Time budget of the green monkey,Cercopithecus sabaeus: Some optimal strategies

Members of a single group of green monkeys spent, on average, 44.8% of their waking time foraging, 46.7% resting, and 8.5% in social activities, over 1 year. There was significant variation in activity budgets over months (ranging from 35 to 55% of the time spent feeding). Diurnal rhythms of feeding and ranging were influenced by the daily cycle of temperature in predictable ways in different seasons: in the dry season, activity was reduced if it was too hot or too cold, while the temperature in the wet season did not affect activities. Feeding was also synchronized among individuals on a finer time scale, irrespective of the time of day. There was closer synchrony when feeding on less common foods. An ecological model of foraging time and energetics was tested, using estimates of the costs and benefits of foraging and predicting how these are optimally balanced in relation to the food density. Both feeding time and distance traveled increased as food availability increased. Costs and benefits were balanced over several days. Comparisons between populations of Cercopithecus aethiopswere made; differences in time budgets were compared with differences in the availability and quality of food. Insufficient comparative data are available for firm conclusions about the role of different energetic and nutritive strategies in population differences.     

Wide-ranging chimpanzees at Mt. Assirik,Senegal

A 4-year study of the ecology and ethology of wild chimpanzees (Pan troglodytes verus)was carried out in far western Africa. Contacts with chimpanzees and the locations of their nests were noted to determine which types of habitat were most used and to estimate the density of the population and the size of its home range. The results show that this community has one of the lowest densities and largest home ranges of all populations of chimpanzees studied so far. As such, it may provide a useful model for the reconstruction of hominid evolution in the Plio-Pleistocene.     

Life-history characteristics of a wild population of vervets (Cercopithecus aethiops sabaeus) in Barbados,West Indies

Life history data are presented for a population of vervets, Cercopithecusaethiops sabaeus, in Barbados, West Indies. The data were obtained from two habituated troops and from vervets captured during a large-scale trapping program. Individuals of known age from one troop were weighed periodically, and separate growth curves generated for males and females. The mean weight of captured adult females was 3.3 kg; that of adult males, 5.3 kg. The average age at sexual maturity is estimated at 34 months for females and 60 months for males. Vervets give birth throughout the year, but most infants are born between April and July. The average interbirth interval following a surviving infant is 11.8 months. The mortality of juveniles is heaviest between birth and 2 years of age and decreases thereafter. Males emigrate from their natal troops at sexual maturity and one incident of a juvenile female emigrating is reported.     

Observations on the ecology and social organization of the green monkey,Cercopithecus sabaeus,in Senegal

The green monkey,Cercopithecus sabaeus, has not been studied in its natural habitat in West Africa. This paper reports observations made during a 3-month study in Senegal. Green monkeys live in multimale groups averaging some 12 individuals. Information is given on home range size, use of habitat, daily activity patterns, diet and birth seasonality. Social organization is discussed and data are given on the relationships between age-sex classes, aggression and leadership. Inter-group relations are discussed and it is suggested that groups defend their ranges as territories. The ecology and social organization of green monkeys is compared with that of populations ofC. aethiops studied in East Africa and they are found to be similar.     

The application of biomechanical motion analysis to aspects of green monkey (Cercopithecus a. sabaeus) locomotion

A cinematographic method of biomechanical motion analysis is presented which permits the determination of body segment forces and joint moments of force, and thereby dominant muscle action. An analysis of the horizontal leap of Cercopithecus is used as an example of the utility of this approach in the area of functional morphology. Kinematic and kinetic data are presented and discussed in terms of the biomechanical requirements of this form of locomotion. The importance of a consideration of inertial as well as gravitational forces in an analysis of positional behavior involving body motion is stressed.     

