Showing papers in "International Journal of Primatology in 2001"

Primate Innovation: Sex, Age and Social Rank Differences

Abstract: Analysis of an exhaustive survey of primate behavior collated from the published literature revealed significant variation in rates of innovation among individuals of different sex, age and social rank. We searched approximately 1,000 articles in four primatology journals, together with other relevant databases, for examples of innovation. The reported incidence of innovation is higher in males and adults, and lower in females and nonadults, than would be expected by chance given the estimated relative proportions of these groups. Amongst chimpanzees, the only species for which there are sufficient data to consider alone, there is a similar sex difference in the propensity to innovate, but no effect of age. Chimpanzees of low social rank are reported as innovators more frequently than high-ranking chimpanzees are. Male chimpanzees innovate more often than females in sexual, courtship, mating and display contexts; that is, in contexts likely to increase access to mates. The largest number of recorded observations are in the foraging context, wherein contrary to expectations, there is no evidence for female chimpanzees exhibiting more innovation than males. The study is the first extensive investigation of behavioral innovation in primates and provides evidence that much individual variation in the propensity to innovate can be explained in terms of sex, age, and social rank.

Semifree-ranging Tufted Capuchins (Cebus apella) Spontaneously Use Tools to Crack Open Nuts

Abstract: Naturalistic studies on tool use by nonhuman primates have focused almost exclusively on Old World monkeys or hominoids We studied the cracking of Syagrus nuts with the aid of stones by a group of semifree-ranging capuchins living in a reforested area (Tiete Ecological Park, Sao Paulo, Brazil) Our data are from direct observation and from mapping nut-cracking site utilization All adults, subadults and juveniles (plus one infant) crack nuts, but individual differences in frequency and proficiency are marked Juveniles do most of the nut-cracking, but adults are, on average, more efficient; the frequency of inept stone manipulation decreases with age About 10% of the nut-cracking episodes were watched by other individuals—mostly infants and juveniles, suggesting a role for observational learning, even if restricted to stimulus enhancement

Orangutan Home Range Size and Its Determinants in a Sumatran Swamp Forest

Abstract: Orangutans (Pongo pygmaeus) in a Sumatran swamp forest used home ranges far larger than any described so far for the species, in spite of living at the highest density on record Although it was difficult to estimate home range sizes, minimum reliably estimated home range sizes for adult females are ca 850 ha, whereas subadult and adult males used ranges of at least ca 2500 ha, and perhaps much more Range overlap was very high: up to 16 adult females, 9 adult males and at least 15 subadult males were seen within a single 4-ha square in the center of the study area We found no evidence for the use of seasonally distincthome ranges—commuters—, and only some subadult males may have been transients—wanderers—without a stable home range The large size of the home ranges is attributed to the coarse grain of the habitat mosaic, with orangutans converging on parts with a high density of favored fruit trees Orangutans at this swamp forest included a variety of habitat types within their ranges

Neotropical Primates in a Regenerating Costa Rican Dry Forest: A Comparison of Howler and Capuchin Population Patterns

Abstract: Few data exist on how primate populations return to regenerating tropical forests. We compare the ways that two populations of neotropical monkeys, Alouatta palliata and Cebus capucinus, expanded over a 28-year period after the establishment of Santa Rosa National Park on reclaimed ranchlands in Costa Rica. We found that both howler and capuchin populations increased substantially in size subsequent to protection, but the howler population grew faster. This is likely due to their faster-paced life-history pattern than that of capuchins. The howler population increased mainly via the establishment of many new groups, whereas the capuchins expanded mainly by increasing the size of existing groups. We related this finding to the fact that capuchins are limited largely by their need to drink from water holes during the dry seasons whereas howlers are limited principally by their preference for largersized trees that occur in older forests. Proportions of adult male capuchins increased significantly during our study, likely due to skewed sex ratio at birth or male-biased immigration into the protected park or both factors. Our main finding is that, in as short a time period as 28 years, we can substantially enhance the size of monkey populations by allowing the regeneration of tropical forest. Furthermore, we provide a preliminary interpretation of how extrinsic factors—deforestation, hunting, crop-spraying, destruction of the watershed— and intrinsic variables, e.g., pace of reproduction; diet, differentially affect not only each species’ vulnerability to extinction but also its capacity to recover when human disturbances are minimized.

