Predicting the Competitive Regime of Female <Emphasis Type="Italic">Colobus vellerosus</Emphasis> from the Distribution of Food Resources

We examined the spatial and temporal distribution of the foods of ursine colobus (Colobus vellerosus) at Boabeng-Fiema, Ghana as a means to predict the monopolizablity and usurpability of their food resources. Recent evidence suggests that food may not be limiting for folivorous primates, and that male sexual coercion may be a more important influence on folivore social organization. To address the question, we collected focal data on the feeding behavior of adult females and males over 11 mo (September 2000-August 2001) on 2 groups: WW (n = 31–33 individuals) and B (n = 8–16 individuals). We also conducted phenological monitoring and a tree survey of the two-group home ranges to establish food availability and distribution. We used 2 behavioral or organism-defined indicators of feeding behavior to assess potential resource contestability: food site residence time and distance moved between food sites. The colobus fed on a high diversity of species, most of their food trees were not clumped in distribution, within-tree interfood distances were short, and food trees were large. The only condition associated with the potential for monopolization was low food tree density. However, low food tree density may be offset by the colobus’ use of large trees. Taken together, the ecological and behavioral indicators suggest the food resources of Colobus vellerosus had a low potential for monopolization. Our results also indicate mature leaves had the longest food site residence time, which may suggest they should be the most usurpable plant part, though their presumed low quality and high abundance probably counteracted the effect. The pattern implied the potential for direct feeding competition among Colobus vellerosus at Boabeng-Fiema was low and agonistic interactions over food are not expected. Instead, a group size effect on feeding efficiency should be a more predominant influence on feeding efficiency, if food is limiting for the species.     

Effect of Group Size on Activity Budgets of Colobus vellerosus in Ghana

Group size influences foraging efficiency in several primates. We examined the activity budgets of 3 groups of Geoffroy's pied colobus (Colobus vellerosus) at the Boabeng-Fiema Monkey Sanctuary in Ghana to determine whether larger group size induces scramble competition. We studied 2 groups (B1; N = 7-8 and WW; N = 31-33) occupying slightly overlapping home ranges from August to November 2000. We observed the third group, B2 (N = 15-16), comprising B1 and 7 male invaders in the same home range as B1 from August to November 2001. By comparing groups belonging to the same population and occupying sligthly overlapping or similar home ranges, we were able to control, to a certain extent, for differences in food distribution. We recorded a total of 3353 scans, yielding 14,886 activity records, over 73 days. As with other black-and-white colobus, resting was their most common activity (59%). Intergroup comparisons suggest that time spent feeding, resting and moving did not vary in relation to group size. However, intragroup comparisons between the sexes show that females in the large group spent more time feeding than males did, whereas this was not the case in the small group, which suggests that scramble competition may be occurring among female Colobus vellerosus at BFMS. It is also possible that this may be due to greater nutritional requirements because of a higher proportion of infants in the large group. In fact, the proportion is quite similar between the two groups, lending support to the idea that females in the two groups had comparable nutritional demands due to lactation. This suggests that increased feeding in females in the large group was partly an effect of scramble competition. Group size and group composition also influenced the frequency of social behavior. There was more grooming in the large group, and it was performed mostly by females. The distribution of activities throughout the day was similar to the pattern reported for other black-and-white colobus.     

Test of the ecological-constraints model on ursine colobus monkeys (Colobus vellerosus) in Ghana

For group-living mammals, the ecological-constraints model predicts that within-group feeding competition will increase as group size increases, necessitating more daily travel to find food and thereby constraining group size. It provides a useful tool for detecting scramble competition any time it is difficult to determine whether or not food is limiting. We tested the ecological-constraints model on highly folivorous ursine colobus monkeys (Colobus vellerosus) at the Boabeng-Fiema Monkey Sanctuary in Ghana. Three differently sized groups were followed for 13 months and two others were followed for 6 months each in 2004-2005 using focal-animal sampling and ranging scans; ecological plots and phenology surveys were used to determine home-range quality and food availability. There was relatively little difference in home-range quality, monthly food availability, diet, adult female ingestion rates, and rate of travel within food patches between the groups. However, home-range size, day-range length, and percent of time spent feeding all increased with group size. We performed a single large test of the ecological-constraints model by combining several separate Spearman correlations, each testing different predictions under the model, using Fisher's log-likelihood method. It showed that the ecological-constraints model was supported in this study; scramble competition in this population is manifesting in increased ranging and time spent feeding. How costly this increased energy expenditure is for individuals in larger groups remains to be determined.     

