Russell A. Hill and Guy Cowishaw 13. Foraging and safety in adult female blue monkeys in the Kakamega Forest, Kenya Marina Cords 14. Predicting predation risk for foraging arboreal monkeys Adrian Treves 15. Predator sensitive foraging in ateline primates Anthony Di Fiore 16. Anti-predatory behaviour in gibbons (Hylobates lar, Yai/Thailand) Nicola L. Uhde and Volker Sommer.

Processing bias for aggression words in forensic and nonforensic samples

Presenting stimuli that are salient to their concerns produces particular patterns of avoidance or vigilance in both clinical and nonclinical populations. To date, no research has explored if this effect extends to forensic populations when presented with violently themed stimuli. Such material can be seen as potentially salient to those people who might habitually resort to aggression. To test this prediction, two studies (a dot-probe and emotional Stroop) examined the effect of presenting aggressively themed words to a group of offenders and undergraduates. Violent offenders (as classified by their index offence) demonstrated significant response biases to aggression words in both tests. This effect was also found in the aggressive undergraduates (as classified by anger scores on the Buss-Perry Aggression Questionnaire). These data confirm the saliency of aggression words to aggressive individuals and suggest that these simple cognitive tests may offer a potential objective measure of assessment in forensic populations.

Social monitoring and vigilance behavior in brown capuchin monkeys ( Cebus apella )

I investigated the vigilance behavior of brown capuchin monkeys (Cebus apella) in Iguazu, Argentina to determine the relative importance of anti-predatory vigilance versus social monitoring. Predator detection has been found to be the major factor driving vigilance patterns in other populations of Cebus, and a positive relationship between vigilance and the number of nearby neighbors has been found. In the Iguazu population, social monitoring is the primary function of vigilance, as indicated by a negative relationship between vigilance and neighbor density. Even if social monitoring and predator detection are totally compatible, the time tradeoffs associated with vigilance behavior are mostly driven by social monitoring in this population. In addition to recording vigilance data in relation to the number of neighbors, several other variables were recorded in conjunction with vigilance behavior in order to control for possible confounding factors. After controlling for these factors, it was found that the number of neighbors within 10 m was still highly correlated with the percent of time spent vigilant. The average percent of time spent vigilant was found to be much lower in Iguazu, compared to another population of C. apella with higher predation pressure. The average vigilance bout was much closer in length to known social monitoring bouts than to known anti-predatory vigilance bouts. These patterns indicate that the predominate function of vigilance in this population of C. apella is social monitoring. In populations with low predation pressure, the time costs associated with social monitoring should increase with group size, and increasing neighbor density. The fitness costs of social monitoring have not been incorporated into current social models, and these results indicate that these models may not be appropriate for all study populations.

Vigilance in human groups: a test of alternative hypotheses

Abstract Humans exhibit the same inverse relationship between group size and vigilance rates that has been classically described in animals. We collected data on natural human vigilance behaviour in two different contemporary environments (a large refectory-style cafeteria and open parks) to test between four alternative hypotheses for this relationship: predation risk, searching for friends, mate searching and mate guarding. The results demonstrate that, at least in contemporary city environments, humans monitor their surroundings largely for reasons motivated by mate searching. Data on whom subjects look at in a busy environment indicate that males are significantly more likely to attend differentially to female passers-by, but that females show a less clear-cut discrimination. We conclude that vigilance patterns are determined by locally salient functions.

Analysis of Mid-Air Collisions in Civil Aviation

Mid Air Collisions (MAC) are tragic events, with the potential of multiple fatalities. Despite the improving trends in aviation safety, the rate of MAC has remained stable for the past few years. There is an absence of published literature on MAC and related human performance issues. Consequently, this study analyzed 79 mid air collisions in civil aviation in the United States from 1994 to 1999 in an attempt to further understand the causes of these accidents. Contextual data was analyzed in terms of accident location, phase of flight, type of aircraft operation, visibility conditions, and direction of aircraft trajectories (same vs. opposite direction). Pilot factors were also examined, including recent flying experience and medical certification. An attempt is made to interpret the results in terms of recent models of pilot vigilance and scan patterns. Recommendations are made for possible future research in the area.

Vigilance and aggregation in black howler monkeys ( Alouatta pigra )

Animals are expected to reduce per capita vigilance with increasing group size. Widespread support for this expectation has been found in studies of birds and ungulates. Primate vigilance patterns appear to differ, but studies of primates may have sampled groups with too many members to detect intergroup differences in vigilance. We tested this idea by measuring individual vigilance rates in wild black howler monkeys (Alouatta pigra) living in stable groups of two to ten individuals. No group size effect on vigilance emerged. As in previous studies, inter-individual proximity explained variation in individual vigilance rates. Focal animals with associates within 2 m and with multiple associates in the same tree were less vigilant than isolated animals. Activity and class of focal animals as well as the presence of neonates influenced the average vigilance of adult and subadult black howler monkeys. We conclude that functional explanations must be considered for the general lack of a group size effect on primate vigilance.