New observations on the tool-behavior of chimpanzees from Mt. Assirik (Senegal,West Africa)

The tool-behavior of chimpanzees were studied at the Mt. Assirik, in the Parc National du Niokolo-Koba, Senegal from December 1982 to June 1983 and from February 1985 to January 1986. Five leaf-stalks to obtain termites ofMacrotermes subhyalinus species and four sticks to obtain honey (this is the first report on the use of tools to obtain honey by wild chimpanzees in far western Africa) were found; we also report the first evidence of tools probably used as hammers to break open hard-shelled fruits ofAdansonia digitata. We conclude that Mt. Assirik chimpanzees provide evidence of a certain cultural behavior related to the use of stones.     

Frequent insectivory by two guenons (Cercopithecus lhoesti and Cercopithecus mitis) in the Kalinzu Forest, Uganda

I investigated the feeding ecology of lHoests monkeys (Cercopithecus lhoesti) and blue monkeys (Cercopithecus mitis) in the Kalinzu Forest, Uganda. Although forest guenons are generally thought to be frugivores or folivores, these two guenons spent a large proportion of their time feeding on invertebrates. The lHoests monkey and the blue monkey spent as much as 66 and 50% of their time on insectivory, respectively. These proportions of time spent on invertebrate feeding are higher than those reported elsewhere for forest guenons. LHoests monkeys mainly utilized the area near the ground for invertebrate feeding, while blue monkeys utilized the area around 20 m above the ground. It seemed that guenons have an ability to change their diet according to the environment.     

Optimal foraging and intraspecific diet differences in the lizard Cnemidophorus sexlineatus

Summary Previous studies have shown that adult and juvenile six-lined racerunners, Cnemidophorus sexlineatus, consume different sizes and taxa of arthropod prey. the purpose of this study was to determine if these differences could be explained in terms of energy cost and benefit parameters as related by the optimal diet model. Handling times and encounter rates with each of five categories of prey were determined by direct observation of lizard foraging behavior in the field. Energetic cost of search and energy content of prey were estimated from data in the literature. Mean values of all these parameters were used in the classic optimal diet model to determine which prey types yield the greatest rate of net energy gain for adult and juvenile racerunners. Grasshopper-like insects were the most valuable prey for adults, whereas plant and ground arthropods were the most valuable prey for juveniles. These findings correspond to the age-class specific diet differences.Each age-class adopts foraging tactics that increase the chance of finding the most valuable prey. Adult racerunners move hastily over a large area to find the relatively rare, but large and mobile grasshopper prey. Juveniles move much more slowly, and carefully investigate twigs and leaves to find smaller, cryptic plant and ground arthropods. However these foraging tactics do not preclude the taking of less valuable prey items, should they be encountered. This is because it is energetically better on average to eat the prey item rather than skipping it to search for better prey, except for the case of juvenile racerunners eating grasshoppers. That juvenile racerunners will attempt to capture and consume even very large grasshoppers is contrary to the expectations derived from the optimal diet model. This behavior may be the result of the foraging rule of thumb racerunners use to find their prey.     

Diet of wild chimpanzees (Pan troglodytes verus) at Mt. Assirik,Senegal: I. Composition

The composition of the diet of a savanna-living population of wild chimpanzees (Pan troglodytes verus) at Mt. Assirik in Senegal is presented. The study site had a prolonged dry season, high temperatures, and vegetation dominated by grasses. Data came from direct observation, fecal specimens, and feeding traces; thus, strict criteria for acceptance of the indirect data were specified. Composition of diet was given in terms of species and family of prey, parts eaten, life-form, type of habitat, and criteria for inclusion. Forty-three species of plants with 60 parts were eaten; mostly fruits, from trees, in woodland. Nine species of animal prey were eaten, mostly social insects. An additional 41 species of plants with 53 parts were classed as likely to be eaten by chimpanzees, mostly on the grounds of their being eaten by sympatric anthropoids. Overall, the diet of the apes at Mt. Assirik resembles that of this species elsewhere in Africa, but the size of the dietary repertoire seems small and the proportion of low-quality foodstuffs high. The latter are mostly time-consuming to collect or tedious to obtain or process, and include underground storage organs.     

