Use of space in a non-naturalistic environment by chimpanzees (Pan troglodytes) and lowland gorillas (Gorilla gorilla gorilla)

Chimpanzees and gorillas are the two most common species of great ape in captive facilities in North America. This study examined patterns of space use by 14 gorillas and six chimpanzees housed in similar non-naturalistic environments at Lincoln Park Zoo in Chicago, IL. The location of each individual was recorded in relation to elements of the environment over a two-year period. These data were compared to volumetric measurements of the enclosures to determine “preferences” for particular environmental elements. Chimpanzees preferred the highest tier of the enclosure and the gorillas preferred the floor level. Both species showed preferences for doorways, corners and the mesh barriers adjacent to keeper areas. These data supplement data from wild populations of apes and provide information useful for those seeking to design new ape enclosures or renovate existing facilities.     

Transfer and Acclimatization Effects on the Behavior of Two Species of African Great Ape (<Emphasis Type="BoldItalic">Pan troglodytes</Emphasis> and <Emphasis Type="BoldItalic">Gorilla gorilla gorilla</Emphasis>) Moved to a Novel and Naturalistic Zoo Environment

Studying the effects of moving animals to new enclosures is of value to both captive managers and to scientists interested in the complex interplay between environment and behavior. Great apes represent some of the greatest challenges in this regard. Given the cognitive sophistication of these species and the substantial investments in new primate facilities, these investigations are particularly important. Using post-occupancy evaluation (POE) methodology, we compared behavior exhibited by chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla gorilla) in indoor hardscape-type exhibits to behavior of the same individuals in new naturalistic enclosures with outdoor access. In the new facility, chimpanzees showed decreases in the frequency of abnormal behaviors and visual monitoring of humans (attention behaviors) whereas gorillas exhibited reduced agonism as well as decreased attention behaviors. Both gorillas and chimpanzees demonstrated higher rates of inactivity after transfer to the new facility. All subjects in addition demonstrated transitory changes in behavior after the move to the new facility (higher rates of scratching in yr 1 than in subsequent years), indicating a period of acclimatization. Seasonal effects on feeding behavior and activity levels (both species were more active in the winter) were evident as well. The results indicate that behavioral adjustment to a new facility is an extended process for both species and that seasonal effects should be considered in longitudinal analyses of acclimatization. Behavioral patterns supported the benefits of naturalistic, functional exhibit spaces and the utility of post-occupancy evaluations in assessing captive animal welfare.     

Preference for structural environmental features in captive lowland gorillas (Gorilla gorilla gorilla)

Increased interest in the behavioral effects of captive environments and advances in zoo design have resulted in a proliferation of “naturalistic” animal habitats. Although scientists have demonstrated that such exhibits have some positive effects on behavior, very little is known about the complex relationships between these specialized environments and behavior. This study sought to determine preferences for structural environmental features, such as slope and trees, exhibited by captive lowland gorillas (Gorilla gorilla gorilla). An average of 496 location scans were collected on each of 23 gorillas, housed in 6 groups. The results indicate that enclosure usage was significantly associated with the features of slope, nearness to holding facility, and presence of environmental components additional to substrate (e.g., tree or rock). In particular, areas with flat ground that were near the holding building and that included at least one component additional to substrate were preferred by all animals. © 1993 Wiley-Liss, Inc.     

Food Preferences Among Captive Western Gorillas (Gorilla gorilla gorilla) and Chimpanzees (Pan troglodytes)

I used a zoological park setting to address food preferences among gorillas (Gorilla gorilla gorill) and chimpanzees (Pan troglodytes). Gorillas and chimpanzees are different sizes, and consequently, have been traditionally viewed as ecologically distinct. Sympatric western gorillas and chimpanzees have proved difficult to study in the wild. Limited field data have provided conflicting information about whether gorillas are fundamentally different from chimpanzees in diet and behavior. Fruit eating shapes the behavior of most apes, but it is unclear whether the large-bodied gorillas are an exception to this rule, specifically whether they are less selective and more opportunistic fruit eaters than chimpanzees are. My research provides experimental observational data to complement field data and to better characterize the diets and food preferences of the African apes. During laboratory research at the San Francisco Zoological Gardens, I examined individual and specific differences in food preferences of captive gorillas and chimpanzees via experimental paired-choice food trials with foods that varied in nutritional content. During the study, I offered 2500 paired-food choices to 6 individual gorillas and 2000 additional pairs to them as a group. I also proffered 600 food pairs to 4 individual chimpanzees. Despite expectations of the implications of body size differences for diet, gorillas and chimpanzees exhibited similar food preferences. Both species preferred foods high in non-starch sugars and sugar-to-fiber ratios, and low in total dietary fiber. Neither species avoided foods containing tannins. These data support other suggestions of African apes sharing a frugivorous adaptation.     

