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

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.     

Within-group social relationships among females and adult males in wild western lowland gorillas (Gorilla gorilla gorilla)

Within-group female relationships, and relationships between females and adult males have not been described for wild western lowland gorillas. New data are presented here from Mbeli Bai in the Nouabale-Ndoki National Park, Republic of Congo. Nine groups were observed over a continuous 2-year period, and affiliative and agonistic interactions, as well as time spent by females and adult males in proximity to each other were recorded. Affiliative behavior was extremely rare in the bai, and measures of proximity between individuals were inconclusive because of the small sample sizes. Rates of agonistic interaction among females were highly variable between groups. The majority of agonistic interactions were undecided, and the supplant rate was low. Evidence for an agonistic dominance hierarchy is weak. The data do not support hypotheses that increased frugivory in western lowland gorillas raises levels of within-group contest competition; however, the need for intersite comparisons is stressed. In contrast, rates of agonistic behavior between females and silverback males were higher and more consistent between groups. Agonistic relationships between males and females conformed with patterns seen in mountain gorillas, where male protection from intraspecific aggression is important. The benefit females gain by forming long-term cooperative alliances appears to be small, and is likely outweighed by reproductive advantages associated with male protection.     

Individual space use strategies of wild juvenile Atlantic salmon

Movements of 60 stream-dwelling wild Atlantic salmon Salmo salar (97–118 mm), each tagged with a passive integrated transponder, were monitored during four trials in an enclosed section (24 m long, 45·1 m² total area) of a stream at a range of densities (four, eight, 16 and 32 fish per enclosure). Patterns of space use differed markedly between individuals, with 80% of fish establishing home ranges within 8 days of introduction to the enclosure (settlers) and the remainder continuing to move throughout the length of the enclosure (non-settlers). Although aggressive interactions were quite frequent and dominant fish were observed chasing subordinates, there was considerable overlap of home ranges of settlers at all densities; this was the case even at lower densities at which only a fraction of the enclosure was used by the fish. Thus, rather than adopting fixed territories, the salmon showed a high level of space sharing. Individual fish used the same local area in different ways, ranging from highly localized feeding on drifting food items to a wider-ranging strategy of specialising on benthic food. Among the fish that settled absolute growth rates were inversely related to body size, and at high densities fish lost weight. These results suggest that space use in wild juvenile salmon is more complex than a mosaic of territories, that salmon demonstrate significant variability in individual space use patterns, and that large fish may suffer disproportionately when populations are at the carrying capacity of their environment.     

Aspects of the ranging pattern in a group of wild woolly monkeys (Lagothrix lagothricha)

A group of woolly monkeys (Lagothrix lagothricha), studied for 1,800 hr from June 1984 until September 1987 in the eastern Colombian Amazon, used a home range of about 760 ha, 90% of which overlapped the ranges of three other groups. Home range use varied throughout the year, correlating in part with variations in fruit production. The home range exhibited a nonexclusive “core area” in the floristically most diverse part of the home range, although the majority of the home range was entered at a much lower frequency. Within the study area woolly monkeys occurred at a density of 5.5 individuals/km². The average day range was 2,880 m, and the average straight line distance between sleeping sites was 896 m. Day ranges differed significantly across months, but the only significant correlation tested was a positive relation with time spent “moving” in the activity budget. Comparisons with three other Amazonian sites where woolly monkeys have been studied reveal considerable variation. Soil fertility, plant community differences, and other factors seem to influence ranging patterns. © 1996 Wiley-Liss, Inc.     

Sex-biased dispersal in western lowland gorillas (Gorilla gorilla gorilla)

We explored two hypotheses related to potential differences between sexes in dispersal behaviour in western lowland gorillas (Gorilla gorilla gorilla). Direct observations suggest that immature females have more opportunities to move between breeding groups than immature males. The distribution of kin dyadic relationships within and between groups does not, however, support this hypothesis. At larger geographical scales, dispersal is likely to be easier for males than females because of the solitary phase most blackbacks experience before founding their own breeding group. However, previous work indicates that males settle preferentially close to male kin. By specifically tracing female and male lineages with mitochondrial and Y-chromosomal genetic markers, we found that male gorillas in the 6000 km2 area we surveyed form a single population whereas females are restricted to the individual sites we sampled and do not freely move around this area. These differences are more correctly described as differences in dispersal distances, rather than differences in dispersal rates between sexes (both sexes emigrate from their natal group in this species). Differences in resource competition and dispersal costs between female and male gorillas are compatible with the observed pattern, but more work is needed to understand if these ultimate causes are responsible for sex-biased dispersal distances in western lowland gorillas.     

