Chimpanzee feeding ecology and fallback food use in the montane forest of Nyungwe National Park,Rwanda

Almost all primates experience seasonal fluctuations in the availability of key food sources. However, the degree to which this fluctuation impacts foraging behavior varies considerably. Eastern chimpanzees (Pan troglodytes schweinfurthii) in Nyungwe National Park, Rwanda, live in a montane forest environment characterized by lower primary productivity and resource diversity than low‐elevation forests. Little is known about chimpanzee feeding ecology in montane forests, and research to date predominantly relies on indirect methods such as fecal analyses. This study is the first to use mostly observational data to examine how seasonal food availability impacts the feeding ecology of montane forest chimpanzees. We examine seasonal changes in chimpanzee diet and fallback foods (FBFs) using instantaneous scan samples and fecal analyses, supported by inspection of feeding remains. Chimpanzee fruit abundance peaked during the major dry season, with a consequent change in chimpanzee diet reflecting the abundance and diversity of key fruit species. Terrestrial herbaceous vegetation was consumed throughout the year and is defined as a “filler” FBF. In contrast to studies conducted in lower‐elevation chimpanzee sites, figs (especially Ficus lutea) were preferred resources, flowers were consumed at seasonally high rates and the proportion of non‐fig fruits in the diet were relatively low in the current study. These divergences likely result from the comparatively low environmental diversity and productivity in higher‐elevation environments.     

Fallback foods and dietary partitioning among Pan and gorilla

Recent findings on the strong preference of gorillas for fruits and the large dietary overlap between sympatric gorillas and chimpanzees has led to a debate over the folivorous/frugivorous dichotomy and resource partitioning. To add insight to these arguments, we analyze the diets of sympatric gorillas and chimpanzees inhabiting the montane forest of Kahuzi-Biega National Park (DRC) using a new definition of fallback foods (Marshall and Wrangham: Int J Primatol 28 [2007] 1219–1235). We determined the preferred fruits of Kahuzi chimpanzees and gorillas from direct feeding observations and fecal analyses conducted over an 8-year period. Although there was extensive overlap in the preferred fruits of these two species, gorillas tended to consume fewer fruits with prolonged availability while chimpanzees consumed fruits with large seasonal fluctuations. Fig fruit was defined as a preferred food of chimpanzees, although it may also play a role as the staple fallback food. Animal foods, such as honey bees and ants, appear to constitute filler fallback foods of chimpanzees. Tool use allows chimpanzees to obtain such high-quality fallback foods during periods of fruit scarcity. Among filler fallback foods, terrestrial herbs may enable chimpanzees to live in small home ranges in the montane forest, whereas the availability of animal foods may permit them to expand their home range in arid areas. Staple fallback foods including barks enable gorillas to form cohesive groups with similar home range across habitats irrespective of fruit abundance. These differences in fallback strategies seem to have shaped different social features between sympatric gorillas and chimpanzees. Am J Phys Anthropol 140:739–750, 2009. © 2009 Wiley-Liss, Inc.     

The Influence of Seasonal Variation on Chimpanzee (Pan troglodytes schweinfurthii) Fallback Food Consumption, Nest Group Size, and Habitat Use in Gishwati, a Montane Rain Forest Fragment in Rwanda

The increased number of primates living in fragmented habitats necessitates greater knowledge of how they cope with large-scale changes to their environment. Chimpanzees (Pan troglodytes) are exceptionally vulnerable to forest fragmentation; however, little is known about chimpanzee feeding ecology in fragments. Although chimpanzees have been shown to prefer fruit when it is available and fall back on more abundant lower quality foods during periods of fruit scarcity, our understanding of how chimpanzees use fallback foods in forest fragments is poor. We examined how chimpanzees cope with periods of fruit scarcity in Gishwati Forest Reserve, a disturbed montane rain forest fragment in Rwanda. We assessed seasonal changes in chimpanzee diet and the use of preferred and fallback foods through fecal and food site analysis. We also examined seasonal variation in nest group size and habitat use through marked nest censuses. We found that chimpanzees experienced a seasonal reduction in preferred fruit availability, which led to a seasonal diet shift to more fibrous foods, including several that functioned as fallback foods. Our results suggest that during periods of fruit scarcity the chimpanzees also reduced nest group size. However, we found that the chimpanzees did not alter their habitat use between high- and low-fruit seasons, which suggests that the small size of the forest limits their ability to change their seasonal habitat use. Consequently, fallback foods appear to be particularly important in small food-impoverished habitats with limited ranging options.     