Feeding Competition and Agonistic Relationships Among Bwindi <Emphasis Type="Italic">Gorilla beringei</Emphasis>

Testing predictions of socioecological models, specifically that the types of feeding competition and social relationships female primates exhibit are strongly influenced by the distribution, density, and quality of food resources, requires studies of closely related populations of subjects living under different ecological conditions. I examined feeding competition and the resulting female social relationships in mountain gorillas (Gorilla beringei beringei) of Bwindi Impenetrable National Park, Uganda, which has ecological conditions distinctive from those where other gorilla populations live. I observed 1 group of gorillas for 29 mo to examine the proportion of time spent foraging on fruit, the relationship between patch size and occupancy patterns of fruit trees, and agonistic interactions. Patch occupancy time while foraging in fruit trees decreased with increasing number of gorillas in a tree and decreasing tree size, suggesting that fruit trees represent limiting patches and can lead to intragroup scramble competition. Gorillas exhibited higher levels of aggression while feeding on fruit versus other food resources, which indicates intragroup contest competition. I observed a linear dominance hierarchy with no bidirectionality via displacements, and a similar hierarchy via aggression, though a notable proportion of the dyads contained 2-way interactions. However, most aggression was of low intensity (vocalizations) and the recipient typically ignored it. Despite differences in ecological conditions and diet between the Virunga Volcanoes and Bwindi, agonistic relationships among females are largely similar in the 2 populations and are best characterized as dispersal individualistic.     

Activity and Ranging Patterns of <Emphasis Type="Italic">Colobus angolensis ruwenzorii</Emphasis> in Nyungwe Forest,Rwanda: Possible Costs of Large Group Size

With group sizes sometimes >300 individuals, the Angolan black-and-white colobus (Colobus angolensis ruwenzorii) population in Nyungwe Forest, Rwanda is an intriguing exception to the tendency for folivores to live in smaller groups than expected relative to body size. Researchers have hypothesized that the unusually high quality of foliage at Nyungwe allows colobus there to avoid intragroup feeding competition, releasing constraints on the formation of large groups (Fimbel et al., 2001). We collected data on the activity and ranging patterns of a >300-member Nyungwe colobus group and compared our results to those from smaller groups in other black-and-white colobus (Colobus spp.) populations. Colobus at Nyungwe spent far more time feeding and moving (62%) and far less time resting (32%) than black-and-white colobus at any other site. The annual home range of the Nyungwe colobus was also many times larger (95% minimum convex polygon: 20.7 km ² ; 95% fixed kernel: 24.4 km ² ) than those for other populations. We terminated our research after the group engaged in an unprecedented migration among black-and-white colobus by moving 13 km south of their former range. Our results suggest that intragroup scramble competition may be more intense than originally believed within the large colobus groups at Nyungwe and that long periods of resource renewal may be necessary after a large colobus group passes through an area, thereby potentially helping to explain their wide ranging patterns. We discuss the socioecological convergence between the Nyungwe colobus and Chinese snub-nosed monkeys (Rhinopithecus spp.) and suggest directions for future research on the unique black-and-white colobus population at Nyungwe.

Food Competition Between Wild Orangutans in Large Fig Trees

Orangutans are usually solitary. However, occasionally aggregations are formed, especially in large fruiting fig trees. Individuals in these aggregations may experience scramble or contest competition for food. We investigated the type and strength of food competition in large figs among wild Sumatran orangutans. Adult males foraged more efficiently than adult females and subadult males did. The availability of ripe fruit is positively related to the number of orangutans visiting a fig tree and their foraging efficiency. The number of orangutans in a fig tree did not affect patch residence time and foraging behavior, though orangutans spent more time feeding when aggregation size increased in a fig tree. Dominance relationships could be measured in a number of dyads. Differences in dominance did not affect foraging behavior. The patch residence time of subordinate individuals was reduced on days that a dominant individual also visited the fig. In conclusion, orangutans seem to adjust aggregation size to the number of available ripe fruits in a fig tree in such a way that scramble competition was absent. Contest competition determined access to large fig trees.     