A study of the ultrastructure of the small iris vessels in the vervet monkey (Cercopithecus aethiops)

Summary Eyes of vervets were fixed by several methods, and the iris capillaries were studied by electron microscopy. The capillaries have a continuous endothelium without fenestrae. Tight junctions are always present in intercellular clefts of the endothelium, and marginal folds are frequent. A rather thick basement membrane is present, similar to what is found in the human iris. Pericytes are frequent, and specialized areas of membrane contact between endothelium and pericytes are described. Peculiar marginal vacuoles are found in the endothelium after perfusion with hypertonic fixative.     

Within-group differences in captive Diana monkey (Cercopithecus diana diana) behaviour

This case study examines the activity budgets of captive Diana monkeys (Cercopithecus diana diana) and discusses results in the context of what is known regarding captive and wild-type behaviour in this species and other guenons. The activities of a family group of Diana monkeys (two parents and four offspring) housed at Edinburgh Zoo, UK, were quantified using a 5-min interval scan sampling technique. The 5100 observation points collected showed that the subjects spent the largest proportion of their time observing (approx. 46%), followed by feeding (approx. 15%), playing (approx. 11%), mutual grooming (approx. 8%) and resting (approx. 7%). The daily activity budgets for each of the subjects were tallied and, at the end of the 10-day observation period, used to produce a data matrix consisting of nine behaviour variables per subject. Clear among-individual differences in activity were identified with canonical discriminant function analysis. This multivariate approach illustrated how the combined behaviours of the parent male were distinct from those of the rest of the family group. Within the remainder of the group, the three youngest offspring displayed similar activity budgets, whereas the overall behaviour of the eldest offspring (a female) was between that of its siblings and her mother.     

An electron microscopic study of the permeability of iris capillaries to horseradish peroxidase in the vervet monkey (Cercopithecus aethiops)

Summary Anesthetized vervets were given intravenous injections of horseradish peroxidase. Subsequent studies of iris capillaries with the electron microscope showed peroxidase reaction product within the lumen of the vessels and in endothelial vesicles, but no peroxidase had penetrated the vascular endothelium. The normal ultrastructure of the vascular wall was retained.     

Optimal and central-place foraging theory applied to a desert harvester ant,Pogonomyrmex californicus

Summary Certain predictions of optimal- and central place-foraging theory were tested on the desert harvester ant, Pogonomyrmex californicus. Colonies were offered three different sizes of oat seed and found to maximize net energy intake (ei) over time (t _i ) by harvesting the seed sizes with the highest e _i /t _i rank. Two aspects of t _i were measured that were assumed constant in previous studies. The handling components of t _i (time required to manipulate the seed and travel time back to the colony with the food) were measured and found to be positively correlated with seed size. The manipulation success rate (the percentage of handled seeds successfully picked up) decreased with increased seed size. These results point out how important it is to measure all parameters of e _i /t _i rather than to assume constancy with both prey type and foraging distance. The relative abundance of less preferred food types was important in determining the proportion of preferred types in the diet. The food supply of eight colonies was manipulated experimentally over a 25-day period. Four deprived colonies were constrained within aluminum enclosures to prevented foraging. The remaining four satiated colonies were given food ad libitum. The niche breadths of the treated colonies were then compared to controls, but found not to differ significantly. Seed baits were offered at three distances from the colony to test whether selectivity increased with disance. Contrary to theoretical predictions, all colonies harcested about the same proportion of each seed size at each distance.     