Influence of Food Resources on the Ranging Pattern of Northern Pig-tailed Macaques (Macaca leonina)

Food availability may influence primates’ home range size and use. Understanding this relationship may facilitate the design of conservation strategies. We aimed to determine how fruit availability influences the ranging patterns of a group of northern pig-tailed macaques (Macaca leonina) living around the visitor center of Khao Yai National Park, Thailand. We predicted that macaques would increase their range during low fruit abundance periods to gather high-quality food and that they would go where there are more fruits or more fruits of particular species. We also predicted that human food, linked to human presence, would attract the macaques. We followed the macaques and recorded their diet and movements within their home range. We superimposed a grid on kernels defining the monthly home range surface to compare spatially macaques’ travel and the availability of fruits measured on botanical transects. Our results showed that the macaques increased their monthly home range in March, probably to obtain newly available fruits. During high fruit abundance seasons, they spent more time near particular fruit species. In August and September, although fruits became rare again, macaques kept their home range large, perhaps to find enough fruits as supplies dwindled. Finally, from October to February, they decreased their monthly home range size while consuming human food, a high-quality item. In conclusion, the macaques used several ranging strategies according to fruit availability. However, we think that, without human food, macaques would tend to increase their range during low fruit abundance periods, as predicted.     

Ecological correlates of space use patterns in wild western lowland gorillas

The distribution of resources is a crucial determinant of animals' space use (e.g., daily travel distance, monthly home range size, and revisitation patterns). We examined how variation in ecological parameters affected variability in space use patterns of western lowland gorillas, Gorilla gorilla gorilla. They are an interesting species for investigating this topic because key components of their diet are nonfruit items (herbaceous vegetation and tree leaves) that occur at low density and are sparsely distributed, and fruits, which show high spatiotemporal variation in availability. We estimated how availability of nonfruit foods and fruit, frugivory (proportion of feeding time consuming fruit), and swamps in areas used by the gorillas influenced daily travel distance, monthly home range size, and revisit frequency to grid cells in the home range of one habituated gorilla group in Loango National Park, Gabon. Using location data from 2015 to 2018, we found that the gorillas decreased their daily travel distance as both the density of nonfruit foods and the proportion of swamps in areas used increased. Daily travel distances were shorter when both frugivory and availability of fruit were higher, yet, daily travel distances were longer when availability of fruit was low but frugivory was still high. Furthermore, monthly home range size increased as frugivory increased and monthly revisit frequencies to an area increased as fruit availability of an area increased. In conclusion, the availability of both nonfruit and fruit influenced the gorillas' space use patterns. Gorillas decreased foraging effort when food availability was high but were willing to incur increasing foraging costs to feed on fruit when availability was low. This study highlights how animals have to adjust their space use with changing resource availability and it emphasizes the value of examining multiple parameters of space use.     

Daily Energy Balance and Protein Gain Among <Emphasis Type="Italic">Pan troglodytes verus</Emphasis> in the Taï National Park,Côte d’Ivoire

Energy balance and protein gain contribute significantly to an animal’s survival. Although data are available for certain species in captive settings, there is little information on these factors for primates living in their natural environments. In this preliminary study, we combined detailed behavioral, phonological, and chemical data for a well habituated chimpanzee community from the Taï National Park, Côte d’Ivoire, with estimates of energy gain and expenditure from captive chimpanzees and humans to investigate how energy balance and protein gain across age-sex categories are affected by seasonal variations in food availability and how chimpanzees correspondingly alter their feeding and daily journey length (DJL). Comparisons between fruiting seasons characterized by varying quantities and qualities of available food revealed that food quality had the largest effect on individual energy balance and protein gain. Within given fruit seasons, energy balance and protein gain did not vary among age-sex categories. However, there was, variation across seasons among adult males and young of both sexes, but not among adult females. Our study revealed important effects of periods of food scarcity to which chimpanzees reacted by reducing their DJL and increasing their feeding time.     