Feeding Ecology of <Emphasis Type="Italic">Trachypithecus pileatus</Emphasis> in India

We observed a group of capped langurs for 12 mo in the Pakhui Wildlife Sanctuary, Arunachal Pradesh, India. We recorded the time of feeding on different food plant species, food categories, and the feeding heights of monkeys in trees. Capped langurs spent 68% of their feeding time on leaves, 16% on flowers, and 16% on fruits. Feeding on leaves was consistently high (p < 0.01) during the year, with the highest feeding in May (85%) and the lowest in January (47%). The seasonal difference in feeding on leaves is significant (p < 0.05): it was higher in summer and during monsoon. The feeding time on flowers was maximal (35%) in March and that on fruits and seeds was minimal (38%) in January. Langurs ate 52 plant species throughout the year. The largest number of plants (6) were species of Moraceae, and langurs spent more feeding time (20%) on them alone. The number of plants eaten per month varied significantly (p < 0.05). Langurs ate Gmelina arborea, Albizzia lucida, Ficus glomereta, and Makania micrantha throughout the year. They spent 44% of their feeding time in terminal canopies and their average feeding height was 30–35 m. This is the first study to examine the feeding ecology of capped langurs and provides baseline data for the species.     

Feeding Competition and Group Size in Alouatta pigra

Researchers consider group size in primates to be determined by complex relationships among numerous ecological forces. Antipredator benefits and better resource defense are the primary pressures for large groups. Conversely, intragroup limited food availability, can result in greater intragroup feeding competition and individual energy expenditure in larger groups, creating energetic advantages for individuals in small groups and placing an upper limit group size. However, the extent to which food availability constrains group size remains unclear for many species, including black howlers (Alouatta pigra), which ubiquitously live in small social groups (≤10 individuals). We studied the relationship between group size and 2 key indices of feeding competition—day journey length and activity budgets—in 3 groups of wild Alouatta pigra at a hurricane-damaged site in Belize, Central America. We controlled for differences in food availability between home ranges (food tree density) and compared both indicators of feeding competition directly with temporal variation in food availability for each group. Our results show no consistent association between resource availability, group size, and either index of competition, indicating that feeding competition does not limit group size at the site—i.e., that larger groups can form without increased costs of feeding competition. The results support the search for other explanations, possibly social ones, for small group size in the primates, and we conclude with suggestions and evidence for such alternative explanations.     

The effect of group size on space use and aggression at a concentrated food source in blue gouramis, Trichogaster trichopterus (Pisces: Belontiidae)

Synopsis We examined how spatial distribution and the use of aggressive behavior by blue gouramis, Trichogaster trichopterus (Belontiidae), in the presence of a concentrated food source were affected by group size and by the short-term presence and absence of food. Gouramis aggregated in the area of the food source, and the frequency of aggressive acts per fish was higher for fish near the food source than for fish away from it. The frequency of aggressive acts per fish near the food source decreased with group size and was about 50 times higher in groups of 2 and 4 than it was in groups of 16 and 32. In group sizes 2 and 4, the frequency of aggression was unaffected by the presence and absence of food, but in larger group sizes aggression increased during short intervals without food. The mean proportion of time spent near the food source increased from group size 2 to group size 8 and decreased from group size 8 to group size 32 and was greater during intervals of food availability than during intervals in which food was not available. We suggest that gouramis adjust their relative use of contest and scramble competition according to the costs and benefits of aggression as determined by the number of competitors and by the potential for missed feeding opportunities. The average proportion of time spent in the vicinity of the food source appears to be influenced by both the rate of aggression and by the net rate of gain available.     

You are Not Welcome: Social Exchanges between Female Spider Monkeys (<Emphasis Type="Italic">Ateles geoffroyi</Emphasis>)

Group living leads to competition for food between group members. Two types of intragroup food competition may occur: scramble competition, in which all group members use the same resource, such that feeding opportunities are equal for everyone; and contest competition, in which some group members monopolize resources through aggression and dominance. In species in which females disperse from the natal group and immigrate into other groups, immigrant females increase group size and thus possibly food competition. Under these circumstances, other females may use aggression to discourage new females from joining the group. We assessed the distribution of aggression, embraces, and kisses among female spider monkeys (Ateles geoffroyi) in relation to group tenure. We recorded social interactions during 1688 10-min focal animal samples on 11 females in Santa Rosa, Costa Rica. We found that aggression was rare between long-term resident females and aggression rates were not higher during feeding than in other contexts, suggesting there was little contest competition. Long-term residents and less recently immigrant females showed higher aggression rates toward the most recent immigrants than toward other females, especially during the first months after a female immigrated, which coincided with the dry season. We did not find similar patterns for embrace and kiss. These results suggest that other females target aggression toward the most recent immigrants to reduce scramble competition. This finding suggests that group tenure should be included in socioecological models for species with female dispersal.     

