Habitual cave use and thermoregulation in chacma baboons (Papio hamadryas ursinus)

The willingness to utilise caves as shelters is held to have been important to early humans but dependent on pyrotechnology. Despite anecdotal evidence that non-human primates will also exploit caves there has as yet been no detailed account of such exploitation or of the reasons underlying it. Here we provide the first such data, on the frequency and patterning of the use of an underground cave system by baboons (Papio hamadryas)-and show that usage is determined, at least in part, by above-ground temperatures.

Female baboons do not raise the stakes but they give as good as they get

We used data from four chacma baboon, Papio cynocephalus ursinus, troops, living in two populations, to test the raise the stakes (RTS) strategy of reciprocity. Female baboons did not raise the stakes either within or across grooming bouts. Instead they time-matched grooming contributions and divided grooming into short episodes. In addition, analysis of the grooming behaviour of frequently versus infrequently grooming dyads did not reveal differences in grooming patterns predicted by the RTS strategy. We suggest time constraints preclude the escalation of grooming bout length as required by RTS; the data were more consistent with a strategy of give as good as you get. However, this strategy could not explain all the patterns observed, and we conclude that biological market theory represents a more appropriate framework for investigating female grooming dynamics than dyadic games based on the iterated prisoner's dilemma. We suggest that competitive altruism among individuals acts as a market force influencing an individual's value as a grooming partner. Copyright 2000 The Association for the Study of Animal Behaviour.

Effects of sexual dimorphism on facial attractiveness

Testosterone-dependent secondary sexual characteristics in males may signal immunological competence and are sexually selected for in several species. In humans, oestrogen-dependent characteristics of the female body correlate with health and reproductive fitness and are found attractive. Enhancing the sexual dimorphism of human faces should raise attractiveness by enhancing sex-hormone-related cues to youth and fertility in females, and to dominance and immunocompetence in males. Here we report the results of asking subjects to choose the most attractive faces from continua that enhanced or diminished differences between the average shape of female and male faces. As predicted, subjects preferred feminized to average shapes of a female face. This preference applied across UK and Japanese populations but was stronger for within-population judgements, which indicates that attractiveness cues are learned. Subjects preferred feminized to average or masculinized shapes of a male face. Enhancing masculine facial characteristics increased both perceived dominance and negative attributions (for example, coldness or dishonesty) relevant to relationships and paternal investment. These results indicate a selection pressure that limits sexual dimorphism and encourages neoteny in humans.

Success breeds success in mating male reed frogs (Hyperolius marmoratus)

Studies of the distribution of mating success among males in frog choruses typically seek to identify specific phenotypic attributes that confer a higher mating success on certain individual males. These attributes invariably relate to competition among males: either direct competition in the form of aggression, or competition to attract and be chosen by females. In this paper, we present evidence that an additional factor may operate in frog choruses. We show that individual males who mate on a given night enjoy a higher probability of being successful on the next night, and we suggest that this is because successful mating enables males to conserve energy.

Mate guarding and risk assessment by male mountain baboons during inter-troop encounters

Aggressive herding of females is a frequent but not invariant response by male savannah baboons, Papio cynocephalus, to encounters with other troops. While males in some troops are consistently more likely to herd than those in others, not all inter-troop encounters result in herding, even within particular troops. This suggests that males assess the risk of male invasion posed by each encounter and respond accordingly. We used data from baboon troops in the Drakensberg mountains to determine the rules males follow in deciding whether to herd. Consistent differences between troops were explained only by the adult sex ratio. Males were more likely to herd if the sex ratio of their own troop was female biased, a finding that is concordant with the observation that males are more likely to immigrate into troops where the sex ratio is more female biased than the population average. Differences within troops were a consequence only of encounter distance, with herding being more likely at closer distances. We found a negative correlation between the angle of approach to the other troop and the subsequent angle of deflection. We interpret this to mean that herding functions to increase the distance between the interacting troops, thereby curtailing opportunities for strange males to inspect the troop and determine its sex ratio. In this way, possibly unlike those in other populations, the decision rules of these male baboons are geared to protecting longer-term reproductive prospects. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1997 The Association for the Study of Animal Behaviour.

