Vigilance Rates Research Articles

Predator Vigilance Costs of Allogrooming in Wild Blue Monkeys

AbstractAlthough allogrooming in Catarrhine primates is often interpreted as if it were a costly behavior for the groomer, such costs have not been convincingly documented. This paper presents data on rates of vigilance for aerial predators, measured as looking up toward the sky, in wild blue monkeys engaged in allogrooming, and compares these vigilance rates to those occurring when the same individuals engaged in other activities, namely feeding and resting. Grooming individuals have much lower vigilance rates than resting or feeding individuals, suggesting that grooming individuals are more likely to be at risk of being preyed upon. These results are not caused by a systematic relationship in the sample between activity and either foliage density or time of day, two factors potentially related to levels of safety from predation. Nor was there evidence that blue monkeys avoid the vigilance costs of grooming by engaging in this behavior primarily at safe times or in safe locations. Although the data suggest that vigilance costs occur, they may accrue to the recipient ofgrooming as well as the groomer, and may be compensated for both partners by long- or short-term benefits.

Vigilance, group size and social status in capybaras

Abstract. Capybaras, Hydrochaeris hydrochaeris, live in groups of varying size averaging 10 adults of both sexes. Vigilant behaviour was studied in capybaras under natural conditions, using focal-animal sampling on individual females, dominant males and subordinate males from groups of different sizes. There was a significant negative correlation between group size and individual alert rate, and a positive correlation with total group alert rate. Although the reduction in individual rates of vigilance levelled off at group sizes of 9-10, total alert rate continued to increase. The behaviour of the females accounted for most of the variation in individual alert rate and the behaviour of subordinate males accounted for most of the variation in total alert rate. These results suggest that females benefit the most from being in larger groups due to reduced vigilance required, while subordinate males 'pay' for their group membership by the vigilance they perform.

Differential fitness returns in relation to spatial position in groups.

1. A general overview of position-related fitness differences in group-living animals is given for the first time. 2. Differential fitness returns in groups are often related to competition for resources among group members due to resource limitation. If resources are very scarce, then competition may finally lead to the disbandment of groups. The encounter-dilution effect predicts that grouping confers a benefit if the conspicuousness of large groups does not outweigh the dilution effect and each predator or parasite attacks only one (or a few) prey per encounter (Uetz & Hieber, 1993). While the encounter-dilution effect limits the number of predators and parasites a group is faced with at a given time, marginal predation and communal defence are probably the most important factors for position-related differences in predation risk. 3. Limitation of resources increases competition between groups members and should widen the gap between fitness returns of dominant and subordinate group members. In some group-living animals such as schooling fish, however, predator pressure has apparently selected for uniformity in morphology and behaviour which presumably restricts the potential for resource competition (Magurran & Seghers, 1991). 4. A general problem of assessing individual fitness returns in that different short-term strategies may achieve the same long term goals (Magurran, 1993). The use of feeding rates and predation risks as currencies for fitness returns over short time periods is therefore questionable and can only be a first step. So far, hardly any information is available on long-term effects of differences in positioning behaviour. 5. Food availability and food intake rates tend to be higher in edge positions, whereas energy expenditure does not differ significantly with group position in non-roosting mobile groups. This suggests that edge positions achieve a higher net-energy pay-off and should therefore be preferred by individuals with low energy reserves. 6. Differential predation risks are well documented for stationary and colony-breeding species, but there is a lack of data for mobile, non-breeding species. The reason for the latter is that predation is rarely observed (in the field) and often difficult to relate to group position in fast-moving species such as flocks of birds. Further studies, especially in the field, are needed. 7. Vigilance rates and attack rates do not necessarily give a true reflection of mortality risk. Vigilance is not exclusively related to predation and can be confounded by competition effects and hunger. Attack rates are difficult to translate into per capita risks if hardly any mortality is observed and therefore little information is available about the ratio of successful attacks/total attacks. 8. Most of the literature up to date consists of descriptive studies. There is a need for experimental work that investigate (a) the influence of predator attack mode on differential predation risks; (b) the influence of internal states (such as hunger) on the tradeoff between predation risk and foraging behaviour and its consequences for the positioning behaviour in groups; (c) the 'egalitarian' nature of groups with respect to group position. Do all individuals continuously rotate positions? Or do dominant individuals monopolize certain positions?, and (d) that separate the effects of nutritional state, vigilance and food availability on feeding rates in different group positions. 9. Reproductive success is often related to group position in breeding colonies and lekking animal species. Females probably prefer the safer territories in the group centre, but more empirical data are required to test this hypothesis. 10. Position-related differences in parasitism rate between group members are well documented with per capita rate of parasitism being lower in the centre of groups than at the periphery.(ABSTRACT TRUNCATED AT 400 WORDS)