Effects of habitat disturbance on the behavioral ecology and demographics of the Tana river red colobus (Colobus badius rufomitratus)

Annual surveys in 1985–1987 revealed that, since 1975, the total population of the Tana River red colobus (Colobus badius rufomitratus)declined by approximately 80%. An intensive study in 1986–1988 of two groups of colobus in the Tana River Primate National Reserve indicated that habitat disturbance from the changing river course and shifting agricultural practices were primarily responsible for the decline. Clearcutting around Mchelelo forest in the late 1960s compressed colobus populations to levels probably above the carrying capacity. Between 1975 and 1986 primate population density declined dramatically, the number of red colobus groups in Mchelelo forest decreased by half, and the size of the remaining group was greatly reduced. In 1986, there were fewer solitary colobus and small parties in the forest, harem male takeovers did not occur, infant survivorship increased, and demographic parameters generally had improved. The colobus groups in Mchelelo in 1973–1975, living at higher densities, showed different feeding and ranging behaviors than 1986–1988 groups. Range size was smaller in 1975, range overlap occurred, and a greater portion of the forest was used per day and per month. Mature leaves accounted for a much higher proportion of the diet. Time spent feeding and resting was the same in both studies. Social organization in predominantly one- male groups was maintained and adult and subadult females transferred between groups.     

Factors underlying party size differences between chimpanzees and bonobos: a review and hypotheses for future study

Differences in party size and cohesiveness among females have been primary topics in socio-ecological comparisons of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). This paper aims to review previous studies that attempted to explain these differences and propose some hypotheses to be tested in future studies. Comparisons of recent data show that relative party size (expressed as a percentage of total group size) is significantly larger for bonobos than chimpanzees. Although the prolonged estrus of females, close association between mother and adult sons, female social relationships including unique homosexual behavior, and high female social status might be related to the increased party size and female cohesiveness of bonobos, these social and behavioral factors alone do not appear to explain the differences between the two species. Differences in ecological factors, including fruit-patch size, density of terrestrial herbs, and the availability of scattered foods that animals forage as they travel between large fruit patches could also contribute to the differences between chimpanzees and bonobos. However, these factors cannot fully account for the increased party size and female cohesiveness of bonobos. The higher female cohesiveness in bonobos may be explained by socio-ecological systems that reduce the cost in feeding efficiency incurred by attending mixed-sex parties. These systems may include female initiatives for party ranging movements as well as the factors mentioned above. Because of their geographical isolation, the two species probably evolved different social systems. Chimpanzees, whose habitats became very dry during some periods in the Pleistocene, likely evolved more flexible fission–fusion social systems to cope with seasonal and annual variation in food availability. On the other hand, bonobos had a large refugia forest in the middle of their range even during the driest periods in the Pleistocene. Therefore bonobos, whose habitats had more abundant food and smaller variation in food availability, probably evolved systems that help females stay in mixed parties without incurring large costs from contest and scramble competition.     

Aspects of Male Competition in <Emphasis Type="Italic">Colobus vellerosus</Emphasis>: Preliminary Data on Male and Female Loud Calling,and Infant Deaths After a Takeover

Male Colobus vellerosus are the main participants in intergroup encounters, and lead incursions in neighboring groups during which they attack infants. Extragroup copulations, all-male groups, and male takeover occur in the species. Here, we provide additional information on behaviors associated with male reproductive competition in Colobus vellerosus. We examined 1 resident male loud calling and participation in intergroup encounters in relation to a takeover. We also report a second case of takeover that led to the death of the former resident male and the death of 2 male infants, presumably as a result of aggression from the all-male group. The new resident male wounded the third infant of the group, which apparently died after its mother abandoned it. During the period characterized by the attacks on the infant and after its disappearance, females initiated and participated in loud call bouts with the new resident male. We examine the possible functions of female loud calling, and suggest that in this context, it might force the resident male to call along to indicate his presence.     