Diet composition of chimpanzees inhabiting the montane forest of Kahuzi,Democratic Republic of Congo

The diet of chimpanzees was investigated by direct observations, feeding remains, and fecal analysis from January 1994 to December 2000 in the montane forest of Kahuzi-Biega National Park. A total of 171 food items were identified, among which 156 items were plant materials belonging to 114 species from 57 taxonomic families. Chimpanzees consumed 66 species of fruits (62 species of pulps and four species of seeds). Results of fecal analysis showed that fig fruits were the most frequently eaten. Their seeds occurred in 92% of a total of 7212 chimpanzee fecal samples. The chimpanzees changed their diet according to seasonal and annual variations in both abundance and diversity of fruit species. However, they are very selective frugivores. Only a few pulp-fruit species are regularly identified in their fecal samples. During the rainy season, when ripe fruit was scarce, chimpanzees relied heavily on piths and leaves. They swallowed leaves of two species of Commelinaceae without chewing, probably for medical purposes. Animal foods were eaten infrequently. The montane forest of Kahuzi, where chimpanzees range up to 2600 m above sea level, may be the highest altitudinal limit ever recorded for their distribution. Compared to other chimpanzee habitats, Kahuzi has a low diversity of fruit species and the availability of a few pulp-fruit species may be critical to the survival of Kahuzi chimpanzees.     

Ranging Patterns of Chimpanzees in a Montane Forest of Kahuzi,Democratic Republic of Congo

I studied ranging patterns of a semihabituated unit-group of chimpanzees for 60 mo at Kahuzi. They had a total home range of 12.81 km² and a mean annual home range of 7.55 km². Considering the low density of chimpanzees in the area vis-à-vis chimpanzees in arid areas, their home range is very small. Kahuzi chimpanzees used the home range in a clumped pattern, frequently visiting the core area and only rarely entering peripheral areas. The monthly range changes with fruit availability, increasing during periods of fruit scarcity. There was no consistent seasonal difference in the size of the home range. However, use of different habitat types may vary seasonally. While there was no seasonal effect in the use of primary forest, the chimpanzees showed a statistically consistent seasonal difference in their use of secondary forest, visiting it mainly during the dry season when fig trees were in fruit. Since the primary forest provides them with more food fruits, chimpanzees tended to use more frequently the small patches of primary forest in their home range. Thus, the size and distribution of small fragmented primary forests may be an important factor influencing the ranging pattern of chimpanzees at Kahuzi.     

Chimpanzee seed dispersal quantity in a tropical montane forest of Rwanda

We describe chimpanzee seed dispersal in the tropical montane forest of Nyungwe National Park (NNP), Rwanda, for a total of three years from January 1998 through May 2000 and May 2006 through March 2007. Relatively few studies have examined chimpanzee seed dispersal in montane communities where there are generally fewer fruiting tree species than in lowland forests. Such studies may reveal new insights into chimpanzee seed dispersal behaviors and the role that they play in forest regeneration processes. Chimpanzees are large‐bodied, highly frugivorous, and tend to deposit the seeds of both large‐ and small‐seeded fruits they consume in a viable state. We found that chimpanzees dispersed a total of 37 fruiting species (20 families) in their feces, 35% of which were large‐seeded trees (≥0.5 cm). A single large‐seeded tree, Syzygium guineense, was the only species to be dispersed in both wadges and feces. Based on phenological patterns of the top five large‐seeded tree species found in chimpanzee feces, our results indicate that chimpanzees do not choose fruits based on their availability. There was, however, a positive relationship between the presence of Ekebergia capensis seeds in chimpanzee feces and S. guineense seeds in chimpanzee wadges and their respective fruit availabilities. Our data reveal that proportionately fewer chimpanzee fecal samples at NNP contained seeds than that reported in two other communities in the Albertine Rift including one at mid‐elevation and one in montane forest. As in other chimpanzee communities, seeds of Ficus spp. were the most common genus in NNP chimpanzee feces. Our data do not support previous studies that describe Ficus spp. as a fallback food for chimpanzees and highlights an intriguing relationship between chimpanzees and the large‐seeded tree species, S. guineense. Am. J. Primatol. 71:901–911, 2009. © 2009 Wiley‐Liss, Inc.     

