Diet Overlap and Polyspecific Associations of Red Colobus and Diana Monkeys in the Taï National Park,Ivory Coast

One possible explanation for the occurrence of the frequent associations between red colobus monkeys and Diana monkeys we observed in Taï National Park, Ivory Coast, is that the two species meet by chance at commonly used food patches. An analysis of the overlap of diets showed, however, that foraging in the same trees could only explain a fraction of the total time in association. Therefore two functional explanations are considered: improvement of foraging efficiency and reduction of mortality due to predation. We did not find any evidence for an improved access to food sources. We conclude that, by default, the predation hypothesis provides the most plausible explanation.     

Socioecology,predation, and cognition in a community of West African monkeys

The Ivory Coast's Taï Forest is home to a diverse primate fauna, including eight monkey species that interact daily with the environment, each other, and a web of predators. These interactions have led to an array of adaptations, some of which conform to theoretical expectations, and others are at odds with current behavioral ecology models. In this paper, we draw on fifteen years of observations to examine two central issues. First, how do broad trends in diet and resource distribution influence group size and levels of sociality? Second, what mechanisms are used to counter pressures exerted by the predator community? The general picture that emerges is that while the pressure exerted by predators at Taï has led to a host of behavioral and cognitive adaptations, it is food preferences and foraging habits, not predation pressure, that are the main determinants, not only of group size, but also its direct consequences ‐ mating systems and sociality levels.     

How feeding competition determines female chimpanzee gregariousness and ranging in the Taï National Park, Côte d'Ivoire

Socioecological theory suggests that feeding competition shapes female social relationships. Chimpanzees (Pan troglodytes) live in fission–fusion societies that allow them to react flexibly to increased feeding competition by forming smaller foraging parties when food is scarce. In chimpanzees at Gombe and Kibale, female dominance rank can crucially influence feeding competition and reproductive success as high‐ranking females monopolize core areas of relatively high quality, are more gregarious, and have higher body mass and reproductive success than low‐ranking females. Chimpanzee females in Taï National Park do not monopolize core areas; they use the entire territory as do the males of their community and are highly gregarious. Although female chimpanzees in Taï generally exhibit a linear dominance hierarchy benefits of high rank are currently not well understood. We used a multivariate analysis of long‐term data from two Taï chimpanzee communities to test whether high‐ranking females (1) increase gregariousness and (2) minimize their travel costs. We found that high‐ranking females were more gregarious than low‐rankers only when food was scarce. During periods of food scarcity, high rank allowed females to enjoy benefits of gregariousness, while low‐ranking females strongly decreased their gregariousness. High‐ranking females traveled more than low‐ranking females, suggesting that low‐rankers might follow a strategy to minimize energy expenditure. Our results suggest that, in contrast to other chimpanzee populations and depending on the prevailing ecological conditions, female chimpanzees at Taï respond differently to varying levels of feeding competition. Care needs to be taken before generalizing results found in any one chimpanzee population to the species level. Am. J. Primatol. 73:305–313, 2011. © 2010 Wiley‐Liss, Inc.     

Impact of Commercial Hunting on Monkey Populations in the Taï region,Côte d'Ivoire1

We studied the impact of hunting on monkey species in the Taï National Park and adjacent forests in Côte d'Ivoire. The average wild meat consumption per capita per year was assessed from market surveys and interviews. We determined that the amount of primate wild meat being extracted in the Taï National Park and surrounding forests was 249 t in 1999. Hunting pressure was the highest on the larger primate species such as red colobus, Procolobus badius, black and white colobus, Colobus polykomos, and the sooty mangabey, Cercocebus torquatus atys. Estimates of population densities were based on line transect surveys. The maximum annual production of each species was calculated using the Robinson and Redford model (1991) and assuming unhunted conditions. Comparing current harvest levels with the maximum sustainable yield suggests that harvest of red colobus monkeys (Procolobus badius) is sustainable, whereas current off‐take of the black and white colobus (Colobus polykomos), the sooty mangabey (Cercocebus atys), diana monkeys (Cercopithecus diana), and Campbell's monkeys (Cercopithecus campbelli) exceeds sustainability by up to three times.     