Phenotypic correlates of male reproductive success in western gorillas

Sexual selection is thought to drive the evolution of sexually dimorphic traits that increase male reproductive success. Despite a large degree of sexual dimorphism among haplorhine primates, phenotypic traits that may influence the reproductive success of males are largely unstudied due to long life spans and the difficulties in quantifying such traits non-invasively. Here we employ digital photogrammetry of body length and crest size, as well as ranking of the gluteal muscle size, to test whether these sexually dimorphic traits are associated with long-term measures of male reproductive success in western gorillas. Among 19 adult male gorillas monitored for up to 12.5 years, we found that all three phenotypic traits were positively correlated with the average number of mates per male, but only crest size and gluteal muscle size were significantly correlated with offspring survival and the annual rate of siring offspring that survive to weaning age. We discuss why such sexually dimorphic traits might be under ongoing selection in gorillas and other species.     

Food transfers in immature wild western lowland gorillas (Gorilla gorilla gorilla)

The transfer of food items between individuals has been described in primates as serving an informative purpose in addition to supplementing the diet of immature individuals. This behaviour has yet to be described in western lowland gorillas (Gorilla gorilla gorilla), and results are presented here of observations of food transfers in immature gorillas at Mbeli Bai, Republic of Congo. The frequency of food transfers decreased with increasing immature age, while the frequency of independent feeding and processing of food increased. Transfers between mothers and infants were the most frequent, with infants attempting to take items from the mother. These attempts were not always successful and the item was relinquished on less than 50% of attempts. Mothers also took items from their offspring. The results point to the functional significance of food transfers in western lowland gorillas being informational. In a bai environment, where one species forms the majority of a visiting gorilla’s diet despite other species being available, the initiation of food transfers by immatures is proposed to serve the purpose of familiarising them with which species, and which parts of those species, may be eaten.     

Western lowland gorillas (Gorilla gorilla gorilla) change their activity patterns in response to frugivory

The most important environmental factor explaining interspecies variation in ecology and sociality of the great apes is likely to be variation in resource availability. Relatively little is known about the activity patterns of western lowland gorillas (Gorilla gorilla gorilla), which inhabit a dramatically different environment from the well‐studied mountain gorillas (G. beringei beringei). This study aims to provide a detailed quantification of western lowland gorillas' activity budgets using direct observations on one habituated group in Bai Hokou, Central African Republic. We examined how activity patterns of both sexes are shaped by seasonal frugivory. Activity was recorded with 5‐min instantaneous sampling between December 2004 and December 2005. During the high‐frugivory period the gorillas spent less time feeding and more time traveling than during the low‐frugivory period. The silverback spent less time feeding but more time resting than both females and immatures, which likely results from a combination of social and physiological factors. When compared with mountain gorillas, western lowland gorillas spend more time feeding (67 vs. 55%) and traveling (12 vs. 6.5%), but less time resting (21 vs. 34%) and engaging in social/other activities (0.5 vs. 3.6%). This disparity in activity budgets of western lowland gorillas and mountain gorillas may be explained by the more frugivorous diet and the greater dispersion of food resources experienced by western lowland gorillas. Like other apes, western lowland gorillas change their activity patterns in response to changes in the diet. Am. J. Primatol. 71:91–100, 2009. © 2008 Wiley‐Liss, Inc.     

The strategic use of sex in wild female western gorillas

Human females, unlike most mammals, are sexually active outside of fertile periods. This decoupling of sexual behavior from its conceptive function has had an enormous impact on human social relationships, and yet we know little about why there was selection for nonconceptive mating. Here we examine one form of nonconceptive mating, the mating that occurs during pregnancy or post‐conceptive (PC) mating, in wild western gorillas (Gorilla gorilla). Using a near complete mating record for five females during gestation, we show that pregnant females varied in the timing and frequency of mating, and used PC mating conditionally, synchronizing copulations to occur on days when other females mated, and refraining from mating for lengthy periods when no other females mated. As pregnant females mated exclusively with the same male before and after conception, and mated in response to group female (and not male) behavior, we conclude that western gorillas used PC mating as a form of female competition, and not to confuse paternity or to obtain immediate benefits from the male, as suggested earlier. The male initiated copulations preferentially with females of high rank, rather than distinguishing between pregnant and cycling females. Therefore, PC mating appears to be a strategy by which high‐ranking pregnant females attempt to minimize male interest in other females, while reinforcing their own status and potentially delaying conception in others. These findings indicate that female‐mating competition is more important than considered earlier, and may be a factor in the evolution of nonconceptive mating in humans. Am. J. Primatol. 71:1011–1020, 2009. © 2009 Wiley‐Liss, Inc.     