Diet and seasonal changes in sympatric gorillas and chimpanzees at Kahuzi–Biega National Park

Based on 8 years of observations of a group of western lowland gorillas (Gorilla beringei graueri) and a unit-group of chimpanzees (Pan troglodytes schweinfurthii) living sympatrically in the montane forest at Kahuzi–Biega National Park, we compared their diet and analyzed dietary overlap between them in relation to fruit phenology. Data on fruit consumption were collected mainly from fecal samples, and phenology of preferred ape fruits was estimated by monitoring. Totals of 231 plant foods (116 species) and 137 plant foods (104 species) were recorded for gorillas and chimpanzees, respectively. Among these, 38% of gorilla foods and 64% of chimpanzee foods were eaten by both apes. Fruits accounted for the largest overlap between them (77% for gorillas and 59% for chimpanzees). Gorillas consumed more species of vegetative foods (especially bark) exclusively whereas chimpanzees consumed more species of fruits and animal foods exclusively. Although the number of fruit species available in the montane forest of Kahuzi is much lower than that in lowland forest, the number of fruit species per chimpanzee fecal sample (average 2.7 species) was similar to that for chimpanzees in the lowland habitats. By contrast, the number of fruit species per gorilla fecal sample (average 0.8 species) was much lower than that for gorillas in the lowland habitats. Fruit consumption by both apes tended to increase during the dry season when ripe fruits were more abundant in their habitat. However, the number of fruit species consumed by chimpanzees did not change according to ripe fruit abundance. The species differences in fruit consumption may be attributed to the wide ranging of gorillas and repeated usage of a small range by chimpanzees and/or to avoidance of inter-specific contact by chimpanzees. The different staple foods (leaves and bark for gorillas and fig fruits for chimpanzees) characterize the dietary divergence between them in the montane forest of Kahuzi, where fruit is usually scarce. Gorillas rarely fed on insects, but chimpanzees occasionally fed on bees with honey, which possibly compensate for fruit scarcity. A comparison of dietary overlap between gorillas and chimpanzees across habitats suggests that sympatry may not influence dietary overlap in fruit consumed but may stimulate behavioral divergence to reduce feeding competition between them.     

Ranging behavior of eastern hoolock gibbon (Hoolock leuconedys) in a northern montane forest in Gaoligongshan,Yunnan, China

Generally, food abundance and distribution exert important influence on primate ranging behavior. Hoolock gibbons (genus Hoolock) live in lowland and montane forests in India, Bangladesh, Myanmar and China. All information about hoolock gibbons comes from studies on western hoolock gibbons (Hoolock hoolock) living in lowland forest. Between August 2010 and September 2011, we studied the ranging behavior of one habituated group of eastern hoolock gibbon (H. leuconedys) living in a seasonal montane forest in Gaoligongshan, Yunnan, China. Results show that the study group did not increase foraging effort, calculated in this study as the daily path length, when fruit was less available. Instead, the gibbons fed more on leaves and decreased traveling to conserve energy. They relied heavily on a single food species in most study months which was patchily distributed within their total (14-month) home range, and during most months they used only a small portion of their total home range. In order to find enough food, the group shifted its monthly home range according to the seasonal availability of food species. To satisfy their annual food requirements, they occupied a total home range of 93 ha. The absence of neighboring groups of gibbons and the presence of tsaoko cardamom (Amomum tsaoko) plantations may also have influenced the ranging behavior of the group. Further long-term studies of neighboring groups living in intact forests are required to assess these effects.     

The Influence of Temporal Changes in Fruit Availability on Diet Composition and Seed Handling in Blue Monkeys (Cercopithecus mitis doggetti)1

We investigated the relation between temporally varying resources, diet composition, and seed-handling behaviors in a group of blue monkeys (Cercopithecus mitis doggetti) in a tropical montane forest of Rwanda. Changes in diet composition were related to concurrent phenological studies of fruit-producing trees, and density and abundance of tree resources within the monkey's home range. Fruit composed nearly 50 percent of the diet. Over 50 percent of the fruits eaten had juicy fleshy pulp. Observations of seed handling behavior provided insights into the role of these animals as potential seed dispersal agents. The monkeys moved the seeds of 29 species out of parent canopies by defecating seeds intact and by potentially carrying seeds in cheek pouches and dropping them later. Seeds of 18 species were found intact in fecal piles. Our study showed community-level phenology patterns did not indicate a decrease in fruit availability during the study period, but an analysis of the preferred fruits consumed by the monkeys showed distinct periods of low fruit availability. The study period included two dry seasons; only one of these produced a period of fruit scarcity for the animals. The animals employed different strategies during times of preferred fruit scarcity. They increased consumption of leaves and other fleshy fruits, and diet diversity increased, or became mainly seed predators and diet diversity decreased. The variable responses of these monkeys to changes in food availability highlights their dietary plasticity and imposes significant variations in their role as potential seed dispersers.     

