Home range structure and inter-group competition for land of Japanese macaques in evergreen and deciduous forests

The per capita home range area of Japanese macaques,Macaca fuscata, is significantly smaller in evergreen forest than in deciduous forest, though a corresponding difference in food resource utilization patterns has never been described. The present study compared the home range utilization pattern of Japanese macaques living in two habitats: the Yakushima population inhabits an evergreen forest, while the Kinkazan population inhabits a deciduous forest. We found that in the Yakushima population, (1) food density was higher; (2) inter-feeding bout sites distance was shorter; (3) daily travel distance was shorter; (4) home range size was smaller; and (5) the unit value of the main home range was higher, than in the Kinkazan population. Yakushima groups utilized a small home range area intensively, compared to Kinkazan groups. We also found that a Yakushima group shared 24% of its main home range with neighboring groups, though a Kinkazan group shared only 10% with other groups. It is supposed that food distribution affects daily ranging pattern, and ultimately the social relationships between groups in Japanese macaques.     

Seasonal Variations in the Diet and Feeding Effort of Two Groups of Howlers in Different Sized Forest Fragments

Little is known about how resource limitation affects the feeding ecology of primates in forest fragments. Here, we describe seasonal variation in the diet and feeding effort of 2 groups (RH and RC3) of howlers (Alouatta palliata mexicana) living in different sized forest fragments in Los Tuxtlas, Mexico. The RH group, which lived in a larger and more preserved forest fragment, with a higher availability of fruit and Ficus trees, had a higher and more constant consumption of fruit throughout the study year. Moreover, this group fed from larger food sources, i.e., trees, lianas, and shrubs, and spent more time feeding from each food source. The feeding effort, defined as the time spent feeding and traveling divided by time spent resting, of the RH group was also significantly lower and more stable than that of the RC3 group throughout the study year. As feeding effort has been positively related to stress in primates, such increases in feeding effort could have negative consequences for howlers in small or degraded forest fragments. Our study suggests that habitat characteristics interact with plant seasonality to determine the diet and feeding effort of howlers in forest fragments and that groups living in small and degraded forest fragments may be particularly vulnerable to years of low fruit production.     

Ecology of the Zanzibar Red Colobus Monkey: Demographic Variability and Habitat Stability

We examined the Zanzibar red colobus' (Procolobus kirkii) social structure and population dynamics in relation to the density, diversity and dispersion of food resources in ground-water forest and agricultural land, which we characterized in terms of red colobus food species density, diversity, basal area and dispersion. We used transect sampling and group follows to describe population dynamics and social systems. Two agricultural areas, SJF Shamba and Pete Village, had higher densities and more uniformly dispersed red colobus food tree species than those of the ground-water forest. Red colobus at these two sites had greater population densities and natality, and smaller home ranges than red colobus in the ground-water forest. However, these findings apply to a very small area of agricultural land (approximately 18 ha) that is contiguous with an area of the forest reserve having a high density of red colobus. It is not representative of agricultural areas elsewhere on Zanzibar which support much lower densities or no red colobus. Although agricultural areas contiguous with the forest reserve had high densities of red colobus, they appear to be very unstable. Within the agricultural areas, we observed higher intergroup variation in group size and composition, study groups that decreased dramatically in size and disappeared from the study site, significantly lower levels of juvenile recruitment, and red colobus food trees that exhibited definite signs of overbrowsing. This apparent instability in the subpopulation of red colobus utilizing agricultural systems probably reflects the lower basal area of food trees and the greater fragmentation of suitable habitat and floristic dynamics due to human activities in these areas. A fusion-fission social system occurred only in the ground-water forest subpopulation, which we hypothesize to be due to highly clumped food resources.     

Collective Vigilance in the Wintering Hooded Crane: The Role of Flock Size and Anthropogenic Disturbances in a Human‐Dominated Landscape

Vigilance achieved at the group level, known as collective vigilance, can enhance the ability to assess threats and confer benefits to gregarious prey species. Examining the factors that influence collective vigilance and exploring how individual vigilance is organized at the group level can help to understand how prey groups respond to potential threats. We quantified collective vigilance and determined its temporal pattern in a natural wintering population of the hooded crane Grus monacha in the Shengjin Lake reserve in China. We examined the role of flock size and anthropogenic disturbances in the human‐dominated landscape on collective vigilance and level of synchronization. The proportion of time during which at least one individual scanned the surroundings (collective vigilance) increased with flock size and was higher in the more disturbed buffer zone of the lake. Synchronization of vigilance occurred more frequently in the smaller flocks but was not related to the risk of disturbance. Synchronization implies that individuals tend to monitor and copy the vigilance of neighbors. In the degraded wetlands, the wintering hooded crane benefits from foraging in groups and synchronizing their vigilance in response to human disturbances.     

