Browsing by Author "Henzi, S. Peter."

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Developing a methodology for cognitive research with socially-housed chacma baboons.
(2004) McFall, Andrew.; Henzi, S. Peter.; Barrett, Louise.
Testing on laboratory-housed primates has long been the standard for research in cognitive psychology and other areas. As an alternative to this, a group of socially housed chacma baboons (Papio hamadrayas ursinus) at the Centre for Animal Rehabilitation and Education near Phalaborwa in Limpopo Province, South Africa, were the subjects for a set of basic cognitive tests. The purpose of the tests was to explore the importance of analogical reasoning by means of testing perceptual and conceptual skills in baboons. The main aim of this research is to investigate the degree to which captive but socially housed baboons are useful as experimental subjects, and to develop an apparatus and protocol to perform these tests in situ in the baboons' home cages. Five baboons were chosen as the subjects for experimentation. All subjects completed three groups of tasks to a criterion of at least 80% success over four successive experiments. The tasks tested baboons' discrimination ability between two coloured tiles, a reversal of that same discrimination task, and a simple match to- sample task. As a result of time constraints, further tasks testing conceptual ability had to be abandoned. A record was kept of environmental and social factors that may have influenced the motivation of the subjects. The time taken to complete each experiment correlated in many cases with the number of distractions experienced by the subjects. There appeared to be no significant correlation between the score attained by a subject and the number of distractions experienced by that subject. The greater number of distractions experienced by the subjects was a result of the more engaged social world in which these baboons exist. Consequently, their motivation to perform repetitive cognitive tests was decreased, and needed to be countered in novel ways. An apparatus and a protocol for testing under these conditions were developed. Testing baboons' cognitive skills in these circumstances is both possible and desirable for ethical reasons, though the process takes longer than under laboratory conditions.
The developmental behavioural ecology of infant baboons (Papio cynocephalus ursinus)
(1994) Lycett, John Edward.; Henzi, S. Peter.
Presented in this thesis are the results of a 23-month field study (April 1991 - February 1993) which focused on infant development in a free-ranging baboon troop (Papio cynocephalus ursinus) inhabiting the Cathedral Peak Reserve in the Drakensberg Mountains, Natal Province (South Africa). The troop selected for study was, in demographic composition, representative of the greater Drakensberg baboon population. During the course of the study, five infants were born into the troop. At the end of the data collection period, the infants ranged in age from II-months to 17 -months old. The data presented are extracted primarily from 2678 half-hourly scan samples, representing approximately 1340 hours of observation. Data presented in this study indicate that baboon births in the Drakensberg are seasonally timed such that mothers are afforded some measure of relief from the energetic costs associated with intense infant dependency, particularly during the first few months postpartum. However, the timing of births is not optimal in terms of the development of infant nutritional independence. This has implications for the interbirth interval (38.4 months) which, for the Drakensberg females, is substantially longer than that for comparative studies, while the rate of infant survivorship through to 12-months (95%) is considerably higher than for other baboon populations. The development of independent feeding for the Drakensberg infants is, when compared with infants from other studies, considerably slower. The delayed transition to independent feeding which was observed is explained with reference to seasonally variable ecological conditions in the Drakensberg which necessarily resulted in infants remaining nutritionally dependent on mothers for a longer time than would normally be expected. The relationship between dependent and independent feeding, as alternate infant strategies, is considered within the context of weaning and its role in the iv promotion of independence. A model which purports to delineate the weaning period with reference to the rate of decline in various measures of maternal investment is applied to the data for this study, as well as for comparative studies. No clear consistency is evident in the rate of decline across the various measures for the present study. The trajectories of infant behavioural development toward the adult model of independent activity are described and considered. With the exception of nutritional independence, all other trajectories of infant behaviour followed similar developmental patterns to infants in comparative studies. Thus the appearance of particular behaviours, and the age at which transitions to independence were made, confirmed a general baboon pattern. The implications and consequences of delayed feeding independence for changes in behavioural development are considered within the context of general activity budgets. Data are also presented which examine the contexts within which adult males interact with infants. These data are considered in relation to the possible functional purposes served by male interaction with infants, as well as in terms of the effect male interaction with infants has on inter-male interaction. The data indicate individual male variability in both the extent and contexts of interaction with infants.