Fruit Availability and Habitat Use by Chimpanzees in the Kalinzu Forest, Uganda: Examination of Fallback Foods

Abstract: We studied seasonal change in habitat use by chimpanzees in the Kalinzu Forest, Uganda. The forest comprises various types of vegetation. For each vegetation type, we compared number of chimpanzees (per km2) that used the vegetation with fruit availability in different census periods. We estimated the number of chimpanzees by nest count and fruit availability via density of fallen fruit. The mixed mature forest contained a large amount of fruit during the high-fruiting season, but it decreased rapidly in the low-fruiting season. The number of chimpanzees also decreased in mixed mature forest in approximate proportion with fruit availability. In the Parinari-dominated mature and secondary forests, both fruit availability and number of chimpanzees were very low throughout the study. In the Musanga-dominated secondary forest, the number of chimpanzees increased toward the low-fruiting season, though the fruit availability decreased slightly. A multiple regression analysis showed that various fruits had significant effects on the number of chimpanzees during the high-fruiting season, while only Musanga leo-errerae had a significant effect during the low-fruiting season. The results suggest that the fruit of Musanga leo-errerae functions as a fallback food, and a combination of different vegetation types supports the chimpanzees in the Kalinzu Forest.

Territory Characteristics among Three Neighboring Chimpanzee Communities in the Taï National Park, Côte d'Ivoire

Abstract: We studied territory characteristics among three neighboring chimpanzee communities in the Tai National Park, Cote d'Ivoire, and compared them with other chimpanzee populations. We characterized territories and ranging patterns by analyzing six variables:, (1) territory size, (2) overlap zone, (3) territory utilization, (4) core area, (5) territory shift, and (6) travel distance. Data collection covered a period of 10 mo, during which we simultaneously sampled the local positions of mostly large parties, including males in each community, in 30-min intervals. In Tai, chimpanzees used territories in a clumped way, with small central core areas being used preferentially over large peripheral areas. Although overlap zones between study communities mainly represented infrequently visited peripheral areas, overlap zones with all neighboring communities also included intensively used central areas. Territory utilization was not strongly seasonal, with no major shift of activity center or shift of areas used over consecutive months. However, we observed shorter daily travel distances in times of low food availability. Territory sizes of Tai chimpanzees tended to be larger than territories in other chimpanzee communities, presumably because high food availability allows for economical defense of territorial borders and time investment in territorial activities. Therefore we suggest, that use of territory in Tai chimpanzees is strongly influenced by intercommunity relations. To understand differences in territory characteristics between various populations, it is of major importance to consider not only the intracommunity but also the intercommunity context.

Primate Nepotism: What is the Explanatory Value of Kin Selection?

Abstract: Kin selection theory (KS) is widely invoked to account for the preferential treatment of kin—nepotism—in primate societies. Because this idea is so pervasive the role of KS is often unquestioned and optional mechanisms are often ignored. I first examine the potential role of some other nepotism-generating mechanisms by concentrating on the effect of the proximity correlate of matrilineal kinship. This correlate of kinship may bias the development of mutually selfish interactions among relatives—kin-biased mutualism—and that of reciprocally altruistic interactions—kin-biased reciprocal altruism—two mechanisms that have been given little weight compared to KS and whose impact on the evolution of nepotism is therefore unknown. However, these two options to KS cannot account for the existence of unilaterally altruistic interactions among kin, which provide, therefore, the best type of evidence to test KS. But such evidence is difficult to obtain because many behaviors considered altruistic may in fact be selfish, and because kin altruism is seldom unilateral; it is most often bilateral, as expected by reciprocal altruism theory. For these reasons, one should be extremely cautious before equating nepotism exclusively with KS. Next, I examine the predictions of KS regarding the deployment of altruism according to degree of kinship by considering, in addition to the variables of Hamilton's equation, the duration of behaviors, the size of kin classes and their differential availability. In general, altruism is expected to be allocated at a fairly constant rate among kin categories and to drop markedly past the degree of relatedness beyond which altruism is no more profitable. Very little data allow one to test conclusively this prediction, as well as some other significant predictions. Overall, there is ample evidence for the role of KS in shaping mother-offspring interactions in various areas. But the evidence for kin-selected altruism beyond the mother-offspring bond (r < 0.5), though qualitatively solid, is much less abundant. Kin altruism drops markedly beyond r = 0.25 (half-siblings and grandmother-grandoffspring dyads).

Activity and Ranging Patterns of Guerezas in the Kakamega Forest: Intergroup Variation and Implications for Intragroup Feeding Competition

Abstract: From March 1997 to February 1998, I investigated the activity patterns of 2 groups and the ranging patterns of 5 groups of eastern black-and-white colobus (Colobus guereza), aka guerezas, in the Kakamega Forest, Kenya. Guerezas at Kakamega spent more of their time resting than any other population of colobine monkeys studied to date. In addition, I recorded not one instance of intragroup aggression in 16,710 activity scan samples, providing preliminary evidence that intragroup contest competition may be rare or absent among guerezas at Kakamega. Mean daily path lengths ranged from 450 to 734 m, and home range area ranged from 12 to 20 ha, though home range area may have been underestimated for several of the study groups. Home range overlap was extensive with 49–83% of each group's range overlapped by the ranges of other groups. Despite the high level of home range overlap, the frequently entered areas (quadrats entered on ≥30% of a group's total study days) of any one group were not frequently entered by any other study group. Mean daily path length is not significantly correlated with levels of availability or consumption of any plant part item. Mean daily path length is also not significantly correlated with group size, though the largest group did have the longest mean daily path length. This finding suggests that intragroup scramble competition may have been rare or absent among guerezas at Kakamega except perhaps in the largest group, which was unusually large.