Monkey Abundance and Social Structure in Two High-Elevation Forest Reserves in the Udzungwa Mountains of Tanzania

The effects of human activity on population and social structure are a pantropical concern for primate conservation. We compare census data and social group counts from two forests in the Udzungwa Mountains, Tanzania. The main aim is to relate differences within and between the forests to current theory on the effect of human disturbance on primate abundance and group size. The survey reveals the presence of the restricted-range red colobus, Procolobus gordonorum, in New Dabaga/Ulangambi Forest Reserve (NDUFR). The primate community of NDUFR is impoverished compared to that in Ndundulu forest. Red colobus and black-and-white colobus (Colobus angolensis palliatus) abundance and group size are lowest in NDUFR. Fission-fusion of red colobus social groups may be occurring in previously logged areas of both forests. Our observations are consistent with current theory on the effect of habitat degradation and hunting on primates, but the relative effects of the 2 factors could not be differentiated. We pooled the results with previous data to show that abundance of red colobus in the Udzungwa Mountains is lowest at high elevations. Low red colobus group sizes appear to be related to human activity rather than elevation. Black-and-white colobus and Sykes monkeys (Cercopithecus mitis) show no relationship with elevation. Future studies will require more detailed information on vegetation, diet and ranging patterns to interpret fully intraspecific variation in population demography and social structure in the Udzungwa Mountains.     

Lion-tailed macaques (Macaca silenus) in a disturbed forest fragment: Activity patterns and time budget

We describe the activity patterns and time budget of a feral group of lion-tailed macaques that were confined to a disturbed forest fragment of 65 ha and compare the results with those obtained for groups in protected forests. The degraded nature of the study site was reflected in low tree densities, low specific diversity, gaps in the girth distribution of trees, and frequent disturbance by humans. The study group of 43 subjects was twice as large as lion-tailed macaque groups in protected habitats. They spent the most time ranging (34.0%), followed by foraging (23.7%), feeding (17.9%), resting (16.0%), and other activities such as social interactions (8.4%). Monthly variations are significant for all activity categories except ranging. Times spent resting and foraging are negatively correlated (r = −0.5) and show significant seasonal differences. Foraging time was highest from September to November, when key food sources such asCullenia andArtocarpus were absent or marginally available. The study group spent most time (40.4%) at canopy levels between 21 and 30 m. They spent more time each day ranging than resting or feeding and more time terrestrially compared with groups in protected forests. Large group size, poor habitat quality, and seasonal variation in food availability were the major variables affecting their time budget, and these variables accounted for differences from the time budgets of groups in protected forests.     

Demographic Structure of Zanzibar Red Colobus Populations in Unprotected Coral Rag and Mangrove Forests

More than half of the global population of the endangered Zanzibar red colobus (Procolobus kirkii) live outside the single major protected area on Zanzibar Island. We present data on the 2 largest, discrete subpopulations living in unprotected areas at extremes of the species’ range. We compare the size and structure of 11 groups, specifically 6 core groups inhabiting interior, mature forest with 5 peripheral groups living in disturbed/degraded edge habitats. Groups living in southern mangrove forest—a species-poor but more productive and less seasonal habitat than coral rag thicket—had larger group sizes and more heterogeneous age structure, were more stable, and had higher rates of infant survival than did groups in northern coral rag. Group size ranged from 5.5 ± 1.6 SD (the smallest reported for this species) in edge coral rag to 31.2 + 1.9 SD in core mangroves. Edge groups were significantly smaller than core groups in northern coral rag while in the south, where all groups had access to mangroves, we found no significant difference in mean group size between edge and core areas. Groups using mangroves exhibited frequent social play, an indicator of habitat quality, and had a higher ratio of births per female per year. We suggest that mangroves are an important refuge and possibly source habitat for Zanzibar red colobus. We urge the conservation of mangrove and remaining coral rag in the unprotected areas described here in an effort to sustain this endemic species throughout its range.     