Cohort size and the allocation of social effort by female mountain baboons

Dunbar (1992,Behav. Ecol. Sociobiol.33, 35-49) argued that constraints on social time limited the size to which savannah baboon, Papio cynocephalustroops in any given population could grow before fissioning. Since this should be reflected in population structure, we have elsewhere (Henzi et al. 1997a, Anim. Behav. 53, 525-535) constructed a model, based on a rising probability of fission, that fits the observed distribution of troop sizes of mountain baboons, P. c. ursinusin the Drakensberg mountains of South Africa and which predicts that the probability of fission will rapidly increase once a troop has more than 23 members (or 8.7 females). We test this prediction in this paper. Since Dunbar argued that females will drive fission once they cannot engage in the grooming necessary to sustain alliances, we compared the grooming interactions of adult females from four troops in the Drakensberg mountains. The mean female grooming clique size reached an asymptote at 7.4 females, so that females in cohorts of eight or more no longer attempted to groom all other females, and mean grooming bout length declined as the cohort grew to 7.9 females and then increased again. These values are coincident with the female cohort size predicted by our model of troop growth and fission. We argue that females attempt to groom all other females as well as sustain closer relationships with a few females through longer bouts of reciprocated grooming. When the demands of grooming all other females reduce bout length to a point when no reciprocated bouts are possible, female clique size is capped. As a troop continues to grow, the mechanical difficulties involved in gaining access to grooming partners leads to a reduction in the diversity of grooming relationships. This weakening of the total female network, as cliques become more differentiated, is likely to facilitate fission. We conclude that our data provide the first within-population validation of Dunbar's hypothesis concerning the mechanism underpinning fission. In the Drakensberg, where there is no advantage to female coalitions, we propose, as an amendment, that females will leave a troop not to escape local competition, but to follow a male with whom they have a close friendship.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Dietary and foraging strategies of baboons

As large-bodied savannah primates, baboons have long been of special interest to students of human evolution: many different populations have been studied and dietary comparisons among them are becoming possible. Baboons' foraging strategies can be shown to combine high degrees of flexibility and breadth with selectivity. In this paper we develop and test multivariate models of the basis of diet selection for populations of montane and savannah baboons. Food selection is positively related to protein and lipid content and negatively to fibre, phenolics and alkaloids. Seasonal changes in dietary criteria predicted by these rules are tested and confirmed. Although nutritional bottlenecks occur at intervals, a comparison between long-term nutrient intakes in four different populations indicates convergence on lower degrees of variation than exist in superficial foodstuff profiles.

Diet and feeding behaviour of samango monkeys (Cercopithecus mitis labiatus) in Ngoye Forest, South Africa

The samango monkey occurs at the southern limit of the range of Cercopithecus mitis. Greater climatic seasonality at this latitude results in more predictable fruiting patterns. In addition, there are no diurnal sympatric primate frugivores. Under these conditions, the diet and feeding strategies of samango monkeys would be expected to differ notably from those of central or east African C. mitis subspecies. Contrary to these expectations, the preliminary observations reported here indicate that diets of samango and blue monkeys differ only superficially in the proportions of items eaten. Similarities in feeding behaviour are especially marked during the dry season period when fruit is not abundant. Both samango and blue monkeys tend to be less selective in their choice of food species and to eat available food species regardless of their energy content; a shift toward less nutritious items such as leaves is also noted. Feeding behaviour during the summer wet season is characterized by the selection of fruits with high-energy values. A high proportion of visits by the monkeys to areas of greater food availability suggests a concentration of feeding effort in food patches and the selection of higher energy food species within patches.

Breeding season influxes and the behaviour of adult male samango monkeys (Cercopithecus mitis albogularis)

Troops comprising a high density population of samango monkeys (Cercopithecus mitis) in Natal province, South Africa, experienced an influx of adult males during the breeding season. Observation of one troop revealed that these males competed with one another and with two resident males for access to receptive females. Although both sexes initiated copulation, attempts to do so were more often successful if female-initiated. Males did not interact with non-receptive females and there were no recorded attempts at infanticide. Male-male interactions were agonistic in the presence of receptive females and neutral at other times. No ritualized displays of dominance and subordinance were seen. The significance of these observations for male reproductive strategies is discussed.

Genital signalling and the coexistence of male vervet monkeys (Cercopithecus aethiops pygerythrus)

To ascertain the social significance of male genital colouration two troops of vervets, one free-ranging and one caged, were observed. It was found that genital signals were associated with intermale agonism. It is suggested that this communicatory system regulates the behaviour of competitors and may thereby have facilitated the evolution of a multimale social system.

Observations on the Inter-troop movement of adult vervet monkeys (Cercopithecus aethiops)

Vervet troops are not closed units and migration - both into and out of the troop - occurs regularly. Available data suggest that it is a male phenomenon related to the accessibility of adult females. The process and its implications are discussed.