Nutritional Aspects of Western Lowland Gorilla (Gorilla gorilla gorilla) Diet During Seasons of Fruit Scarcity at Bai Hokou, Central African Republic

Abstract: Traditionally, gorillas were classified as folivores, yet 15 years of data on western lowland gorillas (Gorilla gorilla gorilla) show their diet to contain large quantities of foliage and fruit, and to vary both seasonally and annually. The consumption of fruit by gorillas at Bai Hokou, Central African Republic, is correlated with rainfall and ripe fruit availability (Remis, 1997a). We investigated the nutritional and chemical content of gorilla foods consumed at Bai Hokou during two seasons of fruit scarcity as measured by phenological observations and compared our findings with the nutrient content of gorilla foods at other African sites. We conclude that during lean times, Bai Hokou gorillas consumed fruits with higher levels of fiber and secondary compounds than those of other populations of western lowland or mountain gorillas. Conversely, leaves consumed by Bai Hokou gorillas were relatively low in fiber and tannins. Bai Hokou gorillas appeared to meet their nutritional needs by eating a combination of fruit and foliage. They ate fruits comparatively high in secondary compounds and fiber when necessary. While gorillas are selective feeders, wherever and whenever preferred foods are scarce, their large body size and digestive anatomy enable them to consume and process a broader repertoire of foods than smaller bodied-apes.

Park or Ride? Evolution of Infant Carrying in Primates

Abstract: Few mammalian orders carry their infants clinging to the mother's fur. I investigated the evolution of carrying behavior in primates and the life-history and ecological correlates of infant care patterns. Primates are ideal for the study as there is variation in infant care patterns. Primate infants are left hidden in nests or parked in trees, both of which strategies I term parking, and are carried orally or ride clinging to the mother's fur: riding. Infant carrying has evolved several times in the Primates and, once evolved, it has been conserved. Significant energetic costs of riding are indicated as riding species maintain smaller home ranges than those of non-riders of the same body size. With body size and phylogenetic influences taken into account, riders appear to incur a reproductive cost by weaning and breeding later than parkers. Although riders do not have lower birth rates than those of parkers, their later age at first reproduction leads to their having a lower reproductive rate, measured by the intrinsic rate of population increase. Precociality of infants is not correlated with either riding or nesting behavior. Although non-nesting species have larger litter sizes, their infants are not significantly smaller, nor are their neonatal brains relatively smaller. Although riding may have some energetic and reproductive costs, its repeated evolution in the Primates suggests that it also has some benefits, the most likely being a reduced mortality risk for carried infants.

Primate Population Densities and Sizes in Atlantic Forest Remnants of Northern Espírito Santo, Brazil

Abstract: We surveyed primates in seven fragments of Atlantic forest ranging from 210 to 24,250 ha in Espirito Santo, southeastern Brazil. The objective was to assess their population densities and fragment-specific population sizes in order to discuss the survival of primates in this highly fragmented landscape. We used line-transect sampling for censusing primates and estimated densities via DISTANCE program. Alouatta fusca, Cebus apella, Callicebus personatus, and Callithrix geoffroyi live in the study area. Although variable, primate numbers were higher in larger than in smaller fragments, the likely reasons being the lack of space and food resources (fruits) and higher impact of mesopredators (small cats) in small fragments. The estimated densities are within the range reported for other Atlantic forest sites, except for brown howlers (Alouatta fusca), which were extremely rare. Estimates of population sizes were on the order of several hundreds to thousands of individuals/species in the large-sized fragments (ca. 20,000 ha), while comparable estimates for the other areas indicate <500 individuals/species in the medium-sized reserves (ca. 2,000 ha), and <50 individuals/species in the small fragments (ca. 200 ha). These estimates suggest that only Atlantic forest fragments ≥20,000 ha can harbor primate populations large enough to escape extinction in the long term. Given that <20% of all protected areas remaining in the Atlantic forest are ≥20,000 ha, management measures are urgently needed to improve primate conservation in this biome.