Effect of Group Size on Time Budgets of Sichuan Snub-Nosed Monkeys (Rhinopithecus roxellana) in Shennongjia National Nature Reserve, China

Group size influences intragroup scramble competition, which in turn influences time budgets in some primates, and may impact age–sex classes differently. There is a great deal of debate about whether folivorous primates, e.g., colobines, experience significant feeding competition. Unlike most colobines, Sichuan snub-nosed monkeys (Rhinopithecus roxellana) live in extraordinarily large groups and eat mainly lichens supplemented by seasonal plant food. We examined the effect of group size on time budgets in this species by studying two groups of different sizes in the same habitat in Shennongjia National Nature Reserve, China (study periods: August 2006–July 2008 for the larger group, November 2008–July 2009 for the smaller group). Results showed that the distribution of activities throughout the day did not differ between groups, but that time budgets did differ. Specifically, the monkeys spent more time moving and less time resting in the larger group than in the smaller group. Intergroup comparisons for each age–sex class indicated that adult females (but not adult males or juveniles) in the larger group spent more time moving and less time resting, and tended to spend more time feeding compared to those in the smaller group. The results suggested that increased scramble competition was occurring for adult females in the larger group. We provided preliminary evidence for the existence of intragroup scramble competition in Rhinopithecus roxellana.     

Exclusive core areas and intrasexual territoriality in Eurasian red squirrels (<Emphasis Type="Italic">Sciurus vulgaris</Emphasis>) revealed by incremental cluster polygon analysis

When animal home ranges overlap extensively in species lacking overt territorial behaviours, identifying exclusive core areas within individual ranges can be difficult. By analysing the size and overlap of successively smaller core areas among individual Eurasian red squirrels (Sciurus vulgaris), we determined exclusive areas within the home ranges of resident males and females. Possible effects of habitat composition and food supplies were explored by monitoring squirrels in different conifer forests and during years with low and high tree seed production. Using outlier-exclusive cores (OEC) revealed that the total ranges consisted of large sally zones (on average, 35% of the total minimum convex polygon [MCP] range) around home ranges with multi-nucleate cores. The mean OEC home range size did not differ between the sexes but was larger with poor food availability. Home ranges (99% incremental cluster polygons [ICP]) overlapped extensively between sexes (average overlap high food–low food: males by females 21–40%, females by males 43–45%) and among males (males by males 26–44%), while intrasexual overlap among females was low (9–10%). The overlap of inner cores among females rapidly approached zero, suggesting the intrasexual territoriality of 75% core areas. This was not the case among male squirrels, for which intrasexual overlap averaged only 4% at 50% but 18% at 75% core areas. Even the smallest inner cores had some degree of intersexual overlap, indicating that complete territoriality did not occur in this species. Female home ranges were more strongly affected by annual fluctuations in food supplies than male ranges. Females reduced the size of their food-based intrasexual territories when food availability increases. Males probably benefit from using larger home ranges and core areas, which overlap with the ranges of several females, by increasing their probability of successful mating.     

Testicular Volume and Reproductive Status of Wild <Emphasis Type="Italic">Callithrix jacchus</Emphasis>

The social relationship dynamic among callitrichid females is well known. Breeding exclusivity by dominant females involves female-female competition, usually resulting in the inhibition of subordinate reproduction. However, the strategies to maintain the male breeding position are still unclear. Researchers have observed no overt aggression between males, and differences in testosterone levels between dominant and subordinate individuals do not correlate with differences in reproductive success. In Callithrix monogamy is the predominant mating system, and testicular size is compatible with the absence of sperm competition. We analyzed testicular volume during development in 95 individuals at different ages (infant n = 12, juvenile n = 9, subadult n = 15, and adult n = 59). We also investigated if the ratio between testicular volume and body mass correlates with breeding position in the social group. The ratio was significantly higher in breeding males and a positive correlation between body mass and testicular volume is significant only for nonbreeding males. The findings suggest that testicular size varies with male reproductive status in the social group and that the enlargement of testicular volume in breeding common marmoset males seems to be a result of proximate causes and to depend on social and reproductive contexts acting together or separately.     

Time–activity budget of greater rheas (Rhea americana, Aves) on a human-disturbed area: the role of habitat, time of the day, season and group size