Stable nitrogen isotope analysis of dentine serial sections elucidate sex differences in weaning patterns of wild chimpanzees (Pan troglodytes)

Offspring provisioning is one of the most energetically demanding aspects of reproduction for female mammals. Variation in lactation length and weaning strategies between chimpanzees (Pan troglodytes), our closest living relative, and modern human societies have been reported. When and why these changes occurred is frequently debated. Our study used stable nitrogen isotope data of tooth root dentine from wild Western chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d'Ivoire, to quantify weaning in these chimpanzees and explore if infant sex plays a role in maternal investment. We analyzed serial sections of deciduous lateral incisor root dentine from four Taï chimpanzees to establish the δ¹⁵N signal of nursing infants; we then analyzed serial sections of first permanent mandibular molar root dentine from 12 Taï chimpanzees to provide quantitative δ¹⁵N data on weaning in this population. Up to 2 years of age both sexes exhibited dentine δ¹⁵N values ≈2–3‰ higher than adult female Taï chimpanzees, consistent with a nursing signal. Thereafter a steady decrease in δ¹⁵N values consistent with the onset, and progression, of weaning, was visible. Sex differences were also evident, where male δ¹⁵N values decreased at a significantly slower rate compared to females. Confirmation of sex differences in maternal investment among Taï chimpanzees, demonstrates the viability of using isotope analysis to investigate weaning in non‐human primates. Additionally, assuming that behaviors observed in the Taï chimpanzees are illustrative of the ancestral pattern, our results provide a platform to enable the trajectory of weaning in human evolution to be further explored. Am J Phys Anthropol 153:635–642, 2014. © 2013 Wiley Periodicals, Inc.     

Food material properties and mandibular load resistance abilities in large-bodied hominoids

Numerous comparative studies have sought to demonstrate a functional link between feeding behavior, diet, and mandibular form in primates. In lieu of data on the material properties of foods ingested and masticated, many investigators have relied on qualitative dietary classifications such as "folivore" or "frugivore." Here we provide the first analysis of the relationship between jaw form, dietary profiles, and food material properties in large-bodied hominoids. We employed ratios of area moments of inertia and condylar area to estimate moments imposed on the mandible in order to evaluate and compare the relative ability to counter mandibular loads among central Bornean orangutans (Pongo pygmaeus wurmbii), Virunga mountain gorillas (Gorilla beringei beringei), and east African chimpanzees (Pan troglodytes schweinfurthii). We used data on elastic modulus (E) of fruit, fracture toughness (R) of fruit, leaves, and non-fruit, non-leaf vegetation, and derived fragmentation indices ( radicalR/E and radicalER), as proxies for bite force. We generated bending and twisting moments (forcexmoment arm) for various mandibular loading behaviors using food material properties to estimate minimally required bite forces. Based on E and R of foods ingested and masticated, we hypothesized improved resistance to mandibular loads in Pongo p. wurmbii compared to the African apes, and in G. b. beringei compared to Pan t. schweinfurthii. Results reveal that our predictions are borne out only when bite forces are estimated from maximum R of non-fruit, non-leaf vegetation. For all other tissues and material properties results were contrary to our predictions. Importantly, as food material properties change, the moments imposed on the mandible change; this, in turn, alters the entire ratio of relative load resistance to moment. The net effect is that species appear over- or under-designed for the moments imposed on the mandible. Our hypothesis, therefore, is supported only if we accept that maximum R of these vegetative tissues represents the relevant mechanical property influencing the magnitude of neuromuscular activity, food fragmentation, and mandibular morphology. A general implication is that reliable estimates of average and maximum bite forces from food material properties require that the full range of tissues masticated be tested. Synthesizing data on ingestive and masticatory behaviors, the number of chewing cycles associated with a given food, and food mechanical properties, should inform the broader question of which foods and feeding behaviors are most influential on the mandibular loading environment.     