Food Resource Characteristics in Two Nocturnal Lemurs with Different Social Behavior: Avahi occidentalis and Lepilemur edwardsi

Abstract: I present results from a comparative field study on the feeding behavior of the gregarious Avahi occidentalis and the solitary-but-social Lepilemur edwardsi to evaluate hypotheses relating to social organization and food resources. While Avahi and Lepilemur are both nocturnal, have comparable body weights and positional behaviors, and are both folivorous, they differ in their social organization. Therefore, they present an ideal model for assessing food resource characteristics through comparisons of food selection in both species with regard to forest composition. The monogamous Avahi tend to select under-represented resources. They are repeatedly exploited, which suggests that their location must be known. It is worthwhile and probably imperative to defend those resources. Such defense imposes ranging limitations on male Avahi. Females may prefer familiar mates that will share their knowledge of resource location and defend the resources. A stable monogamous pattern could be the optimal strategy. In contrast, food selection by Lepilemur is based on common resources to a higher degree, but they show a lower degree of exploitation. Lepilemur males would be less restricted and could potentially opt for a different strategy, e.g., a dispersed harem. It is unclear whether this strategy is realized or not. I discuss other possible correlates of monogamy—infanticide protection, predation avoidance—but the gregarious pattern in Avahi may best be seen as a retention, and its nocturnal activity as a secondary adaptation.

Time Allocation Patterns of Lowland Woolly Monkeys (Lagothrix lagotricha poeppigii) in a Neotropical Terra Firma Forest

Abstract: We investigated the time allocation decisions of lowland woolly monkeys (Lagothrix lagotricha poeppigii )i n aterra firma forest in eastern Ecuador where they occur sympatrically with 9 other primate species. Woolly monkeys spent considerable amounts of time searching for and attempting to procure animal prey—roughly as much time as they spent consuming plant material: ripe fruits, leaves, and flowers. The amount of time spent foraging for animal prey is positively related to the habitat-wide availability of ripe fruits (the predominant component of the woolly monkey diet), and negatively related to both ambient temperature and the abundance of potential prey items in the habitat. Time spent resting showed exactly the opposite pattern with respect to these ecological variables. These results suggest that woolly monkeys follow an energy-maximizing strategy of food acquisition during times of fruit abundance—focusing on animal foods and perhaps laying down fat reserves to utilize when ecological conditions worsen—and follow an energy-minimizing strategy when fruit resources are scarce. Such a strong and seasonal commitment to animal prey foraging is unique among the ateline primates and is not ubiquitous even among lowland woolly monkeys. We suggest that this foraging strategy, and the greater intragroup cohesion that characterizes some populations of Lagothrix, are both opportunistic responses to regional differences in habitat quality. Identifying and accounting

Dietary Differences Among Sympatric Callitrichinae in Northern Bolivia: Callimico goeldii, Saguinus fuscicollis and S. labiatus

Abstract: Studies of sympatric species can provide important data to define how dietary and habitat requirements differ among them. I collected dietary data during a first yearlong comparative study of wild groups of Callimico goeldii, Saguinus labiatus and S. fuscicollis. Dietary overlap was highest between Saguinus fuscicollis and Saguinus labiatus throughout the year, and lowest between Saguinus labiatus and Callimico goeldii. All three species had high dietary overlap in February and March when a few abundant fruit species dominated their diets. Although all three species rely heavily on many of the same fruits and arthropods, there are several important distinctions among their diets. Surprisingly, Callimico goeldii consume large quantities of fungus throughout the year: 29% of annual feeding records. Mycophagy is more frequent in the dry season when fruits are scarce. In contrast, Saguinus labiatus rarely eat fungus during the period of fruit scarcity, and instead rely on nectar, a resource never exploited by Callimico goeldii. Saguinus fuscicollis also rely on nectar during periods of low fruit availability and increase their intake of arthropods and exudates. During April, a period of fruit scarcity, exudates comprise >50% of the feeding records of Saguinus fuscicollis. The use of different food resources during fruit scarcity, and differences in the heights at which each species feeds and forages appear to define a distinct ecological niche for each of them and allow them to maintain long-term associations throughout the year. Furthermore, I hypothesize that the limited distribution of Callimico goeldii may result from their restriction to forests that have high disturbance rates, where microhabitats appropriate for fungal growth are abundant, but which also contain abundant fruit and insects.

What Factors Affect the Size of Chimpanzee Parties in the Kalinzu Forest, Uganda? Examination of Fruit Abundance and Number of Estrous Females

Abstract: We examined factors affecting the size of chimpanzee parties in the Kalinzu Forest, Uganda. We found that the number of individuals in a party increased with observation time. Therefore, we employed two methods to reduce this bias: (1) we evaluated party size via the mean number of individuals observed in each 1-h period during the observation of a party (1-h party size), and (2) we used the number of all individuals observed in a party (1-day party size) and performed an analysis of covariance, with observation time of the party as the covariant. We examined factors that might affect party size: fruit abundance, fruit distribution, and number of estrous females. There was no relationship between party size and fruit abundance or distribution. Conversely, the number of males has a significant positive correlation with the number of estrous females, though there is no correlation with the number of anestrous females. These results suggest that males tended to join parties with more females in estrous, irrespective of differences in fruit availability.