The dynamics of social relationships among female Chacma baboons (Papio cynocephalus ursinus) in Zululand.
(1993) Ron, Tamar.; Henzi, S. Peter.
The focus of this study is the effect of environmental conditions on the social relationships among females in a free-ranging troop of chacma baboons (Papio cynocephalus ursinus), in a southern woodland habitat. The female dominance hierarchy, rank related differential costs and benefits to individuals, and the nature of special relationships between females, were followed. The study was conducted for a total of 18 months during three years, at Mkuzi Game Reserve, Zululand, South-Africa. The study troop occupy a rich woodland habitat with abundant food resources. Visibility under these conditions is poor and the baboons are subjected to leopard predation. Intra-troop competition for food among female primates and its effect on lifetime reproductive success, has been widely stressed to be a major cost for low ranking females. No evidence of competition for food was found among females at Mkuzi. It is suggested that the main cause for mortality may be predation by leopards, and that females compete mainly over a safe spatial position. The following characteristics of female sociality at Mkuzi may support this suggestion: 1. While no indication of rank related feeding behaviour, reproductive success, or 'attractiveness' to others was found, the higher ranking females had more access to central, and thus better protected, spatial positions in the troop. 2. The importance of social associations among females at Mkuzi seems to lie in mutual grooming and protection from predation by the vicinity to each other, and not in coalitionary support. Female associates were thus not necessarily adjacent ranking and probably not kin. 3. Although female dominance hierarchy was usually stable, the lowest ranking adult female has promoted her rank independently, following the disappearance of her only female associate and during her pregnancy, when she was probably subjected to high risk of predation. 4. Following troop fission, most females chose to improve their own rank position by adopting the AYS strategy (Abandon Your immediate Superior in rank), rather than joining associates. It is suggested that the resident males were responsible for the initiation of troop fission, in order to decrease the high cost of sexual competition to them, by reducing the number of males in each daughter troop. High intensity of competition between males was the result of the high female reproductive success. Risk of predation, and therefore the cost to individual females, increased after fission. This study may present an additional accumulating behavioural evidence on adaptations environmental conditions. the of flexibility primates example to of social and to various environmental conditions.
Host suitability in the Diderik cuckoo Chrysococcyx caprius - ploceid brood parasitism breeding system.
(2003) Lemos, Sharon A. C.; Lawes, Michael John.; Henzi, S. Peter.
Host suitability is critically important to the success of brood parasitism. Parasites must select a host that not only accepts its egg but also is capable of successfully rearing the parasite to fledging. Nearly all brood-parasites appear to avoid low-quality hosts that are likely to reject their eggs, that are of inappropriate size, or that feed their nestlings nutritionally inadequate or insufficient food. The diderik cuckoo, (Chrysococcyx caprius), is an obligate brood parasite known to parasitise a wide spectrum of ploceids, including the yellow weaver (Ploceus subaureus) and the southern red bishop (Euplectes orix). Theory predicts that brood parasites should exploit insectivorous passerines of similar adult size to themselves that provision large quantities of high protein food to their young. However, the relatively smaller granivorous red bishop is the most heavily parasitised host species of the diderik cuckoo in southern Africa. To investigate why an apparently unsuitable host species was so heavily parasitized several populations of parasitised red bishops and yellow weavers (omnivores) were studied in the Pietermaritzburg region, KwaZulu-Natal, South Africa. Host suitability was assessed by examining diet quality, host-provisioning rates, cuckoo nestling growth and cuckoo fledging success. Diderik cuckoo nestlings were provisioned the same diet as the host nestlings in red bishop and yellow weaver nests. However, cuckoos in bishop nests received a protein-deficient seed diet from as early as six days following hatching. In contrast, weaver-cuckoo faeces contained 1~ times more insect than their bishop counterparts throughout their nestling period. Provisioning rates by bishop females were significantly slower than by yellow weavers, and neither bishop nor weaver hosts showed any 'supernormal' effort when feeding a young cuckoo. Both host species provisioned cuckoo nestlings at a similar rate and with a similar food mass as their own nestlings. Diderik cuckoos in bishop nests grew at a slower rate and fledged in a poorer condition than their yellow weaver counterparts. Red bishops are likely the most exploited host of the diderik cuckoo because i) cuckoo eggs are more readily accepted by the less discriminating bishop and ii) the bishop-breeding season coincides more closely with that ofthe diderik cuckoo than the yellow weaver. Thus, diderik cuckoos may preferentially exploit bishop hosts because of the low frequency of cuckoo egg rejection, which ultimately results in many cuckoos fledging from bishop nests despite the lowquality diet provisioned and 53% (n = 53) fledging success in nests of this species. In the yellow weaver system, the protein-rich diet and the greater probability of cuckoo nestling survival (80%, n = 5) may compensate for the high rejection rate of cuckoo eggs by this host. Thus, both host systems seem to represent evolutionary compromises for the diderik cuckoo, with neither red bishops nor yellow weavers being entirely ideal as host species.