Demographic population structure of black howler monkeys in fragmented and continuous forest in Chiapas,Mexico: Implications for conservation

For wild primates, demography studies are increasingly recognized as necessary for assessing the viability of vulnerable populations experiencing rapid environmental change. In particular, anthropogenic changes such as habitat loss and fragmentation can cause ecological and behavioral changes in small, isolated populations, which may, over time, alter population density and demographic structure (age/sex classes and group composition) in fragment populations relative to continuous forest populations. We compared our study population of Endangered black howler monkeys (Alouatta pigra) in 34 forest fragments around Palenque National Park (PNP), Mexico (62 groups, 407 individuals), to the adjacent population in PNP, protected primary forest (21 groups, 134 individuals), and to previous research on black howlers in fragments in our study area (18 groups, 115 individuals). We used χ² and Mann–Whitney U tests to address the questions: (a) what is the current black howler demographic population structure in unprotected forest fragments around PNP? (b) How does it compare to PNP's stable, continuous population? (c) How has it changed over time? Compared to the PNP population, the fragment populations showed higher density, a significantly lower proportion of multimale groups, and significantly fewer adult males per group. The population's age/sex structure in the fragmented landscape has been stable over the last 17 years, but differed in a higher proportion of multifemale groups, higher density, and higher patch occupancy in the present. In the context of conservation, some of our results may be positive as they indicate possible population growth over time. However, long-term scarcity of adult males in fragments and associated effects on population demographic structure might be cause for concern, in that it may affect gene flow and genetic diversity. The scarcity of adult males might stem from males experiencing increased mortality while dispersing in the fragmented landscape, whereas females might be becoming more philopatric in fragments.     

Links between habitat degradation,and social group size,ranging, fecundity,and parasite prevalence in the Tana River mangabey (Cercocebus galeritus)

We investigated the effects of anthropogenic habitat degradation on group size, ranging, fecundity, and parasite dynamics in four groups of the Tana River mangabey (Cercocebus galeritus). Two groups occupied a forest disturbed by human activities, while the other two occupied a forest with no human disturbance. We predicted that the groups in the disturbed forest would be smaller, travel longer distances daily, and have larger home ranges due to low food tree abundance. Consequently, these groups would have lower fecundity and higher parasite prevalence and richness (number of parasite species). We measured the abundance of food trees and anthropogenic activity in the forests, the groups' daily travel distances and home range sizes, and censused social groups over 12 months. We also analyzed fecal samples for gastrointestinal parasites from three of the groups. The disturbed forest had a lower abundance of food trees, and groups in this forest traveled longer distances, had larger home range sizes, were smaller, and had lower fecundity. The groups in the disturbed forest had higher, although not statistically significant, parasite prevalence and richness. This study contributes to a better understanding of how anthropogenic habitat change influences fecundity and parasite infections in primates. Our results also emphasize the strong influence of habitat quality in determining daily travel distance and home range size in primates. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Behavioral modifications in northern bearded saki monkeys (<Emphasis Type="Italic">Chiropotes satanas chiropotes</Emphasis>) in forest fragments of central Amazonia

We investigated behavioral differences among seven groups of northern bearded saki monkeys (Chiropotes satanas chiropotes) living in five forest fragments and two areas of continuous forest at the Biological Dynamics of Forest Fragments Project study area, located approximately 80 km north of Manaus, Brazil. We collected data in six research cycles from July–August 2003 to January 2005–April 2006. When bearded saki monkeys were present in a study area, we followed the group from dawn until dusk for three consecutive days. Every 5 min, we conducted behavioral scans of all visible individuals. There was a positive relationship between forest size and group size, but animals in the small forest fragments lived at greater densities. Bearded saki monkeys in the smaller fragments spent more time resting, less time traveling, and less time vocalizing, but there was no relationship between forest size and the amount of time spent feeding. Our results indicate that the main behavioral differences among the groups are related to the amount of forest resources (e.g., fruit trees, space) available to the monkeys in the smaller fragments, as well as the resulting smaller group sizes. We stress the need to preserve large tracts of forest and provide connectivity between forest patches.     