Self-induced Increase of Gut Motility and the Control of Parasitic Infections in Wild Chimpanzees

Abstract: When physiological adaptation is insufficient, hosts have developed behavioral responses to avoid or limit contact with parasites. One such behavior, leaf-swallowing, occurs widely among the African great apes. This behavior involves the slow and deliberate swallowing without chewing of whole bristly leaves. Folded one at a time between tongue and palate, the leaves pass through the gastro-intestinal (GI) tract visibly unchanged. Independent studies in two populations of chimpanzees (Pan troglodytes schweinfurthii) showed significant correlations between the swallowing of whole leaves and the expulsion of the nodule worm Oesophagostomum stephanostomum and a species of tapeworm (Bertiella studeri). We integrate behavioral, parasitological and physiological observations pertaining to leaf-swallowing to elucidate the behavioral mechanism responsible for the expulsion and control of nodule worm infections by the ape host. Physical irritation produced by bristly leaves swallowed on an empty stomach, increases motility and secretion resulting in diarrhea which rapidly moves leaves through the GI tract. In the proximal hindgut, the site of third-stage larvae (L3) cyst formation and adult worm attachment, motility, secretion and the scouring effect of rough leaves is enhanced by haustral contractions and peristalsis-antiperistalsis. Frequently, at the peak of reinfection, a proportion of nonencysted L3 is also predictably vulnerable. These factors should result in the disruption of the life cycle of Oesophagostomum spp. Repeated flushing during peak periods of reinfection is probably responsible for long-run reduction of worm burdens at certain times of the year. Accordingly, leaf-swallowing can be viewed as a deliberate adaptive behavioral strategy with physiological consequences for the host. The expulsion of worms based on the activation of basic physiological responses in the host is a novel hitherto undescribed form of parasitic control.

Feeding Ecology of Guerezas in the Kakamega Forest, Kenya: The Importance of Moraceae Fruit in Their Diet

Abstract: Eastern black-and-white colobus (Colobus guereza), or guerezas, have long been considered to be one of the most folivorous primates. I conducted a study of the feeding ecology of two guereza groups (T and O) over an annual cycle in the Kakamega Forest of western Kenya. I found that the annual diets of both groups comprised mostly of leaves (T: 48%, O: 57%) though fruit (T: 44%, O: 33%) also accounted for a substantial portion of the diet. In the six months when fruit was most abundant, fruit consumption constituted an average of 58% of T-group's monthly diet and 42% of O-group's monthly diet. In contrast to most previous studies of colobines, in which seeds were the primary fruit item consumed, almost all of the fruit eaten by guerezas at Kakamega consisted of whole fruits. At least 72% of the whole fruits consumed by T-and O-groups were whole fruits from trees in the Moraceae family, which dominates the tree family biomass at Kakamega. Unlike at sites where guerezas consumed fruit primarily when young leaves were scarce, at Kakamega guerezas ate fruit in accordance with its availability and irrespective of the availability of young leaves. My findings demonstrate that guerezas are more dietarily flexible than was previously known, which may help to explain why the species can survive in such a wide variety of forested habitats across equatorial Africa.

Developmental aspects of sexual dimorphism in hominoid canines

Abstract: We examined the histology of canine teeth in extant hominoids and provided a comparative database on several aspects of canine development. The resultant data augment the known pattern of differences in aspects of tooth crown formation among great apes and more importantly, enable us to determine the underlying developmental mechanisms responsible for canine dimorphism in them. We sectioned and analyzed a large sample (n = 108) of reliably-sexed great ape mandibular canines according to standard histological techniques. Using information from long- and short-period incremental markings in teeth, we recorded measurements of daily secretion rates, periodicity and linear enamel thickness for specimens of Pan troglodytes, Gorilla gorilla, Pongo pygmaeus and Homo sapiens. Modal values of periodicities in males and females, respectively, are: Pan 7/7; Gorilla 9/10; Pongo 10/10; and Homo 8/8. Secretion rates increase from the inner to the outer region of the enamel cap and decrease from the cuspal towards the cervical margin of the canine crown in all great ape species. Female hominoids tend to possess significantly thicker enamel than their male counterparts, which is almost certainly related to the presence of faster daily secretion rates near the enamel-dentine junction, especially in Gorilla and Pongo. Taken together, these results indicate that sexual differences in canine development are most apparent in the earlier stages of canine crown formation, while interspecific differences are most apparent in the outer crown region. When combined with results on the rate and duration of canine crown formation, the results provide essential background work for larger projects aimed at understanding the developmental basis of canine dimorphism in extant and extinct large-bodied hominoids and eventually in early hominins.