Sooty mangabeys scavenge on nuts cracked by chimpanzees and red river hogs—An investigation of inter‐specific interactions around tropical nut trees

Carrion scavenging is a well‐studied phenomenon, but virtually nothing is known about scavenging on plant material, especially on remnants of cracked nuts. Just like meat, the insides of hard‐shelled nuts are high in energetic value, and both foods are difficult to acquire. In the Taï forest, chimpanzees (Pan troglodytes) and red river hogs (Potamochoerus porcus) crack nuts by using tools or strong jaws, respectively. In this study, previously collected non‐invasive camera trap data were used to investigate scavenging by sooty mangabeys (Cercocebus atys), two species of Guinea fowl (Agelestres meleagrides; Guttera verreauxi), and squirrels (Scrunidae spp.) on the nut remnants cracked by chimpanzees and red river hogs. We investigated how scavengers located nut remnants, by analyzing their visiting behavior in relation to known nut‐cracking events. Furthermore, since mangabeys are infrequently preyed upon by chimpanzees, we investigated whether they perceive an increase in predation risk when approaching nut remnants. In total, 190 nut‐cracking events were observed in four different areas of Taï National Park, Ivory Coast. We could confirm that mangabeys scavenged on the nuts cracked by chimpanzees and hogs and that this enabled them to access food source that would not be accessible otherwise. We furthermore found that mangabeys, but not the other species, were more likely to visit nut‐cracking sites after nut‐cracking activities than before, and discuss the potential strategies that the monkeys could have used to locate nut remnants. In addition, mangabeys showed elevated levels of vigilance at the chimpanzee nut‐cracking sites compared with other foraging sites, suggesting that they perceived elevated danger at these sites. Scavenging on remnants of cracked nuts is a hitherto understudied type of foraging behavior that could be widespread in nature and increases the complexity of community ecology in tropical rainforests.     

Can the Patterns of Sexual Swelling Cycles in Female Taï Chimpanzees be Explained by the Cost-of-Sexual-Attraction Hypothesis?

Chimpanzee females of East and West African populations differ in the average number of cycles per interbirth interval. Whereas females in Gombe, Mahale, and Kibale (eastern chimpanzees, Pan troglodytes schweinfurthii) average <9 cycles before they conceive, females at Taï (western chimpanzees; Pan troglodytes verus) average 29 cycles. We examined data from 2 different study groups (North and South) at Taï. By showing that Taï females interrupt cyclic activity for, on average, 7.4 mo between the end of the postpartum amenorrhea period (PPA) and the subsequent conception, and by calculating the number of cycles to conception based on a probability distribution of cycles over the interbirth interval, we show that Taï females average 19.4 cycles (North Group) and 11.7 cycles (South Group) to conception; therefore, the earlier calculation of 29 cycles was an overestimate. Further, at Taï young parous females have a significantly shorter PPA than those of older females, but the number of cycles to conception does not differ significantly between primiparous and nulliparous females. Some of our results are therefore not in line with the predictions of the cost-of-sexual-attraction hypothesis, which proposes that the factor ultimately responsible for the intensity of female sexual attractiveness is female intragroup scramble competition. We discuss an alternative hypothesis—the social passport hypothesis—which is compatible with the results of the study.     

Morphological variation in adult chimpanzees (Pan troglodytes verus) of the Taï National Park, Côte d'Ivoire

Twenty five adult chimpanzee skeletons (Pan troglodytes verus) of known age and sex (15 females, 10 males) from a long‐term study site in Taï National Park, Cote d'Ivoire present new data on variation. These skeletons provide a rare opportunity to measure the cranium and postcranium from the same individuals. We compare measurements and indices of the Taï sample with those of relatively complete Pan troglodytes schweinfurthii skeletons from Gombe National Park, Tanzania. Measurements of Pan paniscus are included as an outside comparison. The Taï and Gombe samples are analyzed by sex; combined sex samples are compared between the two groups, and the two sexes to each other. Taï females and males do not differ in most long bone lengths or in pelvic dimensions, but do differ significantly in cranial capacity, facial measurements, clavicle length, scapular breadth, and femur length. Gombe females and males differ significantly in some facial measurements and in scapular breadth. In combined sex samples, Taï individuals have lower cranial capacity, longer palate and mandible, and greater dimensions in the trunk and limb lengths. Taï females account for most of the variation; males differ from each other only in greater length of humerus and femur. The Taï skeletons provide new data for assessing individual variation and sexual dimorphism within and between populations and species. The combination of cranial and postcranial data provides a clearer picture of chimpanzee intraspecific and interspecific variation than can be gained from either data set alone. Am J Phys Anthropol, 2008. © 2007 Wiley‐Liss, Inc.     