Foraging strategies of black-fronted titi monkeys (<Emphasis Type="Italic">Callicebus nigrifrons</Emphasis>) in relation to food availability in a seasonal tropical forest

Many primates have to cope with a temporal scarcity in food availability that shapes their foraging strategies. Here we investigated the changes in diet, activity, and ranging behavior of a group of black-fronted titi monkeys (Callicebus nigrifrons) according to the availability of the main high-nutritional-density item in their diet and the foraging strategy adopted when this food is scarce. We monitored one habituated group using instantaneous scan sampling over 1 year (533 h of observation, 61 days) in a seasonal tropical forest fragment (245 ha). We simultaneously collected data on food availability with fruit traps. The titi monkeys consumed fleshy fruits, the main high-nutritional-density item of their diet, in accordance with its availability, and the availability of this item modulated the ingestion of vegetative plant parts, a relatively low-nutritional-density food. During high fleshy fruit availability, the titi monkeys consumed more fleshy fruits, flowers, and invertebrates. They also traveled more, but concentrated their activity in a central area of their home range. Conversely, during fleshy fruit scarcity, they increased the breadth of their diet, switching to one richer in seeds and vegetative plant parts, and with greater plant diversity. At the same time, they reduced most energy-demanding activities, traveling less and over shorter distances, but using their home range more broadly. Corroborating the optimal foraging theory, titi monkeys altered foraging strategies according to temporal food fluctuations and responded to low fleshy fruit availability by changing their diet, activity, and ranging behavior. The adoption of a low-cost/low-yield strategy allowed us to classify them as energy minimizers.     

Phenology of figs in Budongo Forest Uganda and its importance for the chimpanzee diet

This paper reports on the phenological patterns of figs in Budongo Forest, Uganda, and how it relates to chimpanzee food availability in different seasons. In addition, we analysed the dung of chimpanzees to understand the composition of fruits in their diet. The aim of our study was to assess Ficus phenology and how it affects chimpanzee diet. Fifteen species of figs were monitored for fruit (syconium) and leaf phenology between June 2000 and 2001. Ficus fruit production varied significantly between and within species, and also with tree trunk and crown diameters. Fig fruit production was asynchronous and individual fig trees produced crops from one to five times in a year. In addition to fruits, chimpanzees fed on young leaves of some Ficus species. Shedding of old Ficus leaves coincided with the dry season, followed by appearance of young leaves. The dry season in Budongo is a period of general fruit scarcity. The combination of fig fruits and young leaves make up the most important food in the diet of chimpanzees. From the chimpanzee dung, more than 78% of seeds comprised fig ‘seeds’ (nutlets) and the rest of the diaspores were from other tree species. Our findings suggest that chimpanzees disperse large number of diaspores in their dung, thereby serving as important agents of natural forest regeneration.     

Dietary Response of Chimpanzees and Cercopithecines to Seasonal Variation in Fruit Abundance. I. Antifeedants

In order to understand dietary differentiation among frugivorous primates with simple stomachs, we present the first comparison of plant diets between chimpanzees and cercopithecine monkeys that controls for food abundance. Our aim was to test the hypothesis that monkeys have a more diverse diet as a result of their dietary tolerance for chemical antifeedants. Our study species are chimpanzees, blue monkeys, redtail monkeys, and gray-cheeked mangabeys living in overlapping ranges in Kibale National Park, Uganda. We indexed food abundance by the percentage of trees having ripe fruit within the range of each group; it varied widely during the year. Chimpanzees spent almost 3 times as much of their feeding time eating ripe fruits as the monkeys did and confined their diets almost exclusively to ripe fruits when they were abundant. Monkeys maintained a diverse diet at all times. When ripe fruit was scarce chimpanzee and monkey diets diverged. Chimpanzees relied on piths as their main fallback food, whereas monkeys turned to unripe fruits and seeds. For each primate group we calculated the total weighted mean intake of 5 antifeedants; condensed tannins (CT), total tannins assayed by radial diffusion (RD), monoterpenoids (MT), triterpenoids (TT), and neutral-detergent fiber (NDF). Monkeys had absolutely higher intakes of CT, RD, MT, and TT than those of chimpanzees, and their intake of NDF did not differ from that of chimpanzees, appearing relatively high given their lower body weights. However contrary to expectation, dietary divergence during fruit scarcity was not associated with any change in absolute or relative intake of antifeedants. For example, fruit scarcity did not affect the relative intake of antifeedants by cercopithecines compared to chimpanzees. Our results establish chimpanzees as ripe-fruit specialists, whereas cercopithecines are generalists with a higher intake of antifeedants. The low representation of ripe fruits in the diets of cercopithecines has not been explained. An important next step is to test the hypothesis that the difference between Kibale chimpanzees and cercopithecines represents a more general difference between apes and monkeys.     