Competing pressures on populations: long-term dynamics of food availability,food quality,disease, stress and animal abundance

Despite strong links between sociality and fitness that ultimately affect the size of animal populations, the particular social and ecological factors that lead to endangerment are not well understood. Here, we synthesize approximately 25 years of data and present new analyses that highlight dynamics in forest composition, food availability, the nutritional quality of food, disease, physiological stress and population size of endangered folivorous red colobus monkeys (Procolobus rufomitratus). There is a decline in the quality of leaves 15 and 30 years following two previous studies in an undisturbed area of forest. The consumption of a low-quality diet in one month was associated with higher glucocorticoid levels in the subsequent month and stress levels in groups living in degraded forest fragments where diet was poor was more than twice those in forest groups. In contrast, forest composition has changed and when red colobus food availability was weighted by the protein-to-fibre ratio, which we have shown positively predicts folivore biomass, there was an increase in the availability of high-quality trees. Despite these changing social and ecological factors, the abundance of red colobus has remained stable, possibly through a combination of increasing group size and behavioural flexibility.     

Inter‐group variability in seed dispersal by white‐handed gibbons in mosaic forest

Seed dispersers, like white‐handed gibbons (Hylobates lar), can display wide inter‐group variability in response to distribution and abundance of resources in their habitat. In different home ranges, they can modify their movement patterns along with the shape and scale of seed shadow produced. However, the effect of inter‐group variability on the destination of dispersed seeds is still poorly explained. In this study, we evaluate how seed dispersal patterns of this arboreal territorial frugivore varies between two neighboring groups, one inhabiting high quality evergreen forest and one inhabiting low quality mosaic forest. We predicted a difference in seed dispersal distance between the two groups (longer in the poor quality forest). We hypothesized that this difference would be explained by differences in home range size, daily path length, and ranging tortuosity. After 6 months of data collection, the evergreen group had a smaller home range (12.4 ha) than the mosaic group (20.9 ha), significantly longer daily path lengths (1507 m vs. 1114 m respectively) and greater tortuosity (39.1 vs. 16.1 respectively). Using gut passage times and displacement rates, we estimated the median seed dispersal distance as 163 m for the evergreen group (high quality forest) and of 116 m for the mosaic group (low quality forest). This contradiction with our initial prediction can be explained in term of social context, resource distribution, and habitat quality. Our results indicate that gibbons are dispersers of seeds between habitats and that dispersal distances provided by gibbons are influenced by a range of factors, including habitat and social context.     

Alarm Calling and Implications for Risk Perception in a Desert Baboon Population

Patterns of alarm calling and their implications for perceived predation risk were explored among adult baboons Papio cynocephalus ursinus in four social groups differing in both size and composition (22–55 members with one to six adult males) in a desert population. Data were collected in a field experiment where alarm calls were elicited from baboons under similar conditions of risk in response to the approach of a potential predator, a human observer. The results show that females call more frequently than males in most groups. In addition, the median calling rate of females shows an exponential increase in smaller groups. These patterns suggest that females in small groups may perceive the highest risk in this population. Nevertheless, there was no clear tendency for either sex to be the first to call. The observer approaches were also used to evaluate the influence of group size on the ease of detection of 1. the baboons by the observer; and 2. the observer by the baboons. Group size did not appear to affect detection distances for either subject, although the probability that baboons were more likely to perform alarm calls before the observer had detected them increased in smaller groups.     

The potential of paleoecology for functional forest restoration planning: lessons from Late Holocene Italian pollen records

We describe forest landscape transformations during the last two millennia in the Italian peninsula by analyzing local (Rieti basin – Lago Lungo) and regional (RF93-30 Adriatic Sea) sediment cores. We identify a dynamic forest ecosystem through paleoecologic reconstruction and consider potential interventions for effective restoration of the most ancient, least disturbed forest ecosystem. The most degraded ecosystems in consequence of human activities were hygrophilous (wet) and mesic forests. In the Rieti Basin, degraded forest ecosystems on mountain slopes are undergoing some degree of forest succession and have less need of restoration. However, management plans for biodiversity, ecosystem services and resources conservation are needed to achieve more sustainable development. In Rieti, the paleoecological investigation revealed a dramatic decrease of deciduous wet and mesic tree taxa through time due to human landscape transformation. The starting point for restoration of a Mediterranean forest ecosystem that preserves natural biodiversity and associated ecosystem services requires recreating some portion of the floodplain wetland ecological niche. Once floodplain forest ecological niche has been recreated, the original ecosystem composed of Alnus, Fraxinus excelsior, Tilia spp., Carpinus betulus and Acer spp., all species which today are rare, should be planted on the basis of microsite characteristics and tree autoecology.     