Ecological Partitioning of Cercopithecus campbelli, C. petaurista, and C. diana in the Taï Forest

I determined the degree of ecological partitioning among 3 species of guenons (Cercopithecus campbelli, C. petaurista, and C. diana) in the Taï Forest, Côte d’Ivoire and used the partitioning data to understand competitive relationships among them. Over a 13-mo period, I measured ecological partitioning in terms of food and canopy stratum use for 2 habituated groups of each guenon species and also collected data on food availability. I found that the study species diverged primarily in food items consumed and vertical strata occupied. Cercopithecus petaurista ate much more foliage than the other species did and used mostly the middle strata (5–20 m). Cercopithecus diana ate primarily fruit and used mostly the upper strata (>20 m). Cercopithecus campbelli ate mostly fruit together with large amounts of animal matter and primarily occupied the ground and low strata (<5 m). Of the specific pairs, the diets of Cercopithecus campbelli/C. diana overlapped the most overall and decreased during the season of low fruit availability. Cercopithecus campbelli and C. diana age/sex classes also overlapped more than the age/sex classes of other species pairs. The results suggest that the potential for competition was more intense for Cercopithecus campbelli/C.diana relations than it is for other species pairs. I compare my results from Taï with those from other primate and guenon communities and demonstrate that dietary overlaps and seasonal dietary divergence are lower in Taï than in most other guenon communities.     

Effect of bone strain on cortical bone structure in macaques (Macaca mulatta)

It has recently been shown that the consistency of food significantly affects levels of bone strain in the mandible during mastication (Hylander, '79a). Mandibular bone histology was examined to test the effects of a diet of hard food compared to a diet of soft food in two group of monkeys. One group of rhesus macaques (Macaca mulatta) was fed a diet of commercially prepared hard biscuits. The second group was fed a soft diet the consistency of fudge. Both diets were nutritionally adequate for normal growth and development. As a control for other factors influencing cortical bone structure, fibular morphology was also examined. At the end of the test period, mandibular and fibular tissue samples from the two groups were prepared to determine the amount of secondary Haversian bone present. Mandibular depth at M₂ and fibular anteroposterior diameter were also measured and compared between the two dietary groups. The soft-diet monkeys showed low levels of remodeling in their mandibles. There were large patches of unremodeled bone and resorption spaces were common. The hard-diet monkeys exhibited more extensive evidence of secondary Haversian remodeling in their mandibles. The hard-diet monkeys also had deeper mandibles. In contrast, the fibulae from the two groups had similar mean diameters and showed comparable levels of secondary remodeling. We infer that the higher mandibular bone remodeling levels in the hard-diet monkeys represent an adaptive response to remove and replace fatigued mandibular bone due to higher stress levels associated with the ingestion and mastication of hard foods. We also infer that greater depth of the mandible at M₂ found in the harddiet group represents an adaptive response to higher stress levels associated with the ingestion and mastication of hard foods.     

Dyadic associations of red Colobus and diana monkey groups in the Taï National Park, Ivory Coast

Members of the genus Colobus have been observed to associate frequently with Cercopithecus monkeys in several African sites. In the Taï National Park, Ivory Coast, one group of western red colobus was found to be in association with one particular group of diana monkeys more than could be expected by chance (Holenweg et al., 1996). We show that dyadic association is not an idiosyncrasy of these two groups, but rather a pattern that is general for our study site. All five red colobus groups we studied were closely associated with diana monkeys during more than 60% of the time. Four groups had one particular diana partner group, the fifth two different partners. Apart from the red colobus, three more primate species, the olive colobus, Campbell's monkey, and the lesser spot-nosed monkey, were also strongly attracted to diana monkeys.     