Patch residence time and vigilance in birds foraging at feeders. Implications of bill shape

During winter small passerines foraging solitarily at feeders showed two different types of vigilance: the vigilance before initiating feeding that is the time needed to assess the potential risks at the patch (waiting time), and the vigilance related to the continuous scanning of the surroundings while foraging (vigilance rate). The waiting time differed significantly among the species, but vigilance rate did not. Patch residence time also differed among the species, being directly related to the waiting time, because the longer the residence time of the forager, the higher the possibility for ambush predators or competitors to reach it. Patch residence time was inversely related to bill length. This probably results from the different quantity of food per foraging time reached by different bill-sized species. Neither waiting time nor patch residence time when solitary were related to social dominance, hoarding behaviour, or species-specific traits associated with the habit of hanging upside down.

Predator vigilance and group size in mammals and birds: a critical review of the empirical evidence.

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.

Vigilance and social organization in two species of primates

Animals that live in groups may accrue anti-predator benefits by virtue of their association with other individuals. While a number of factors (e.g. habitat quality, group geometry, dominance rank) have been shown to affect the relationship between group living and individual rates of visual vigilance, sociality and vigilance have not been studied specifically in terms of the two competing demands they impose upon an individual's visual time. Two captive groups each of tamarins, Saguinus labiatus, and squirrel monkeys, Saimiri sciureus, were used in three related experiments to determine whether they looked at the social or non-social environment while they engated in a simulated foraging task. The tamarins, whose social behaviour is quite pacific and cooperative relative to the more hierarchical squirrel monkeys, looked at the non-social environment when they visually interrupted their foraging. Squirrel monkeys, however, looked more often at group mates. Detection of predators is probably more likely when an individual directs its attention not to conspecifics, but to the environment. Hence, social organizations in which individuals must pay social attention in order to monitor threats and avoid aggression may reduce individual rates of vigilance for predators. Failure to consider various targets of attention may well overestimate vigilance for predators by including other sorts of attentional phenomena in the measurement of vigilance.

The effects of smoking on electrocortical arousal in coronary prone (type A) and non-coronary prone (type B) subjects.

Twenty-nine Type A subjects, (greater than 75 percentile on the Jenkins Activity Survey) and 28 Type Bs (less than 25 percentile of the survey) were asked to smoke one cigarette (1.0 mg nicotine, 16 mg tar, 14 mg CO) using a standardized smoking procedure. Significant differences between baseline and smoking conditions were noted in the distribution of electrocortical activity for both groups. In addition, a shift from EEG low frequency high amplitude (alpha) events to high frequency low amplitude activity (beta) was noted for the As, while the Bs showed enhanced very low frequency high amplitude (theta) activity. A striking parallel was observed between the behavioral predisposition of the subject (A/B) and the possible function of the underlying neurological structure mediating the observed EEG changes. It is suggested that the electrocortical changes observed for the As during smoking are mediated by reticular (ARS I) arousal. Enhanced reticular activity may coincide with an increased rate of information processing, attention and vigilance. On the other hand, the electrocortical changes observed for the Type Bs may represent enhanced activity of the limbic system (ARS II) with could coincide with stimulation of the reward/pleasure centers. Smoking may produce a pattern of neurophysiological arousal which parallels the behavioral tempo of the individual. Possible differences in in vivo regulation of nicotine cholinergic binding sites are also discussed.

Heart rate and GSR concomitants of vigilance and arousal.

Heart rate and GSR concomitants of vigilance and arousal.