Patterns of Flock Size, Diet, and Vigilance of Naturalized Monk Parakeets in Hyde Park, Chicago

Patterns of Flock Size, Diet, and Vigilance of Naturalized Monk Parakeets in Hyde Park, Chicago

Patterns of Flock Size, Diet, and Vigilance of Naturalized Monk Parakeets in Hyde Park, Chicago

Abstract We examined patterns of diet, foraging group size, and vigilance effort of naturalized Monk Parakeets (Myiopsitta monachus) in Hyde Park, a neighborhood of Chicago, Illinois. Parakeets exhibited a highly seasonal and varied diet consisting of fruits, seeds, and buds, and they fed almost exclusively on birdseed provided at backyard feeding stations during the winter months. Birds foraged in groups of 1 to 31 birds, but most flocks were of 10 birds or less. Foraging group size was greatest in the fall and early winter, and smallest at the beginning of the spring when breeding began. Monk Parakeets adjusted their vigilance effort with changes in flock size. Individual vigilance effort declined with increasing flock size through a decrease in time spent scanning as well as the number of times scans were initiated. The number of parakeets exhibiting vigilance in a flock at any given time also decreased with flock size. It is likely that the highly adaptable and varied diet of Monk Parakeets contributes greatly to the persistence and growth of populations in a variety of North American habitats.

VIGILANCE IN BRONZE MANNIKIN GROUPS: THE CONTRIBUTIONS OF PREDATION RISK AND INTRA-GROUP COMPETITION

Abstract We describe foraging behaviour and time budgets of the gregarious bronze mannikin, Lonchura cucullata. In addition to being the first such study of a southern African granivore, this was the first study of a group-forager to differentiate between vigilance for other flock members (conspecifics) and vigilance for predators. We verified a perception of predation risk by placing five feeders at increasing distances from cover. The mean number of birds at a feeder decreased significantly with increasing distance from cover. We manipulated levels of aggression by restricting access to random numbers of feeding holes at various distances. The treatments succeeded in forcing birds to feed further from cover, and by inference, increased levels of aggression. We measured time budgets with focal samples on marked individuals. There was no influence of group size on time budgets. There was a non-significant (p < 0.06) trend for vigilance to increase with increasing distance from cover (predation risk). There was no pattern in the relative vigilance for predators as opposed to vigilance for other flock members (conspecifics), either with group size, distance from cover, or manipulated levels of aggression. Despite our inability to detect patterns of vigilance for other flock members, we emphasize the importance of studies to elucidate such a process.

Within-group vigilance in red colobus and redtail monkeys.

In theory, animals are expected to relax vigilance in the safety of large groups. Four controlled studies of primates have failed to detect relaxed vigilance as group size increases. The counter-intuitive behavior of primates might arise if another component of vigilance increases with group size, masking any decrease in outward, anti-predator vigilance. Surveillance of associates is a major component of primate vigilance and might be expected to increase with group size due to an increase in competitive interactions. The present analysis uses data on glances toward associates to determine if within-group surveillance is related to group size in wild red colobus and redtail monkeys of Uganda. Although males glance at associates more frequently during mating periods and females glance at associates more often when infants are young or out of contact, there was no evidence of a group-size effect on within-group surveillance. As with previous studies, primate vigilance patterns reflect reproductive strategies such as infant protection and mate defense. This study joins several others that indicate that primate vigilance is unresponsive to group size. New models that take into account association patterns below the level of the group may be needed.

Feeding and vigilance behaviour of breeding ostriches (Struthio camelus) in a farming environment in Britain

1. Vigilance and feeding behaviour of male and female adult breeding ostriches were recorded to determine feeding and scanning bout lengths, a time budget and the pattern of vigilance immediately after food was provided. 2. Males were more vigilant and fed for shorter periods than females immediately after concentrate food was delivered but not throughout the whole day. 3. Most interscan periods of males were below 40 s with a maximum of 90 s compared with most interscan periods of females lasting less than 70 s with a maximum of 160 s. 4. Gender differences in behaviour are attributed to increased male vigilance for predators and/or conspecifics, and increased female feeding required for egg production and greater opportunity to feed because of male vigilance.

The Role of Vigilance in the Survival and Reproductive Strategies of Desert Baboons

This study investigates the relative importance of vigilance in the survival strategies (detection of predators) and reproductive strategies (detection of mates and competitors) of adult baboons Papio cynocephalus ursinus among four groups in a desert population. The proportion of time spent vigilant under a variety of conditions was quantified through instantaneous sampling of focal individuals. Matched comparisons were then conducted to test six predictions for each functional explanation (survival or reproduction). These relate vigilance to (1) sex, (2) group size, (3) activity, (4) habitat, (5) refuge use and (6) spacing behaviour. Vigilance levels do not differ between sexes or groups. However, females are more vigilant when engaged in high-risk activities, when distant from refuges and when distant from neighbours. Male vigilance similarly covaries with refuge use and spacing behaviour, but males are not always more vigilant in dangerous activities and show greater vigilance in open rather than closed habitats. According to the predictions tested, the results provide partial support for the proposal that vigilance plays a role in predator detection for both sexes, although in males the detection of potential mates and competitors appears to be of greater importance. There was no evidence that males provide a vigilance service for females. Vigilance patterns are complicated by activity constraints and the multifactorial nature of anti-predator strategies.