Predators, food and social context shape the types of vigilance exhibited by kangaroos (original) (raw)
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Behavioral Ecology and Sociobiology, 2009
Vigilance behaviour in gregarious species has been studied extensively, especially the relationship between individual vigilance and group size, which is often negative. Relatively little is known about the effect of conspecifics on vigilance in non-obligate social species or the influence of sociality itself on antipredator tactics. We investigated predator avoidance behaviour in the yellow mongoose, Cynictis penicillata, a group-living solitary forager, and compared it with a sympatric group-living, group-foraging herpestid, the meerkat, Suricata suricatta. In yellow mongooses, the presence of conspecifics during foraging-an infrequent occurrence-reduced their foraging time and success and increased individual vigilance, contrary to the classical group-size effect. Comparing the two herpestids, sociality did not appear to affect overt vigilance or survival rates but influenced general patterns of predator avoidance. Whereas meerkats relied on communal vigilance, costly vigilance postures, and auditory warnings against danger, yellow mongooses avoided predator detection by remaining close to safe refuges and increasing "low-cost" vigilance, which did not interfere with foraging. We suggest that foraging group size in herpestids is constrained by species-distinct vigilance patterns, in addition to habitat and prey preference.
Are the costs of routine vigilance avoided by granivorous foragers?
Functional Ecology, 2011
1. Routine vigilance is an important component of foraging for many species and can occupy a large proportion of this time. Vigilance can conflict with some aspects of foraging (i.e. searching) and, consequently, has the potential to reduce feeding rates by interrupting foraging behaviours. However, for animals that handle food in an upright posture vigilance can be compatible with this portion of handling and, therefore, any vigilance during this time will incur minimal timecosts to foraging. 2. Several functional response models that incorporate vigilance have assumed that, (i) vigilance preferentially occurs during compatible portions of a foraging routine where no costs are incurred; and (ii) vigilance can be treated as a single discrete block of time related in frequency to the feeding rate, i.e. one vigilance scan per feeding event.
The presence of an avian co-forager reduces vigilance in a cooperative mammal
Biology Letters, 2010
Many animals must trade-off anti-predator vigilance with other behaviours. Some species facilitate predator detection by joining mixedspecies foraging parties and 'eavesdropping' on the predator warnings given by other taxa. Such use of heterospecific warnings presumably reduces the likelihood of predation, but it is unclear whether it also provides wider benefits, by allowing individuals to reduce their own vigilance. We examine whether the presence of an avian co-forager, the fork-tailed drongo (Dicrurus adsimilis), affects rates of vigilance (including sentinel behaviour) in wild dwarf mongooses (Helogale parvula). We simulate the presence of drongos-using playbacks of their non-alarm vocalizations-to show that dwarf mongooses significantly reduce their rate of vigilance when foraging with this species. This is, to our knowledge, the first study to demonstrate experimentally that a mammal reduces vigilance in the presence of an avian co-forager.
The effect of social facilitation on vigilance in the eastern gray kangaroo, Macropus giganteus
Behavioral Ecology, 2009
The relevance of vigilance activity to predator detection has been demonstrated in numerous studies. However, few studies have investigated the effect of one group member being vigilant on the probability of others being vigilant in group-forming prey species. Thus, we studied vigilance activity of eastern gray kangaroos Macropus giganteus that still experience occasional predation. We video recorded the behavior of all group members simultaneously and investigated the probability of a focal group member being vigilant (or nonvigilant) in relation to other individuals' vigilant and nonvigilant behaviors. Our results show that the decision of an individual to exhibit a vigilant posture depended on what it and other group members had been doing (scanning or foraging) at the preceding second and on group size. The probability of an individual being vigilant was positively affected by the proportion of companions that were vigilant at the previous second, confirming the existence in this species of a tendency for synchronization of individual vigilance. Group size affected individuals' vigilance in 3 ways. First, individuals were more likely to be vigilant if the proportion of their group mates that was vigilant was high, and this was strengthened with increasing group size. Second, the effect of the individual's own vigilance state (vigilant or not) at the previous second also increased with group size. Third, the probability of an individual being vigilant decreased with group size. These findings increase our understanding of the much-studied relationship between vigilance and group size.
Functions of vigilance behaviour in a social carnivore, the spotted hyaena, Crocuta crocuta
Animal Behaviour, 2010
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. The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.