Reproductive Socioecology of Tufted Capuchins (Cebus apella nigritus) in Northeastern Argentina

Abstract: We describe the reproductive parameters of tufted capuchins (Cebus apella nigritus) in the Iguazu National Park, NE Argentina. We obtained data on six different groups (33 individually recognized adult females) studied for periods of 2–9 years. Estimated birthrate is 0.59 infants per female per year in unprovisioned groups. A group that was provisioned for 6 years during the winter period of low fruit availability (May–August), showed a similar birth rate of 0.61, but a lower infant mortality rate than unprovisioned groups. The birthrate estimated for this population is higher than the one reported for white-faced and wedge-capped capuchins. The mean interbirth interval is 19.35 months, but a female can have infants in successive years, even when her previous infant has survived. The modal age at first delivery is 7 years, which is similar to the one observed in wedge-capped capuchins. When young adult females come into estrous they avoid copulating with the alpha male that sired them, thus providing evidence for a behavioral mechanism of inbreeding avoidance. Births are very seasonal at Iguazu, occurring during the spring and summer months (October–February) when food availability is at its peak. Tufted capuchins at Iguazu are more seasonal breeders than other capuchin populations, probably as a result of their more seasonal environment. The secondary sex ratio does not deviate significantly from 1:1, despite the known ability of capuchins to adjust secondary sex ratio to local conditions.

Regulation by photoperiod of seasonal changes in body mass and reproductive function in gray mouse lemurs (Microcebus murinus) : Differential responses by sex

Abstract: Microcebus murinus exhibits highly seasonal biological rhythms to cope with extreme seasonality in availability of resources. To study the role of daylength on seasonal changes in body mass and reproductive function, we exposed male and female gray mouse lemurs to natural, constant, or alternating light cycles for 2 years under constant environmental conditions. When exposed to either constant short (SD: 10 h light/day), long (LD: 14 h light/day), or intermediate (ID: 12 h light/day) daylength, males and females maintained a constant body mass with no spontaneous cyclic variation. We only observed typical seasonal body mass changes in subjects exposed to alternating periods of SD and LD, the weight gain being triggered by SD, whereas weight loss occurred under LD. Reproductive activity in females proceeded from an endogenous rhythm that was expressed under constant daylengths. In contrast, changes in reproductive activity in males depended on daylength variation. In both sexes, SD and LD have direct inhibitory or stimulatory effects on reproductive activity. In females, daylength regulates breeding season by synchronizing an endogenous sexual rhythm with the season, whereas in males, the perception of a critical photoperiod is used to determine the subsequent onset or arrest of their breeding season. These sexual differences in the effect of daylength could be related to sex-specific differences in reproductive constraints.

Feeding, diet, and jaw form in West African Colobus and Procolobus

Abstract: 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

Ranging Behavior of Two Species of Guenons (Cercopithecus lhoesti and C. mitis doggetti ) in the Nyungwe Forest Reserve, Rwanda

Abstract: I studied the ranging behavior of one group of L'Hoest's monkeys (Cercopithecus lhoesti) and one group of blue monkeys (C. mitis doggetti) in the Nyungwe Forest Reserve, Rwanda. This study is the first to examine the ranging behavior of the more terrestrial L'Hoest's monkeys. Fruits composed 47% of blue monkey diet and 24% of the L'Hoest's monkey diet; terrestrial herbaceous vegetation composed 35% of the diet of the latter. While overall abundance of fruit resources in the home range and overall proportion of fruit in the diet were not related to ranging behavior in either group, temporal and spatial availability of specific fruit species was related. Measures of ranging behavior indicated a more concentrated ranging pattern when fruit resources were scarce and dietary diversity increased and when fruit resources were abundant and the groups focused on a few abundant fruit species. Current hypotheses concerning primate ranging behavior suggest that frugivorous species are expected to have greater day ranges and larger home ranges than folivorous species, and invertebrate consumption is expected to produce a more wide-ranging pattern. However, the L'Hoest's monkey group, which was more folivorous and consumed fewer invertebrates, traveled greater daily distances, had a more diverse and longer ranging pattern, and had larger home range areas than the blue monkey group in every month of the study. Both species were highly selective of forest habitats; L'Hoest's monkeys used secondary forest, while blue monkeys preferred primary forest.

