The Influence of Group Size On Predator Scanning and Foraging Behaviour of Wedgecapped Capuchin Monkeys (Cebus Olivaceus)

We examine vigilance within a mixed-species troop of saddleback (Saguinus fuscicollis) and moustached (Saguinus mystax) tamarins over a complete year. Saddleback tamarins were consistently more vigilant than moustached tamarins. This may be linked to their preference for lower strata. In accordance with previous studies of other primates, vigilant tamarins of both species were significantly further away from their nearest neighbours, and were also at lower heights in the forest than non-vigilant individuals. There was no observed sex difference in the amount of time spent vigilant. In terms of modes of scanning the saddleback tamarins looked up significantly more frequently than the moustached tamarins, whereas there was no difference between the species in the frequency of side sweeps. There were no differences between the sexes in the frequencies of either type of vigilant behaviour. The proportion of time spent vigilant was higher than average immediately prior to entering a sleeping site for saddleback tamarins, but not for moustached tamarins. Both species were more vigilant immediately after exiting a sleeping site than at other times of the day. There was significant variation in the amount of time devoted to vigilance over the course of the year. These findings are discussed with respect to the social structure, ecology, and main predator threats facing these species.

Section: Discussionsupporting

confidence: 84%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Factors affecting vigilance within wild mixed-species troops of saddleback ( Saguinus fuscicollis ) and moustached tamarins ( S. mystax )

Smith

Kelez

Buchanan‐Smith

2004

“…The second case (wedge-capped capuchin, Cebus olivaceus: Robinson 1988a, b) is inconclusive because it did not involve analysis of WGC. Also, vigilance and group size were positively related in both of these cases (Isbell and Young 1993;de Ruiter 1986); large groups may thus have had feeding bene®ts (because their members had less need than members of smaller groups to scan for predators, rather than to feed) that translated into reproductive bene®ts (Janson 1992). …”

Section: Alternative Modelsmentioning

confidence: 99%

The evolution of female social relationships in nonhuman primates

Sterck

Watts

Schaik

1997

1,098

941

Considerable interspeci®c variation in female social relationships occurs in gregarious primates, particularly with regard to agonism and cooperation between females and to the quality of female relationships with males. This variation exists alongside variation in female philopatry and dispersal. Socioecological theories have tried to explain variation in female-female social relationships from an evolutionary perspective focused on ecological factors, notably predation and food distribution. According to the current``ecological model'', predation risk forces females of most diurnal primate species to live in groups; the strength of the contest component of competition for resources within and between groups then largely determines social relationships between females. Social relationships among gregarious females are here characterized as Dispersal-Egalitarian, Resident-Nepotistic, Resident-Nepotistic-Tolerant, or Resident-Egalitarian. This ecological model has successfully explained di erences in the occurrence of formal submission signals, decided dominance relationships, coalitions and female philopatry. Group size and female rank generally a ect female reproduction success as the model predicts, and studies of closely related species in di erent ecological circumstances underscore the importance of the model. Some cases, however, can only be explained when we extend the model to incorporate the e ects of infanticide risk and habitat saturation. We review evidence in support of the ecological model and test the power of alternative models that invoke between-group competition, forced female philopatry, demographic female recruitment, male interventions into female aggression, and male harassment. Not one of these models can replace the ecological model, which already encompasses the between-group competition. Currently the best model, which explains several phenomena that the ecological model does not, is a``socioecological model'' based on the combined importance of ecological factors, habitat saturation and infanticide avoidance. We note some points of similarity and divergence with other mammalian taxa; these remain to be explored in detail.

“…Many researchers have reported a reduction in individual vigilance with increasing group size (review: Elgar 1989; Roberts 1996). Furthermore, individuals were found to be more vigilant in positions of higher predation risk: exposed areas on the ground, exposed branches in the canopy, at the periphery of the group, and with less neighbours around (Hamilton 1971;Lipetz and Beko 1982;de Ruiter 1986;Roberts 1988;van Schaik and van Noordwijk 1989;Cords 1990;Bedneko and Ritter 1994;Burger and Gochfeld 1994;Rose and Fedigan 1995). Behav Ecol Sociobiol (1999) 45: 137±150 Mate defence is very common whenever females can be monopolised by males (van Hoo and van Schaik 1992).…”

Section: Introductionmentioning

confidence: 99%

Vigilance in wild Thomas's langurs ( Presbytis thomasi ): the importance of infanticide risk

Steenbeek

Piek

Buul

et al. 1999

This study examines vigilance as a behavioural indicator of the importance of infanticide risk by comparing the infanticide avoidance hypothesis with the predation avoidance and mate defence hypotheses for wild Thomas's langurs (Presbytis thomasi) in Sumatra. We found that all individuals were more vigilant in situations of high predation risk, i.e. lower in the trees and in the absence of neighbours. Females were also more vigilant on the periphery of the group. However, there were variations in vigilance levels that could not be accounted for by the predation avoidance hypothesis. Males without infants showed higher levels of vigilance in areas of home range overlap than in non-overlap areas during the early phase of their tenure, strongly suggesting mate defence. In these areas of home range overlap where Thomas's langur groups can interact, males may attack females and infants, and so the infanticide risk for males and females with infants is likely to be high in these areas. Only females with infants, but not males with infants or females without infants, showed higher vigilance levels in overlap areas than in non-overlap areas; in addition, in overlap areas, females with an infant were more vigilant than females without an infant, while this was not the case in non-overlap areas. Both females and males with infants were more vigilant high in the trees than at medium heights in overlap areas but not elsewhere. These ®ndings can only be explained by the infanticide avoidance hypothesis. In contrast to predator attacks, infanticidal male attacks come from high in the canopy, and only occur in overlap areas. There was a signi®cant sex dierence in vigilance, but males were only more vigilant than females without an infant, and not more vigilant than females with an infant. We conclude that vigilance varied mainly in relation to the risk of predation and infanticide. Mate competition only played a role for males during the early phase of their tenure. Predation risk seems to oer the best explanation for vigilance for all individuals in the absence of infants. Both predation risk and infanticide risk played a role for females and males with infants.