Abstract: Group living can confer advantages to individuals, but it can also impose severe costs through resource competition. Kleptoparasitism is one example in which some individuals (joiners) can exploit the food discovered by other animals (finders). This type of social foraging has been modelled either as an information-sharing model or as a producer-scrounger game. An important variable in these models is the finder's advantage: the number of items obtained by the finder before the arrival of other individuals. In this study we describe how the spatial position and rank of individuals in a group of wild tufted capuchin monkeys affect their ability to discover and exploit new food sources. We also analyse the factors that affect the finder's share and the total amount of food obtained by the finder from a newly discovered resource. By placing platforms filled with bananas at novel locations in their home range, we show that animals in the leading edge of a foraging group have a higher probability of discovering new food sources than animals occupying other spatial positions. The alpha male and the alpha female, which tended to occupy central-forward positions, were able to monopolize newly discovered food sources and thus obtain a major share of them. The finder's share at the feeding platforms was smaller when there was more food on a platform, but increased with longer delays before the arrival of other individuals. The total amount of food obtained by the finder from the feeding platforms was larger when there was more food on the platform, when the finder was of higher social status, and when it took longer for other individuals to arrive. Animals can increase their finder's share and total amount consumed from a newly discovered resource by keeping large interindividual distances and by avoiding giving cues about the presence of food (such as food-associated vocalizations) to other animals.

Abstract: Foragers can often show a broad range of strategies when searching for resources. The simplest foraging strategy is to search randomly within a habitat; however, foragers can often assess habitat quality over various spatial scales and use this information to keep themselves in, or direct themselves to, regions of high resource abundance or low predation risk. We investigated models that describe a population of consumers competing for a renewable resource that is distributed among discrete patches. Our aim was to identify what foraging strategy or strategies are expected to persist within a population, where strategies differ in the degree of habitat assessment (i.e. none, local, or global). We were interested in how the optimal strategies are dependent on the cost of assessment and habitat structure (i.e. the variation in renewal rates and predation risks among patches). The models showed that the simple random foraging strategy (i.e. make no habitat assessments) often persisted even when the cost of habitat assessment was low. Persistence could occur when habitat assessment and population dynamics generated an ideal free distribution because it could be exploited by the random foragers. Habitat assessment was more advantageous when consumers could not achieve ideal free distributions, which was more likely as patches became less productive. When productivity was low we sometimes observed the situation where different foraging strategies generated resource heterogeneities that promoted their coexistence, and this could occur even when all patches were intrinsically identical.

Abstract: Primates use social grooming to service coalitions and it has been suggested that these directly affect the fitness of their members by allowing them to reduce the intrinsic costs associated with living in large groups. We tested two hypotheses about the size of grooming cliques that derive from this suggestion: (1) that grooming clique size should correlate with relative neocortex size and (2) that the size of grooming cliques should be proportional to the size of the groups they have to support. Both predictions were confirmed, although we show that, in respect of neocortex size, there are as many as four statistically distinct grades within the primates (including humans). Analysis of the patterns of grooming among males and females suggested that large primate social groups often consist of a set of smaller female subgroups (in some cases, matrilinearly based coalitions) that are linked by individual males. This may be because males insert themselves into the interstices between weakly bonded female subgroups rather than because they actually hold these subunits together.

Abstract: We used a cooperative pulling task to examine proximate aspects of cooperation in captive brown capuchin monkeys, Cebus apella. Specifically, our goal was to determine whether capuchins can learn the contingency between their partner's participation in a task and its successful completion. We examined whether the monkeys visually monitored their partners and adjusted pulling behaviour according to their partner's presence. Results on five same-sex pairs of adults indicate that (1) elimination of visual contact between partners significantly decreased success, (2) subjects glanced at their partners significantly more in cooperative tests than in control tests in which no partner-assistance was needed, and (3) they pulled at significantly higher rates when their partner was present rather than absent. Therefore, in contrast to a previous report by Chalmeau et al. (1997, Animal Behaviour, 54, 1215-1225), cooperating capuchins do seem able to take the role of their partner into account. However, the type of task used may be an important factor affecting the level of coordination achieved. Copyright 2000 The Association for the Study of Animal Behaviour.

Abstract: Breeding groups with multiple stallions occur sympatrically with single-stallion breeding groups in feral horse, Equus caballus, populations. Mutualism and reciprocal altruism between stallions have been proposed to explain the origin and functioning of multistallion bands. However, empirical support for these hypotheses is contradictory and incomplete. Furthermore, there are no explicit tests of the predictions that each hypothesis makes about stallion behaviour and social structure. We compared nine multistallion and 18 single-stallion bands in the Kaimanawa Ranges, New Zealand. Compared with agonistic behaviours, affiliative behaviours were relatively unimportant in the relationships between stallions within bands. The number of stallions in the band did not have a positive influence on mare group size, stability, home range quality or reproductive success in bands. Furthermore, there was a positive relationship between aggression ('intolerance') by the dominant towards subordinate stallions and the subordinates' effort in mare group defence ('helping') but a negative relationship between helping effort by subordinates and their proximity to, and mating with, the bands' mares. Therefore, the predictions of the mutualism and reciprocal altruism hypotheses were not supported. Indeed, for some of the predictions we found the opposite outcomes to be true. Multistallion bands had significantly poorer reproductive success, and dominant stallions were less tolerant of subordinates that helped most and reduced their access to mares. Nevertheless, in all other respects Kaimanawa stallions in multistallion bands behaved like those described elsewhere. Thus, we reject cooperative hypotheses for multimale breeding groups in horses and discuss the mate parasitism and consort hypotheses as better alternatives. Copyright 2000 The Association for the Study of Animal Behaviour.