Utilization of space by adult and juvenile groups of captive chimpanzees (Pan troglodytes)

A systematic analysis of space utilization in the home enclosures of four adult and three juvenile social groups of chimpanzees (Pan troglodytes) was conducted at the Primate Foundation of Arizona. The locations of all members of each group (excluding nursing infants) were recorded several times per week over a 3-month period. Adult chimpanzees were observed significantly more often in small vs large cages, on upper vs lower levels, and near cage perimeters vs cage centers. Analyses of sex differences in adults revealed that adult females are largely responsible for these space use patterns; adult males show only a significantly higher usage of perimeter areas. Individual differences were found in the habitual use of certain enclosure sites. Juveniles show no spatial patterns with regard to the above parameters but appear to evenly use all available space. Both adults and juveniles were observed to be in contact with mesh barriers more often than with solid walls. These findings suggest important elements that should be incorporated into the caging design of captive chimpanzee facilities.     

Hunting and Occasional Consumption of Prey Items by Chimpanzees at the Primate Foundation of Arizona

Researchers have documented hunting by wild chimpanzees (Pan troglodytes) for >30 yr. However, no one had reported the behavior in captive chimpanzees. The Primate Foundation of Arizona (PFA) is a biomedical research facility, and though every effort is made to ensure that rodents and other indigenous animals do not enter cages, an occasional small mammal or bird enters the outside cage area. We document 18 known successful hunts over 2.5 yr by ≥8 captive chimpanzees housed at PFA. The most common prey were rock squirrels (Cittallus variegatus; n = 8) and birds (n = 7). The most common killing method was a bite to the head (n = 9), indicating that the deaths were deliberate and not accidental. Two adult males, 1 wild- and 1 captive-born, together accounted for 11 of the 18 hunting episodes. The chimpanzees generally captured and killed the prey in their outdoor enclosures. The results have implications for the surveillance of outdoor areas in other facilities and the potential for disease or introduction of parasitic vectors, and are also an interesting comparison to wild chimpanzee behavior.     

Space Use as an Indicator of Enclosure Appropriateness in African Wild Dogs (Lycaon pictus)

A clear understanding of space use is required to more fully understand biological requirements of nonhuman animals in zoos, aid the design of exhibits, and maximize the animals' welfare. This study used electivity indexes to assess space use of two packs of African wild dogs (Lycaon pictus) and the appropriateness of two naturalistic, outdoor enclosures at the San Diego Zoo and Bronx Zoo. The results identified enclosure features that were both underutilized and overutilized. They suggest that replacing underutilized areas with features similar to areas that were overutilized may provide more preferred opportunities for the animals. Assessing space use of animals in human care may serve as an indicator of enclosure appropriateness and could have welfare implications. By looking at the possible reasons for area preferences, animal managers can get an idea of where improvements could be made. Designing future exhibits accordingly thus can provide possible welfare benefits for the animals concerned.     

Genetic diversity of North American captive‐born gorillas (Gorilla gorilla gorilla)

Western lowland gorillas (Gorilla gorilla gorilla) are designated as critically endangered and wild populations are dramatically declining as a result of habitat destruction, fragmentation, diseases (e.g., Ebola) and the illegal bushmeat trade. As wild populations continue to decline, the genetic management of the North American captive western lowland gorilla population will be an important component of the long‐term conservation of the species. We genotyped 26 individuals from the North American captive gorilla collection at 11 autosomal microsatellite loci in order to compare levels of genetic diversity to wild populations, investigate genetic signatures of a population bottleneck and identify the genetic structure of the captive‐born population. Captive gorillas had significantly higher levels of allelic diversity (t₇ = 4.49, P = 0.002) and heterozygosity (t₇ = 4.15, P = 0.004) than comparative wild populations, yet the population has lost significant allelic diversity while in captivity when compared to founders (t₇ = 2.44, P = 0.04). Analyses suggested no genetic evidence for a population bottleneck of the captive population. Genetic structure results supported the management of North American captive gorillas as a single population. Our results highlight the utility of genetic management approaches for endangered nonhuman primate species.     

Skewed birth sex ratio and premature mortality in elephants

Sex allocation theories predict equal offspring number of both sexes unless differential investment is required or some competition exists. Left undisturbed, elephants reproduce well and in approximately even numbers in the wild. We report an excess of males are born and substantial juvenile mortality occurs, perinatally, in captivity. Studbook data on captive births (CB, n = 487) and premature deaths (PD, <5 years of age; n = 164) in Asian and African elephants in Europe and North America were compared with data on Myanmar timber (Asian) elephants (CB, n = 3070; PD, n = 738). Growth in CB was found in three of the captive populations. A significant excess of male births occurred in European Asian elephants (ratio: 0.61, P = 0.044) and in births following artificial insemination (0.83, P = 0.003), and a numerical inclination in North American African elephants (0.6). While juvenile mortality in European African and Myanmar populations was 21–23%, it was almost double (40–45%) in all other captive populations. In zoo populations, 68–91% of PD were within 1 month of birth with stillbirth and infanticide being major causes. In Myanmar, 62% of juvenile deaths were at >6 months with maternal insufficient milk production, natural hazards and accidents being the main causes. European Asian and Myanmar elephants PD was biased towards males (0.71, P = 0.024 and 0.56, P < 0.001, respectively). The skewed birth sex ratio and high juvenile mortality hinder efforts to help captive populations become self-sustaining. Efforts should be invested to identify the mechanism behind these trends and seek solutions for them.     