The diet of the olive colobus monkey,Procolobus verus,in Sierra Leone

Observations of the feeding behavior of wild olive colobus monkeys (Procolobus verus)were made in southern Sierra Leone, West Africa. Most data came from systematically sampling one habituated social group, which inhabited old secondary rain forest on Tiwai Island. Olive colobus at Tiwai were highly selective feeders, obtaining most of their food from a small number of uncommon middle-canopy trees, from the forest understory, and from climbers. Mature leaf blades were largely ignored; young foliage (particularly of climbers) was a year-round dietary staple, while seeds, flowers, and mature leaf petioles were seasonally important. It is argued that this diet results largely from selection for two different attributes of food: high digestibility and physical location. Preferred foods had low fiber and tannin contents, while preferred feeding sites were in thick low growth and climber tangles. P. verusis the smallest extant primate species using a foregut fermentation system. Observations of its diet accord with inferences drawn from dental anatomy, digestive physiology, and considerations of body size.     

Optimal foraging theory predicts effects of environmental enrichment in a group of adult golden lion tamarins

The success of environmental enrichment programs in effecting specific changes in the behavior of captive animals has not always been uniform. Separate studies demonstrated both an increase in food competition and a decrease in food competition among captive group-living primates upon introduction of foraging devices. The objectives of this study were to measure the effects of variation in resource distribution and availability on food competition in a group of captive adult golden lion tamarins (Leontopithecus rosalia). The resource variables chosen were suggested from optimal foraging theory. The energy invested to obtain an item influenced food transfer and aggressive behaviors while food abundance did not. All individuals obtained an equivalent number of items over the course of the experiment from the foraging device, even though some tamarins obtained most of their food rewards directly from the device while others received their food rewards primarily through food transfer from other group members. Because the monkeys appeared highly motivated to obtain food from the test apparatus and did not habituate to it, the foraging device used in this experiment could be used as regular environmental enrichment for golden lion tamarins. One way to circumvent potentially unacceptable rates of aggression, with this or any feeding protocol that increases foraging task complexity and search time, may be to provide more than one foraging device per group. Zoo Biol 17:231–244, 1998. © 1998 Wiley-Liss, Inc.     

Ranging behavior ofMacaca thibetana at Mt. Emei,China

Food handouts from visitors to Mt. Emei, in The People’s Republic of China, have considerably increased the diversity of food available to an indigenous population of Macaca thibetana.Some 43% of the feeding time was spent at the trail area frequented by tourists. Ranging behavior was of two kinds: wandering around within the group’s most densely used areas and making peripheral excursions between the areas. Three kinds of trail-area use were observed: three-group overlapping, two-group overlapping, and exclusive. M. thibetanatended to use sheltered sites for sleeping, to ensure safety and/or to keep dry in a rainy habitat. Exclusively and successively used sleeping sites were noted. The average size of the home range per group was 3 km ²; the average population density for the entire range was 13/km², and the biomass was 109 kg/km². The population may be growing, a possibility that is also supported by previous analyses using data on group composition.     

Optimal central-place foraging by beavers: Tree-size selection in relation to defensive chemicals of quaking aspen

Summary At a newly occupied pond, beavers preferentially felled aspen smaller than 7.5 cm in diameter and selected against larger size classes. After one year of cutting, 10% of the aspen had been cut and 14% of the living aspen exhibited the juvenile growth form. A phenolic compound which may act as a deterrent to beavers was found in low concentrations in aspen bark, and there was no significant regression of relative concentration of this compound on tree diameter. At a pond which had been intermittently occupied by beavers for over 20 years, beavers selected against aspen smaller than 4.5 cm in diameter, and selected in favor of aspen larger than 19.5 cm in diameter. After more than 28 years of cutting at this site, 51% of the aspen had been cut and 49% of the living aspen were juvenileform. The phenolic compound was found in significantly higher concentrations in aspen bark than at the newly occupied site, and there was a significant negative regression of relative concentration on tree diameter. The results of this study show that responses to browsing by trees place constraints on the predictive value of standard energy-based optimal foraging models, and limitations on the use of such models. Future models should attempt to account for inducible responses of plants to damage and increases in concentrations of secondary metabolites through time.