Human social values : explorations from an evolutionary psychology perspective.
(1999) Moomal, Zubair.; Henzi, S. Peter.
The series of papers in this dissertation are aimed at testing evolutionary hypotheses concerning the adaptive advantages of religious values or experiences, a gender difference in purpose in life and the evolutionary relationship between deception and self-deception. Explanations are argued for in terms of their consequences for evolutionary fitness contributing to individual survival within the human species. Darwin's theory of natural selection within the framework of evolutionary psychology provides the theoretical background for the study. In psychology as well as in other social sciences, Darwinian theories of natural and sexual selection have been undergoing a revival with a significant upsurge of an interest in evolutionary psychology as a unifying paradigm for the understanding of human functioning as a living organism, optimising its fitness to survive the exigencies of environmental and social selection pressures. The broad or covering hypothesis addressed is that religious values or experiences, purpose in life, deception and self-deception each involve a kind of consciousness or strategic cognitive process that has evolved through the operation of natural selection due to its importance and worth for the survival of the individual. The study is empirical, conducted by using the technique of secondary analysis on the data yielded by the World Values Survey collected in 43 countries in its second wave of 1990 to 1993 as well as on a South African dataset containing variables of interest to the second and third papers of this dissertation. National aggregate data has been obtained from the United Nations Development Reports for the corresponding years under study. Findings showed a significantly positive relationship between religious values and evolutionary fitness promoting factors derived by factor analysis; a significantly greater purpose in life in females as compared to males; and a significantly positive relationship between deception and self-deception. However, the relationship between deception and evolutionary fitness promoting factors, derived by factor analysis, was inconclusive.
The socioecology and conservation of the Samango monkey (Cercopithecus mitis erythrarchus) in Natal.
(1990) Lawes, Michael John.; Perrin, Michael Richard.; Henzi, S. Peter.
The samango monkey (Cercopithecus mitis erythrarchus) is the southern most representative of the polytypic mitis group. The samango is also the only truly arboreal guenon to have radiated as far as 30°S. At southern latitudes a greater seasonality of climate and an attendant seasonal shift in food availability is expected to restrict the foraging strategy of the arboreal guenon. In the absence of arboreal congenerics and few frugivorous bird and bat species, the samango experiences a level of competitive release at Cape Vidal not found in other equatorially located mitis populations. In this thesis I examine and contrast the diet and feeding behaviour of the mitis species group. In this way I illustrate the consequences of seasonality of food abundance and competitive release on the foraging strategy of the samango, and provide an explanation for the unique distribution of the samango monkey as the only arboreal guenon in southern Africa. Despite seasonality in climate and abundance of food resources, my data show that, in general, samango monkeys at Cape Vidal are not food limited. For this reason Cape Vidal samangos have large troop sizes (25+), use small home ranges (15 ha) and have the highest density (2.02 ind/ha) of any C. mitis population researched to date. Fruit forms an important part of the diet year-round and therefore, energy and carbohydrate are abundant. There is very little intra-group aggression for food, although interindividual distances are greatest when feeding. There are age-sex differences in the diet, and adult males eat more fruit while females eat more leaves than other age-sex classes. The most important aspect of the feeding strategy of the samango is concerned with obtaining adequate protein in the diet, and throughout the range of the mitis group, populations differ most in feeding strategies used to secure protein-rich foods, such as young leaves, flowers and invertebrates. In this respect seasonal nutrient (protein) availability, rather than seasonality of food abundance per se, is the most limiting component of the forest environment. Unlike equatorial populations of mitis that derive most of their protein from insects, samangos are unable to adopt a similar strategy. Insects were available to the monkeys, and then only in low numbers, in the wet summer season at Cape Vidal. Samango monkeys, therefore, make greater use of a wider variety of plant items for protein acquisition. During the wet summer months, insects, flowers and young leaves are used by samangos to obtain sufficient protein for important reproductive activities, such as lactation, and initial growth of the infant. During the drier winter months only mature leaves and small quantities of young leaves are available as protein resources, consequently samangos use more mature leaf in the diet than other C. mitis populations. Adaptations of the gut and specialized gut microflora permit this high degree of folivory in the diet (Bruorton and Perrin 1988) of the samango monkey. This is a characteristic that does not appear to be shared with other arboreal guenons. In so far as protein is essential for reproduction, folivory in c. mitis has been important in permitting this arboreal guenon species-group to radiate into southern latitudes where protein is more seasonally available. The ability of samango monkeys to eat large quantities of leaves at anyone time, accounts for their unique position as the only arboreal guenon species in southern Africa.