Feeding,Diet, and Jaw Form in West African Colobus and Procolobus

The functional link between mandibular morphology and masticatory stress has been documented by both experimental and comparative investigation. Somewhat more tenuous is the purported connection between dietary variation and the form of the jaws in primates. Several factors complicate the inference of such a connection, including anecdotal or incomplete dietary data from field studies and allometric effects on skeletal form that may have little to do with diet per se. We compared the jaws of sympatric colobines from West Africa to test the effect of diet on mandibular form. Procolobus badius and Colobus polykomos occupy the same habitat yet differ in diet primarily due to the exploitation of hard seeds by C. polykomos. The fact that the two taxa are comparable in body size also obviates the need for allometric qualifications. Colobus polykomos is expected to possess more robust mandibular corpora than Procolobus badius. In fact, the jaws of Colobus polykomos do not differ consistently from those of Procolobus badius in terms of biomechanical function. This apparent failure of mandibular morphology to reflect differences in diet and feeding behavior may be due to a variety of factors. We suspect that functional demands related to canine tooth support are contributing to obliteration of the expected biomechanical signal. Successful prediction of dietary effects on mandibular form requires consideration of competing structural and functional demands. The influence of diet on mandibular corporeal morphology is not equivalent across different primate species.     

Buttress drumming by wild chimpanzees: Temporal patterning, phrase integration into loud calls, and preliminary evidence for individual distinctiveness

Wild chimpanzees (Pan troglodytes) generate low-frequency sounds that are audible to humans from a distance of at least 1 km away by hitting the buttresses of trees with their hands and feet. This buttress drumming occurs in discrete bouts of rapidly delivered beats that usually accompany “pant hoots,” the species-specific long-distance vocalization. Individual differences in male chimpanzee (P.t. verus) drumming were investigated during a 6-month field study in the Taï National Park, Ivory Coast. Analysis of drumming bouts recorded from six adult males revealed significant differences between individuals in three acoustic features: (1) mean duration of inter-beat interval; (2) mean number of beats per bout; and (3) mean bout duration. Preliminary analysis indicated that individuals differ in their tendency to deliver drum beats in temporally close pairs separated by longer interbeat intervals. Qualitative examination also suggested that individuals may differ in the temporal integration of drumming into the pant hoot vocalization. These results suggest that there may be acoustic cues available for chimpanzees to recognize unseen males by their drumming performances alone. Drumming by Taï chimpanzees was also compared to drumming by chimpanzees (P.t. schweinfurthii) from the Kanyawara study group in Kibale National Park. Uganda. The Kanyawara chimpanzees appeared to drum more often without vocalizing than did the Taï chimpanzees. When they did drum and vocalize together, the Kanyawara chimpanzees appeared to integrate their drumming later into the associated pant hoots than did the Taï chimpanzees. These results suggest the possibility that interpopulation variation exists in chimpanzee buttress drumming.     

Cooperative hunting roles among taï chimpanzees

All known chimpanzee populations have been observed to hunt small mammals for meat. Detailed observations have shown, however, that hunting strategies differ considerably between populations, with some merely collecting prey that happens to pass by while others hunt in coordinated groups to chase fast-moving prey. Of all known populations, Taï chimpanzees exhibit the highest level of cooperation when hunting. Some of the group hunting roles require elaborate coordination with other hunters as well as precise anticipation of the movements of the prey. The meat-sharing rules observed in this community guarantee the largest share of the meat to hunters who perform the most important roles leading to a capture. The learning time of such hunting roles is sometimes especially long. Taï chimpanzee males begin hunting monkeys at about age 10. The hunters’ progress in learning the more sophisticated hunting roles is clearly correlated with age; only after 20 years of practice are they able to perform them reliably. This lengthy learning period has also been shown in some hunter-gatherer societies and confirms the special challenge that hunting represents.     

青木川自然保护区川金丝猴食性的季节性变化

2005 ～2008 年于陕西省青木川自然保护区使用瞬时扫描法观察了川金丝猴的食性。结果表明,川金丝猴冬季和夏季共取食42 种植物,可鉴定植物归属23 科34 属。川金丝猴食物类型包括果实、花、树叶、树皮、树芽。夏季取食21 种植物的果实或树叶;冬季取食25 种植物。树叶是其冬季主要食物,取食频次占总取食频次的73.0% ;夏季取食果实的频次占总取食频次的72.2% ,灯台树果实是其主要食物。啃食树皮行为主要发生在落叶阔叶林、针叶林与落叶阔叶混交林;在常绿和落叶阔叶混交林中,树皮啃食强度则相对较小。与其它地区金丝猴的食性比较,该地区川金丝猴食物谱较宽。蔷薇科和壳斗科植物在川金丝猴食物组成中最多,杨柳科、桦木科、山茱萸科、槭树科和忍冬科植物也取食较多。