Animal Behaviour, 2008
Animals gain antipredation benefits from being in larger groups through increased probability of predator detection, dilution of individual risk of being attacked and confusion of predators during attack. A further benefit is that individuals in larger groups can decrease the amount of time they spend being vigilant, while maintaining a high probability of predator detection. They may then gain extra time to forage, so increasing overall intake rate. Increasing group size, however, can also increase competition so that intake rates decrease. We investigated whether there was a foraging benefit in redshanks, Tringa totanus, that show the group size decrease in individual vigilance. Intake rates did not change with group size, despite an increase in time spent foraging. Interference competition increased with group size because individuals travelled more to find prey. Redshanks used the extra time available to forage to maintain intake rates under increased competition. Although the group size effect on vigilance did not accrue direct foraging benefits, larger groups formed, conferring other antipredation benefits. Intake rates were maintained because the interference competition was compensated by the benefits of reduced individual vigilance.
A simple rule for the costs of vigilance: empirical evidence from a social forager
Proceedings of The Royal Society B: Biological Sciences, 2004
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Individual Variation In the Relationship Between Vigilance and Group Size In Eastern Grey Kangaroos
Behavioral Ecology and Sociobiology, 2009
The mean vigilance of animals in a group often decreases as their group size increases, yet nothing is known about whether there is individual variability in this relationship in species that change group sizes frequently, such as those that exhibit fission–fusion social systems. We investigated variability in the relationship between group size and vigilance in the eastern grey kangaroo (Macropus giganteus) by testing whether all individuals showed decreased vigilance with increased group size, as has been commonly assumed. We carried out both behavioural observations of entire groups of kangaroos and focal observations of individually recognised wild female kangaroos. As in other studies, we found a collective group-size effect on vigilance; however, individuals varied in their vigilance patterns. The majority (57%) of the identified individual kangaroos did not show significant group-size effects for any of the recorded measures of vigilance. The females that did not show a negative group-size effect were, on average, more vigilant than those females that did show a group-size effect, but this difference was not significant. We propose that some females exhibit higher levels of social vigilance than others, and that this social vigilance increases with group size, cancelling out any group-size effect on anti-predator vigilance for those females. Our results therefore suggest that only some prey individuals may gain anti-predator benefits by reducing their time spent scanning when in larger groups. The large amount of variation that we found in the vigilance behaviour of individual kangaroos highlights the importance of collecting and analysing vigilance data at the individual level, which requires individual recognition.
Behavioral Ecology and Sociobiology, 2012
Vigilance often decreases with increasing group size, due to lower predation risk or greater scramble competition for food. A group size effect on vigilance is seldom seen in primates, perhaps because scanning and feeding often occur simultaneously or because the distinction between routine and induced vigilance has not been investigated. We analyzed feeding and resting observations separately while distinguishing between routine and induced scans in four groups of wild ursine colobus monkeys (Colobus vellerosus) experiencing scramble competition for food and infanticide risk. We used linear mixed-effect models to test the effect of group size, age-sex class, number of neighbors, number of adult male neighbors, and height in the canopy on scanning rates (vigilance) with and without evident conspecific threat. Food type was also examined in the feeding models. Perceived predation risk affected vigilance more than scramble competition for food and infanticide risk. Routine and induced vigilance were greatest at lower canopy heights during feeding and resting and increased when individuals had fewer neighbors while resting. A group size effect was found on induced vigilance while resting, but scanning increased with group size, which probably indicates visual monitoring of conspecifics. Scanning rates decreased while feeding on foods that required extensive manipulation. This supports the idea that vigilance is relatively cost free for upright feeders when eating food that requires little manipulation, a common feature of folivore diets. In the presence of threatening conspecific males, close proximity to resident males decreased individual vigilance, demonstrating the defensive role of these males in the group.
Behavioral Ecology and Sociobiology, 2008
Theory predicts that individuals at the periphery of a group should be at higher risk than their more central conspecifics since they would be the first to be encountered by an approaching terrestrial predator. As a result, it is expected that peripheral individuals display higher vigilance levels. However, the role of conspecifics in this "edge effect" may have been previously overlooked, and taking into account the possible role of within-group competition is needed. Vigilance behavior in relation to within-group spatial position was studied in impalas (Aepyceros melampus) feeding on standardized patches. We also controlled for food distribution in order to accurately define a "central" as opposed to a "peripheral" position. Our data clearly supported an edge effect, with peripheral individuals spending more time vigilant than their central conspecifics. Data on social interactions suggest that it was easier for a foraging individual to defend its feeding patch with its head lowered, and that more interactions occurred at the center of the group. Together, these results indicate that central foragers may reduce their vigilance rates in response to increased competition. Disentangling how the effects of competition and predation risk contribute to the edge effect requires further investigations.