Some aspects of visual signalling and social organization in the vervet monkey (Cercopithecus aethiops pygerythrus).
(1982) Henzi, S. Peter.
This study uses data from three free-ranging and one caged troop to describe the visual signals identified in the South African subspecies of vervet monkey (Cercopithecus aethiops pygerythrus) and to then compare them to those seen at other localities and in other species. It further assesses some signals used specifically by adult males - those involving secondary sexual characters - in terms of male social strategies. In the pursuance of this four aspects of the literature were reviewed in detail. It is concluded that: 1. Natal vervets use fewer visual signals that do other species living in more open habitat. These signals are, however, very similar to those recorded in East Africa, while differing more from those isolated in the West African representitive of the vervet group. 2. Vervet troops are not closed units and migration - both into and out of the troop - occurs frequently. The data suggest that it is a male phenomenon related to the availability of females. 3. The signalling function of the genitals does not accord with that ascribed to them by Wickler (1967). Penile extensions are closely associated with aggressive behaviour by the signaller, and scrotal retractions with submissive behaviour. Associated with these structures are displays that facilitate their presentation to the recipients. 4. While males yawn more than any other age-sex class, largely for social and not physiological reasons, there is no clear evidence that yawns serve specifically to display the canines. Nevertheless, by being strongly associated with certain interactions they are presumed to accrue signal value. 5. As males move into troops where they must compete with unrelated males for the same resources, it is concluded that the genital signalling system has evolved to mediate male relationships. This is of special significance as the "multimale" system of vervets is regarded as being less developed than those of Papio or Macaca monkeys.
The use of neuroimaging in the assessment of brain size and social structure in odontocetes.
(1996) Tschudin, Alain Jean-Paul Charles.; Peddemors, Victor Marten.; Henzi, S. Peter.; Royston, D.
This study successfully utilised the non-invasive neuroimaging techniques of Computerised Tomography (CT) and Magnetic Resonance Imaging (MRI) to establish that dolphins have high relative brain size values, transcending the primate range for neocortex volume and neocortex ratio. Bottlenose dolphins superseded human values of the neocortex ratio and common dolphins marked the upper limit of the range for the dolphin species under investigation. In addition this study was the first to find a correlation between sociality and neocortex ratio in dolphins (R.I.M. Dunbar, pers.comm), which supports the hypothesis of neocortical development in relation to sociality/group size (Sawaguchi & Kudo 1990; Dunbar 1992) and social/Machiavellian intelligence (Byrne & Whiten 1988; Byrne 1995). The study devised new measures of relative brain size, including the grey-white matter and higher cortical ratios and these require further research before verification of their efficacy. Equations were calculated to allow estimation of: (1) MRI values of total brain volumes from CT values, (2) total brain volume from cranial volume using CT, (3) cerebral cortex volume from cranial or total brain volume (CT) and (4) cerebral cortex and cerebellar cortex volume from total brain volume (MRI). The effects of freezing and defrosting on volume and density of CT and MRI values were investigated. Additionally, the relationship between relative brain size (EQ) and sociality was investigated for other dolphin research, using previously published figures, but no significant correlations were found. Finally, dolphin values were compared to primate values for neocortex volume and neocortex ratio with the finding that the only primate within the dolphin range of neocortex was the human, positioned higher than the solitary humpback dolphin, but below all of the other, more socially complex, dolphin species.