Proximity patterns of female western lowland gorillas (Gorilla gorilla gorilla) during the six months after parturition

Studies of wild mountain gorillas have demonstrated strong preferences among new mothers for the silverback. Protection against infanticide has been theorized to be the primary cause for this attraction. We examined social partner preferences in captive western lowland mothers during the 6 mo after parturition and found that juveniles and females were the primary members of the new mothers' social network. Mothers spent significantly more time in close proximity with both of these subgroups than with the silverback. Proximity patterns changed over time: new mothers spent more time near females in the month after parturition than in the month prior to parturition, and spatial proximity increased again in months 2-6 postparturition. These findings differ from those reported for wild mountain gorillas, which may reflect the lack of infanticide risk in captivity. Given current hypotheses that infanticide may be a limited in western lowland gorillas, the social partner preferences observed here may be indicative of patterns in wild populations.     

Postconflict behavior in captive western lowland gorillas (Gorilla gorilla gorilla)

Postconflict (PC) behaviors, including reconciliation and consolation, have been observed in many primate and several nonprimate species. Using the PC-matched control (MC) method, PC behavior was examined in two groups (n=13) of captive western lowland gorillas, a species for which no conflict resolution data have been published. Analyses of 223 conflicts showed significantly more affiliation between former opponents after a conflict when compared to control periods, indicating reconciliation. Results also showed significantly more affiliation between the victim and a third-party after a conflict, indicating consolation. Both solicited and unsolicited consolation were observed. The majority of the affiliative interactions observed for both reconciliation and consolation were social proximity, which suggests that unlike most nonhuman primates, proximity, rather than physical contact, may be the main mechanism for resolving conflicts in western lowland gorillas. PC behavior was not uniform throughout the groups, but rather varied according to dyad type.     

Home-range use and intergroup encounters in western gorillas (Gorilla g. gorilla) at Lossi forest, North Congo

I present data on home-range use and types of intergroup encounters for one group (Apollo) of western gorillas (Gorilla gorilla gorilla) from a new study site in the Republic of Congo. The total home-range size of the focal group, which I calculated by superimposing a 100 m x 100 m grid over the mapped daily path traveled, was 11 km2. The majority (73%) of the group's home range was used exclusively, although at the periphery it overlapped with the ranges of three other groups. Most encounters (86%) with other groups (n = 14) took place in the periphery of the home range, and appeared to involve access to fruit trees. The focal group silverback's encounters with solitary silverbacks occurred throughout the focal group's home range, did not involve access to fruit, and typically resulted in aggressive or avoidance behavior. The focal group silverback's response to other group males was more varied: it included tolerance (64%), avoidance (14%), and aggression (21%), and was dependent upon the identity of the extragroup male. The focal group exhibited an unusual form of tolerant behavior toward some other groups by occasionally forming "nesting supergroups" (two groups nested together overnight at distances of 30-50 m). The western gorillas at Lossi were somewhat fluid in their grouping. Subgrouping and supergrouping occurred, although more infrequently than reported previously, and with a new twist: subgrouping did not necessarily require a silverback's presence. I stress the need for intraspecific comparisons and more complete data sets on western gorilla social organization.     

Feeding ecology of western lowland gorillas in the Nouabalé-Ndoki National Park,Congo

The feeding ecology of western lowland gorillas (Gorilla gorilla gorilla) living in the Nouabalé-Ndoki National Park, northern Congo, was surveyed for one full year. This is the first record to make clear the seasonal changes in the feeding habits of gorillas in a whole year, living in the primary lowland forest almost completely undisturbed. Fecal contents, feeding traces, and direct observation were analyzed with reference to a fruit availability survey. Although the gorillas fed largely on fruits in the forest, their basic diet was fibrous parts of plants, including shoots, young leaves, and bark. Terrestrial herbaceous vegetation, such as monocotyledons of the Marantaceae and aquatic herbs having much protein content and minerals, were frequently eaten even in the fruiting season. As these highly nutritious fibrous foods were superabundant all year, the major foods of the Ndoki gorillas seemed to be those plants. However, they selected fruits as their alternative food resources in the fruiting season. Gorillas foraged on many fruit species, while showing strong preferences for some particular species. The swamp forest, including marshy grasslands, was an important and regular habitat for the Ndoki gorillas.     

Spatial ecology of jaguars,pumas, and ocelots: a review of the state of knowledge

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