Red-tailed guenons (Cercopithecus ascanius) and Strychnos mitis: Evidence for plant benefits beyond seed dispersal

Abstract: I report data collected on red-tailed guenon (Cercopithecus ascanius schmidti) fruit processing behaviors between June 1993 and April 1994. Red-tailed guenons consumed the fruit of Strychnos mitis in 542 of 2,930 fruit-eating events (FEEs). The monkeys spat out cleaned seeds of Strychnos mitis in a majority of these records (477/542; 88%); seeds were occasionally swallowed whole, but only when pulp was unripe (69/542; 12%). In 83% of the FEEs on Strychnos, the red-tailed guenons spat out seeds within 10 m of the removal site; they typically stayed in the same tree while processing fruit, and in 56% of the FEEs, they moved <1 m before spitting seeds. I monitored spat seeds to evaluate the impact of monkey fruit processing on seed fate. Results indicate that 83% of seeds spat out by the red-tailed guenons germinated, while only 12% of unprocessed seeds survived to germination (p < 0.01). Of the processed seeds that germinated, 60% survived to germination and seedling establishment, while only 5% of unprocessed seeds survived to seedling establishment (p < 0.01). Unprocessed seeds were also more likely to be attacked by seed predators (p < 0.01) and fungus (p < 0.01). Although there is generally high mortality in seeds/seedlings, mature trees of Strychnos mitis are found in groves of adults, under which dense populations of seedlings and saplings can occur. These data suggest that Strychnos mitis does not conform to expectations of the Janzen-Connell model of seed escape from parent trees. Instead, I suggest that by removing pulp, a process that results in a reduction of fungal pathogen attack, red-tailed guenons positively effect the seed survivorship of Strychnos mitis. Although this effect has been observed in pulp-cleaning ant species, it is a hitherto undescribed effect of primates on their fruit resources.

Distribution and Habitat Associations of Baboons (Papio hamadryas) in Central Eritrea

Abstract: At least three diurnal primate taxa are still present in Eritrea, NE Africa: hamadryas baboons (Papio hamadryas hamadryas), olive baboons (Papio h. anubis) and grivet monkeys (Chlorocebus aethiops aethiops). However, information on status and distribution of primates and their habitats in Eritrea is outdated and incomplete. We conducted a primate survey, focussing on hamadryas baboons, to obtain data which will be integrated in a national wildlife management and conservation plan in Eritrea. We obtained information about the geographical distribution and abundance of baboons, their altitudinal range, habitat quality of their home-ranges, aggregation sizes at sleeping cliffs and predator presence. We described habitat quality via the Normalized Difference Vegetation Index (NDVI), a vegetation classification of Landsat MSS satellite data. Hamadryas and olive baboons are still present in Eritrea in ample numbers. Their geographical distributions in 1997 and 1998 did not deviate significantly from their historical distributions. An estimated 15,000 Papio hamadryas hamadryas lived in the 25,000-km2 area of survey (0.58 baboons/km2). Population densities of hamadryas baboons in many parts of the survey area are higher than at Kummer's (1968) study site in Ethiopia. Hamadryas baboons live at all altitudes in four of five ecogeographical zones of Eritrea. Olive baboons replaced them in the western lowlands. Both baboon taxa tend to select better quality habitats, characterized by a higher normalized difference vegetation index (NDVI) than the average for the respective ecogeographical zones. Hamadryas baboons show a greater ecological plasticity than olive baboons, which are confined to riverbeds with extended gallery forest. By the end of 1999, a hybrid zone could not be confirmed.

Extended Application of a Marked-Nest Census Method to Examine Seasonal Changes in Habitat Use by Chimpanzees

Abstract: The Kalinzu Forest Reserve in Uganda comprises various types of vegetation, including mixed mature forest, Parinari-dominated mature and secondary forest, and Musanga-dominated secondary forest. We used a marked-nest census method to examine seasonal changes in chimpanzees' use of the different vegetation types. We made 10 parallel line-transects in the study area; they were 5-km long and 500-m apart. During the first 3–4 walks along the transects, we marked all existing nests. We then conducted 10 main censuses of all transects at 15-day intervals, over a total period of about 5 months. In each main census, we recorded all unmarked nests visible from the transects and marked them. When we saw a nest, we searched for neighboring nests of the same age class ≤30 m of each other, in order to estimate the size and position of nest groups. To improve the accuracy of the estimation of nest density in each census period, we excluded nests that consisted only of brown leaves and corrected the number of nests observed by allowing for the proportion of newly-built nests that would still have green leaves at the next main census. We estimated the population density of chimpanzees in the study area both by the number of individual nests and by the number of nest groups; the two methods gave similar results. We found differences in number of chimpanzees that used different vegetation types in different fruiting seasons, and differences in nest group size related to the different fruiting seasons.

Shifts in Social Structure of Black Howler (Alouatta pigra) Groups Associated with Natural and Experimental Variation in Population Density

Abstract: We examined variation in the group structure of black howlers (Alouatta pigra) using the adult composition of 48 social groups. We compared the structure of groups at 5 sites with different population densities and variation in group structure over time with rising population density. In addition, we examined changes in the group structure of monkeys that were translocated from an area of high population density to an area with a much lower population density. We found at low population densities, groups comprised either heterosexual pairs or a single male with two females. At high population densities groups tended to be multimale and often contained >2 adult females. We suggest the relative costs and benefits of dispersal by maturing adults varies with population density, and in Alouatta pigra results in a shift from single to multimale groups of larger size with increasing population density.