Fragmentation causes rarity in common marmosets in the Atlantic forest of northeastern Brazil

The purpose of this study was to investigate the population status of the common marmosets, Callithrix jacchus, in one of their main habitats, the northeastern Atlantic forest of Brazil, where only 2% of its original area remains as small and isolated forest fragments, to determine long-term viable populations. The study was carried out in 15 forest fragments, measuring from 3,478.3 ha (the largest) to 6 ha, which were invariably subjected to high human impact. Line transect surveys were carried out between January 2002 and December 2004, along transects measuring from 350 to 4,000 m, between 0500 h and 0900 h. Common marmosets were registered in 73% (n = 11) of the forest fragments, were not recorded in the largest one, the Coimbra Forest, and group sizes varied from 1 to 4 individuals. A negative significant relationship was detected between the size of the fragment and the number of sightings of common marmosets. It is shown that the number of groups of common marmosets dwelling in this highly impacted landscape is nowadays lower than necessary for long-term survival. Additionally, smaller fragments having more groups suggests that they live in total association with humans, which assure their subsistence through the supply of introduced and exotic foods.     

Variability in habitat, diet, and social structure of Hapalemur griseus in Ranomafana National Park, Madagascar

This study investigated the effects of habitat on the diet, population density, and social structure of a small-bodied folivore, Hapalemur griseus. Three groups of H. griseus were followed at two study sites (Tala and Vato) within Ranomafana National Park in southeastern Madagascar. These two sites differed in degree of habitat disturbance, forest composition, and forest structure, as determined by botanical plots (50 x 10 m) which were monitored twice monthly in the home ranges of three study groups (group T, n = 4; group V1, n = 4; group V2, n = 2). Tala has experienced more habitat disturbance compared to Vato, and this appeared to influence population density and group size. The H. griseus that inhabit Tala occur at much higher densities and in larger social groups than the H. griseus at Vato. These results may be attributable to: 1) a greater number of potential food sources, 2) a more dense resource base, and/or 3) higher-quality resources at Tala for this folivore. In general, dietary diversity for all groups was low, and groups exploited similar plant species. However, within this small range of food sources, each study group specialized in food sources found in the highest abundance within their home range. This resulted in dietary differences between groups within sites, as well as differences between sites. Introduced tree species such as Chinese guava (Psidium cattleyanum) may have greatly impacted the diet and social structure of those groups at Tala, whose home ranges included this food source. In contrast, Vato group 1 ingested more new and mature leaves of Ficus spp., and Vato group 2 primarily ate spider bamboo (Nastus elongatus). In conclusion, it seems that microhabitat differences, which may be related to habitat disturbance and/or other factors such as topography, influenced the food species ingested by H. griseus. Overall habitat quality, which is likely also affected by habitat disturbance, influenced general diet, population density, and group size.     

Food conditions, competitive regime, and female social relationships in Japanese macaques: within-population variation on Yakushima

Feeding conditions, competitive regime, and female social relationships of Japanese macaques (Macaca fuscata) on Yakushima were compared between the two habitats at two different altitudes (coniferous forest, 1,000–1,200 m and coastal forest, 0–200 m). Fruit availability was higher in the coastal forest. There was no consistent difference in the frequency of agonistic interactions within a group during feeding between the two habitats. The coastal forest evoked stronger inter-group contest competition compared to the coniferous forest as evidenced by a higher inter-group encounter rate and a higher proportion of aggressive encounters to non-aggressive ones. Birth rate was higher in larger groups compared to smaller ones in the coastal forest, but did not differ in the coniferous forest. In spite of these differences in competitive regime, no variation in female social relationships was observed, such as direction and concentration on particular individuals in grooming, linearity in dominance rank, counter-attack, and support of juvenile kin during agonistic interactions. The present results indicate that the female social relationships of Japanese macaques are robust and do not change according to changes in the current environment.     