Ranging of <Emphasis Type="Italic">Rhinopithecus bieti</Emphasis> in the Samage Forest,China. II. Use of Land Cover Types and Altitudes

We investigated composition and structure of a temperate montane forest called Samage at Baimaxueshan National Nature Reserve in Yunnan, one of the last refuges for the highly endangered black-and-white snub-nosed monkeys (Rhinopithecus bieti). There is a patchwork of vegetation types at Samage, and we distinguished 6 major land cover types within the home range of the focal group. We tracked the semihabituated Gehuaqing band for a full annual cycle to study their habitat utilization and altitudinal ranging. We analyzed the group’s selective use of particular habitat types via selection ratios. We calculated habitat availability from a GIS database. We found that they used mixed deciduous broadleaf/conifer forest disproportionately to its availability in all months. Subjects completely avoided meadows. Pine and evergreen broadleaf forests acted as corridors between patches of mixed forest and monkeys visited them occasionally, but at low frequencies and mostly in transit. The focal band stayed at elevations ranging from ca. 2600 m to 4000 m, and the mean elevation used is 3200 m. We found evidence for seasonal variation in use of elevational zones. The band stayed at significantly higher elevations in summer than in spring. The descent in spring was likely related to a flush of immature leaves at low-lying elevations. Availability of preferred fruits also had a highly positive influence on altitudinal ranging, i.e., during months with high fruit availability (late summer, early fall), the band stayed at medium elevations where preferred fruits were most abundant. Higher concentrations of lichens and the snub-nosed monkeys’ search for not yet depleted fruits probably caused them to remain at mid-elevations in winter. There is no significant correlation between climate parameters and elevation used. One of the main inferences of this investigation is that, contrary to previous accounts, Rhinopithecus bieti is not universally associated with high-elevation dark fir forest, but at Samage exhibits an overwhelming preference for mixed forest. Moreover, our analyses support the hypothesis that elevational migration, in this temperate-subtropical forest, is influenced by the temporal fruiting of major food trees and that climate has only a negligible effect on elevation use. Dayong Li and Cyril C. Grueter contributed equally to the paper.     

Seasonal variation of diet and time budget of Eastern hoolock gibbons (Hoolock leuconedys) living in a northern montane forest

Most gibbons dwell in the tropical forests of Southeastern Asia, but eastern hoolock gibbons (Hoolock leuconedys) survive in high montane forest ranging from 1,600 to 2,700 m a.s.l. in Gaoligongshan (>24°30′N), Yunnan, China. To assess the behavioral adaptations of hoolock gibbons to the montane forest, we related temperature and food availability within the habitat to the seasonal behavioral patterns of a family group and a solitary female between August 2010 and September 2011 in Nankang, Gaoligongshan National Nature Reserve. The maximum temperature was 29.2 °C and the minimum temperature was ?0.3 °C during the period. The monthly mean temperature was <10 °C between December and February, making Nankang the coldest gibbon habitat reported so far. Nonfig fruit and fig availability declined to nearly zero in cold months. The family group increased resting and decreased travel and social behaviors when the monthly mean temperature was low. Compared with other gibbon populations, the hoolock gibbons spent proportionally less time feeding on figs and other fruit than other gibbon populations except Nomascus concolor and Symphalangus syndactylus. Only 36 species of plants provided nonfig fruit or figs, which is less than the number of fruit species consumed by any other gibbon population observed during a similar period of time (about 1 year). Hoolock gibbons shifted their diet to leaves and increased feeding time when fruit was not available. We conclude that diet flexibility and an energy-conserving strategy during the cold season when fruit is scarce have enabled the hoolock gibbons to survive in a northern montane forest.     