Daily Torpor in Free-Ranging Gray Mouse Lemurs (Microcebus murinus) in Madagascar

Abstract: I aimed to determine when and under which seasonal environmental conditions gray mouse lemurs (Microcebus murinus), a small nocturnal primate species endemic to Madagascar, utilize daily torpor. Using temperature-sensitive radio collars, I measured skin temperature (T sk ) of free-ranging mouse lemurs under natural conditions. My results showed that male and female mouse lemurs in the wild enter torpor spontaneously over a wide range of ambient temperatures (T a ) during the dry season, but not during the rainy season. Mouse lemurs that remained normothermic had significantly lower body masses (mean: 59.7 g) than individuals that used torpor (mean: 80.2 g). Skin temperatures dropped to 20.9°C and the mean torpor bout duration is 10.3 h. The use of torpor on a given night varied among individuals, whereas the propensity for torpor did not differ significantly between males and females. I found no evidence that T a can be used to predict whether mouse lemurs will remain normothermic or enter torpor. It appears that the most reliable indicator for the occurrence of torpor in free-ranging Microcebus murinus is time of the year, i.e., photoperiod.

Comparison of Reproductive Characteristics and Changes in Body Weight Between Captive Populations of Rufous and Gray Mouse Lemurs

Abstract: The nocturnal Malagasy mouse lemurs are among the smallest primates worldwide. Several sibling species are known. Of these, the rufous and the gray mouse lemur differ with respect to morphology, genetics, and communication. They might also differ in seasonal reproduction and body weight changes. We investigated and compared reproductive activities and changes in monthly body weight in males and females of successfully breeding colonies of both species under the same photoperiodic conditions. Females of both species showed estrous cycles only during the long-day period. Rufous mouse lemur females seemed to have a shorter gestation than their sibling species (57 vs. 62 days). The number of estrous cycles (2.25 vs. 2.5/season) and their lengths (59 vs. 52 days) were similar. Litter size (2) seemed to be similar. Latency of estrous occurrence after photoperiodic stimulation was longer in Microcebus rufus than in its sibling species (71.6 and 42.3 days). The same was true for the onset of the growth of the testes. The rate of growth and size of the testes were similar, and precede the estrous onset in both species. The reproductive activity was shorter in both sexes of the rufous than of the gray mouse lemurs. In both species, body weight showed similar seasonal changes. Males lost more weight during the breeding season than females did. In rufous mouse lemurs, body weight was similar in both sexes during the nonbreeding season. In gray mouse lemurs, sexes differed throughout the year.

Behavioral and Hormonal Analysis of Social Relationships Between Oldest Females in a Wild Monogamous Group of Common Marmosets (Callithrix jacchus)

Abstract: Social organization in common marmosets (Callithrix jacchus) appears to be based on a hierarchy of dominance, in which dominant females limit the reproductive functioning of subordinates. Reduced fertility was documented for captive but not for wild females. We investigated social dynamics and hormonal profiles of females living in a wild group. We collected behavioral and hormonal data during 7 mo from the reproductive and two nonreproductive adult females (probably daughters), and their interactions with the reproductive male. The subjects lived in a monogamous group at Nisia Floresta field station in northeastern Brazil. We collected behavioral data as all day follows, once a week and fecal material twice a week. We analyzed fecal samples for cortisol and progesterone using enzyme immuno assay (EIA) techniques. During the first three months we monitored the reproductive female (GRE) and the oldest nonreproductive female, (GIO). After the disappearence of GIO, we monitored the next oldest subordinate adult female, (GRA). GRE had just given birth at the beginning of the study, and she gave birth 6 mo later. During the last 2 weeks of GRE's gestation, GRA showed elevated progesterone levels, indicating ovarian cycling. Cortisol levels from GRE and GRA reached very high levels then. During GRA's cycling period, her interactions with the reproductive male (GT) were lower than when she was not cycling. We saw sexual interactions only between GT and GRE. The results provide evidence that ovarian function in mature subordinate females might be affected by the reproductive condition of the dominant female.

Food habits of Formosan rock macaques (Macaca cyclopis) in Jentse, Northeastern Taiwan, assessed by fecal analysis and behavioral observation

Abstract: We studied the food habits of the Formosan rock macaques (Macaca cyclopis) in Jentse via fecal analysis and direct field observation from October 1991 to September 1992, and recorded macaques eating 51 plant species and insects of ≥5 orders. Macaques in Jentse spent more time feeding on fruits than on other plant parts or insects. However, there was seasonal variation in their food habits, i.e., they spent a higher proportion of time feeding on fruits and insects in summer, and on leaves and stems in winter. The major plant species consumed and the patterns of seasonal variation in the macaque diets identified by fecal analysis and field observation are similar. However, there are discrepancies between results from the two methods in some of the finer details of estimated dietary composition.