Arthropod Diversity in Lama Forest Reserve (South Benin), a Mosaic of Natural, Degraded and Plantation Forests

Arthropod assemblages were examined in Lama forest reserve, a protected area situated in the Dahomey gap, southern Benin, composed of plantations, degraded forest and remnants of natural forest. The objectives were to compare assemblages in relation to forest type and use, to elucidate the value of forest plantations for biodiversity conservation and to identify indicator species for specific forest habitats. Arthropods were collected over an 11-month period, using standardized sets of traps (pitfall, emergence, Malaise and flight intercept traps). Nine different habitats were studied, including natural and degraded forest, forest plantations (Tectona grandis and Senna siamea) of different age, and isolated forest fragments. Our analysis focused on detritivorous and xylophagous arthropods but also included ground beetles and heteropterans, totalling 393 species. We found no differences in species richness among natural and degraded forest habitats in the centre of the reserve (Noyau central). Outside of the Noyau central, species richness was highest in old teak plantations and isolated forest fragments and lowest in young teak and fuelwood plantations. Detrended correspondence analysis (DCA) separated three main groups: (1) natural forest, (2) degraded forest and young plantations, and (3) old plantations and isolated forest fragments. Multiple regression of DCA scores of the first two axes on environmental variables identified one natural and three disturbance-related predictors of arthropod assemblages in Lama forest: soil type (texture), canopy height, naturalness (proportion of Guineo-Congolian plant species) and understorey vegetation cover. We identified 15 indicator species for six different forest habitats. The highest numbers were found in abandoned settlements and old teak plantations. β-diversity was similar among the three DCA ordination groups (degraded forest excluded). Values for β-diversity were relatively high, suggesting that all major forest habitats contribute significantly to regional species pools and should therefore be protected. To enhance arthropod diversity, we propose that management practices in Lama forest should aim to encourage the development of species-rich understorey vegetation of the Guineo-Congolian phytogeographical region.     

Long-term dynamics of wild primate populations across forests with contrasting protection in Tanzania

Anthropogenic activities driving tropical forests' loss imperil global biodiversity and provision of ecosystem services. In this context, systematic monitoring programs evaluating wildlife trends are essential. Non-human primates are relevant conservation targets since they represent vital components of tropical forests by serving as pollinators and seed dispersers. Here, we present primate group counts data collected over 19 years in a primate hotspot in Tanzania. We analyzed data with a hierarchical dynamic model accounting for imperfect detection that estimates local group abundance and temporal rates of change, to assess whether habitat protection explained trends of the arboreal and diurnal Peters' Angola colobus (Colobus angolensis palliatus), Udzungwa red colobus (Piliocolobus gordonorum), and Tanzania Sykes' monkey (Cercopithecus mitis subsp. moloneyi). We targeted populations occurring in two forest blocks with contrasting protection regimes, with one block impacted by targeted poaching of the two Colobus species. We found that these latter species were much less abundant in the more human impacted forest, underwent a rapid decline, and subsequently remained at low abundance and without signs of recovery once this forest was granted greater protection. Instead, Sykes' abundance did not differ between forests, and improved protection was associated with a slight increase in abundance. Age class composition for social groups of both Colobus species differed between forests, indicating altered births and survivorship rates in the impacted forest. Results suggest that targeted hunting can prevent recovery for several years and even after increased habitat protection. Our approach appears valuable to monitor population dynamics over the long term, highlighting species-specific variations in both vulnerability to anthropogenic disturbance and recovery patterns in primate populations.     

Demography, range use, and behavior in black lemurs (Eulemur macaco macaco) at Ampasikely, northwest Madagascar

We studied a black lemur population over a 2-year period (1992-1993) and 8 years later (2000) in a 50-ha secondary forest in northwest Madagascar. All of the animals were marked to investigate population dynamics and seasonal variation in ranging and behavior, and new data on black lemurs were obtained. Our data on demographic characteristics were expanded to include other forest sites and contrasted with those collected in other Eulemur macaco macaco field studies, in relation to human activity and the presence of introduced and cultivated plant species. Density is affected by deforestation and hunting. Group size and home range depend on the composition of the forest and probably food patches. Sex ratio at birth varies according to the number of females per group, a result that fits the local resource competition model. Groups are multimale-multifemale, and adult females form the core of the groups. Reproductive parameters indicate sharply defined seasonal breeding, a high female reproductive rate, and birth synchrony. Changes in group composition reveal male and female juvenile dispersal, male transfer between groups at the time of mating, and adult female transfer and group fission when groups exceed a critical size. At mating and birth, intergroup agonistic encounters occurred at home-range boundaries, and larger groups were dominant over smaller groups. Patterns of intragroup interactions suggest that males compete for access to groups of females during the mating season, and that females may compete for food resources during the birth season. Our study also reports female social dominance and lack of sexual weight dimorphism in this species.