Fragmented living: Behavioural ecology of primates in a forest fragment in the Lopé Reserve, Gabon

A 17-month study was made of the primates using a 9-ha “island” of forest, surrounded by savanna, in the northern part of the Lopé Reserve, Gabon. One group ofCercopithecus cephus (plus a young maleCercopithecus nictitans who was in permanent association with them) were resident in the fragment and groups of five other species of primates made visits during 127 days of observation:Pan troglodytes, 15 visits;Cercocebus albigena, 10;Colobus satanas, 3;Cercopithecus nictitans, 2;C. pogonias, 1. Visits were also made by lone males of three species,C. nictitans, Cercocebus albigena, andMandrillus sphinx. The eighth species of diurnal primate present at Lopé,Gorilla g. gorilla, did not visit the fragment during the study. Compared to conspecific groups in neighbouring continuous forest, primates in the fragment ate less fruit, seeds and flowers and more insects and leaves. The local population density of primates resident in the fragment was equivalent to that of the neighbouring continuous forest where all eight species occur, despite the diversity and abundance of fruit being less in the fragment. The costs imposed on the resident group by the reduced diversity and availability of preferred fruit foods appeared to be offset by a number of benefits that increased individual feeding efficiency for monkeys residing within a single fragment. These included lower travel costs, reduced feeding competition between individuals through group fission, and excellent knowledge of the location and quality of food resources in the small home range. It is also possible that the overall negative impact of inter-specific feeding competition was lower in fragments than in continuous forest and that micro-habitat differences resulted in an increased availability of palatable insect and leaf fallback foods in the fragment.     

Home ranges in adult Scandinavian brown bears (Ursus arctos): effect of mass, sex, reproductive category, population density and habitat type

Annual home-range size indices for 36 male and 52 female adult brown bears Ursus arctos in two study areas in central and northern Scandinavia were estimated to evaluate factors believed to influence home-range size. Male home ranges were larger than home ranges of lone females after controlling for the sexual size dimorphism acting on metabolic needs. Further, home ranges of females with cubs were smaller than home ranges of lone females and females with yearlings. Thus, differences in metabolic need were not able to explain the variation in range size among females of different reproductive categories or between males and females, suggesting roaming behaviour of males in this promiscuous species. Home-range size in both males and females was inversely related to population density along a density gradient that was not linked to food availability. This contradicts the hypothesis that females use the minimum areas that sustain their energy requirements. However, on a large geographical scale a negative relationship between range size and food availability was evident. The annual home ranges in inland boreal environments in Scandinavia are the largest reported for brown bears in Eurasia, and similar to those in inland boreal and montane environments in North America.     

Fruit availability, chimpanzee diet, and grouping patterns on Rubondo Island, Tanzania

We examined seasonal patterns of fruit availability, dietary quality, and group size in the descendants of an introduced chimpanzee population on Rubondo Island, Tanzania. The site has supported a free-ranging population without provisioning for 40 years. Our goals were to determine whether Rubondo chimpanzees experience periods of fruit shortage, and whether they respond to changes in fruit availability similarly to chimpanzees at endemic sites. We indexed the fruit availability of tree and liana species on transects stratified across three chimpanzee ranging areas. We used fecal analyses to evaluate seasonal changes in diet, and used data on party size and nesting group size to examine seasonal patterns of grouping. Tree fruit availability was positively correlated with rainfall, with a period of relative tree fruit scarcity corresponding with the long dry season. Liana fruit availability was not related to rainfall, and lianas exhibited less variable fruiting patterns across seasons. Fruits made up the majority of the chimpanzee diet, with lianas accounting for 35% of dietary fruit species. Fruits of the liana Saba comorensis were available during all months of phenological monitoring, but they were consumed more when tree fruit was scarce, suggesting that Saba comorensis fruits may be a fallback food for Rubondo chimpanzees. There were no increases in consumption of lower-quality plant parts between seasons, and there were no changes in group size between seasons. These results contrast with evidence from several endemic chimpanzee study sites, and indicate that Rubondo chimpanzees may have access to abundant and high-quality foods year round.