The aim of this study was to evaluate activity–time budget, habitat use and how seasonality and group size influence the expression of greater rhea behaviours. Greater rheas are threatened South American birds; habitat loss, predation and hunting are the main factors responsible for population declines. The study was conducted in farmlands within a matrix of commercial Eucalyptus plantation and remnants of natural habitats of cerrado vegetation (savannah-like) in southeastern Brazil. Rhea groups were located visually in different habitats visited monthly from January 2004 to December 2005. Time spent searching greater rheas in each habitat was equally distributed. Data were collected using scan sampling with instantaneous recording of behaviours every minute. The time–activity budget of greater rheas was influenced by habitat structure, time of the day, season and group size. Rheas spent more time in open areas than in forested areas (p < 0.001). Vigilance behaviours were more displayed in forested areas, in the dry season and by solitary and small groups of birds. Resting behaviours occurred more often in open lands and within groups with more than three rheas. Food availability, good visibility and low human presence are the possible factors for the preference of greater rheas for pasturelands. The results support the resource availability hypothesis, where it is expected that habitats with a higher food availability will be more used by the animals, group size hypothesis, where the scarcity of resources will lead to smaller groups of animals and that forestry modifies greater rheas habitat use and behaviours.     

Interference competition and group size effect in sika deer (<Emphasis Type="Italic">Cervus nippon</Emphasis>) at salt licks

Competition has long been considered as a confounding factor of group size effect but the understanding of interference competition is rudimentary for the difficulty in disentangling interference competition from scramble competition adequately. Here, we analysed remote-camera video records of wild sika deer (Cervus nippon) at salt licks in southern China from March 1, 2006 to November 30, 2008 to investigate how interference competition and predation risk interacted on vigilance behaviour. Scramble competition is negligible at salt licks; therefore, we could focus our interest in interference competition. We used linear mixed model to compare vigilance, licking and aggression behaviours among females with and without fawn as well as males with different group sizes to identify the primary role of vigilance behaviour in sika deer. In total, 168 individuals were recorded and observation time was 2,733.04 min. We found that deer spent much time on vigilance and scanned frequently in spring and winter, and females with fawn spent more time on vigilance than females without fawn, suggesting vigilance for predation risk. Aggression ratio increased first and then decreased, while scan frequency continued to decline and then slightly increased when group size increased from two to seven, implying vigilance for interference competition. Our results suggested vigilance in sika deer was influenced by both predation risk and interference competition, but was mainly driven by predation risk even at sites with intense interference competition. Our results of interference competition shed some light on finding the underlying mechanism of group size effect in wild populations.     

Sexual,Seasonal and Group Size Differences in the Allocation of Time between Vigilance and Feeding in the Greater Rhea,Rhea americana

We studied the effect of sex and group size on the proportion of time a greater rhea, Rhea americana, allocates to vigilance and feeding during the breeding and the non-breeding seasons. We analysed 175 records of focal animals that were feeding alone or in groups of 2 to 26 birds. In both seasons, males spent more time in vigilance and less time in feeding than females. Both sexes spent more time in vigilance and less time in feeding during the breeding season. Sexual and seasonal differences in vigilance were the result of different mechanisms. Males had shorter feeding bouts than females but there were no sexual differences in the length of the vigilance bouts. On the contrary, seasonal differences were the result of males and females having longer vigilance bouts during the breeding season but there were no seasonal differences in the length of the feeding bouts. During the non-breeding season, individual vigilance was higher in rheas foraging alone than in groups. In this case, solitary birds had longer vigilance and shorter feeding bouts than birds foraging in groups. We discuss the possible effect of intragroup competition and food availability on the allocation of time between feeding and vigilance in this species.     

Patch depletion behavior differs between sympatric folivorous primates

Food competition in group-living animals is commonly accepted as a critical determinant of foraging strategies and social organization. Here we examine food patch depletion behavior in a leaf-eating (folivorous) primate, the guereza (Colobus guereza). Snaith and Chapman (2005) studied the sympatric folivorous red colobus (Procolobus rufomitratus), which shares many food resources with the guereza. They determined that red colobus deplete the patches (feeding trees) they use, while we found contrary evidence for guerezas using the same methods. We found that the time guerezas spent feeding in a patch was affected by neither tree size, an indicator of food abundance, nor the size of the feeding group, an indicator of feeding competition. For their principal food item (young leaves), intake rate remained constant and coincided with a decrease in the distance moved to find food within a patch, implying that guerezas do not deplete patches. This points to a fundamental difference in the use of food by guerezas and red colobus, which may be linked to the large difference in their group sizes and/or to a disparity in their digestive physiologies. However, further analyses revealed that the number of feeders within a patch did not affect patch depletion patterns in either species, leaving the potential for a physiological basis as the most plausible explanation. Our research highlights the need for a more critical examination of folivorous primate feeding ecology and social behavior, as all folivorous primates are typically lumped into a single category in socioecological models, which may account for conflicting evidence in the literature.