Skeletal evidence of trauma in African apes, with special reference to the gombe chimpanzees

Incidence of cranial and postcranial skeletal trauma was investigated in samples of chimpanzees (Pan troglodytes troglodytes, P. troglodytes schweinfurthii), lowland gorillas (Gorilla gorilla gorilla), and bonobos (P. paniscus). The larger (adult) samples of chimpanzees (N=127 crania, 92 postcrania) and gorillas (N=136 crania, 62 postcrania) are curated at the Powell-Cotton Museum, Birchington, U.K. The bonobo collection (N=71 crania, 15 postcrania) is housed the Musée Royal de l'Afrique Centrale in Tervuren, Belgium. In addition, data were collected on the small but extremely well-documented skeletal sample from Gombe National Park (N=14 crania, 13 postcrania — including adults and adolescents). Cranial injuries, including healed fractures and bite wounds, were fairly frequent in the museum collection of chimpanzees (5.5% of individuals), but were twice as frequent in gorillas (11.0%). In the Gombe sample an even higher incidence was observed (28.6% of individuals). Bonobos, however, showed the lowest incidence of cranial trauma found among any of the African ape samples (1.4% of individuals). Postcranial trauma, documented most clearly by healed fractures, was seen in 21.7% of the Powell-Cotton chimpanzees, 30.8% of Gombe chimpanzees, 17.7% of gorillas, and in 13.3% of bonobos. Most of these lesions were found in the upper appendage. Nevertheless, highly debilitating healed fractures of the femur were also noted, most frequently and severe in female gorillas. The pattern of injuries suggests serious risks of falling in all free-ranging African apes, but also (in chimpanzees and gorillas) considerable risk from interindividual aggression, especially for males.     

Development of guidelines for assessing obesity in captive chimpanzees (Pan troglodytes)

Many captive chimpanzees (Pan troglodytes) are subjectively considered to be overweight or obese. However, discussions of obesity in chimpanzees are rare in the literature, despite the acknowledged problem. No study to date has systematically examined obesity in captive chimpanzees. This project develops guidelines for defining obesity in captive chimpanzees through the examination of morphometric and physiologic characteristics in 37 adult female and 22 adult male chimpanzees. During each animal's biannual physical exam, morphometric data was collected including seven skinfolds (mm), body mass index (BMI), waist‐to‐hip ratio (WHR), and total body weight (kg). The morphometric characteristics were correlated with triglycerides and serum glucose concentration, to test the utility of morphometrics in predicting relative obesity in captive chimpanzees. Abdominal skinfold (triglyceride: F=3.83, P=0.05; glucose: F=3.83, P=0.05) and BMI (triglyceride: F=10.42, p=0.003; glucose: F=6.20, P=0.02) were predictive of increased triglycerides and serum glucose in females; however no morphometric characteristics were predictive of relative obesity in males. Results suggest that no males in this population are overweight or obese. For females, there were additional significant differences in morphometric (skinfolds, BMI, WHR, total body weight) and physiologic measurements (systolic and diastolic blood pressure, red blood cells) between individuals classified overweight and those classified non‐overweight. Skinfold measurements, particularly abdominal, seem to be an accurate measure of obesity and thus potential cardiovascular risk in female chimpanzees, but not males. By establishing a baseline for estimated body fat composition in female captive chimpanzees, institutions can track individuals empirically determined to be obese, as well as obesity‐related health problems. Zoo Biol 0:1–12, 2007. © 2007 Wiley‐Liss, Inc.     

Densities,Distributions, and Seasonal Movements of Gorillas and Chimpanzees in Swamp Forest in Northern Congo

The conservation of gorillas (Gorilla spp.) and chimpanzees (Pan troglodytes) depends upon knowledge of their densities and distribution throughout their ranges. However, information about ape populations in swamp forests is scarce. Here we build on current knowledge of ape populations by conducting line transect surveys of nests throughout a reserve dominated by swamp forest: the Lac Télé Community Reserve in northern Congo. We estimated gorilla and chimpanzee densities, distributions across habitats, and seasonal changes in abundance. Gorilla density was 2.9 gorillas km^–2, but densities varied by habitat (0.3–5.4 gorillas km^–2) with highest densities in swamp forest and terra firma mixed forest. Average chimpanzee density is 0.7 chimpanzees km^–2 (0.1–1.3 chimpanzees km^–2), with highest densities in swamp forest. Habitat was the best predictor of ape nest abundance, as neither the number of human indices nor the distance from the nearest village predicted nest abundance. We recorded significantly greater numbers of apes in terra firma forest during the high-water season than the low-water season, indicating that many gorillas and chimpanzees are at times concentrated in terra firma forest amid a matrix of swamp forest. Seasonally high numbers of apes on terra firma forest islands easily accessible to local people may expose them to substantial hunting pressure. Conversely, the nearly impenetrable nature of swamp forests and their low value for logging makes them promising sites for the conservation of apes.     

Behavioral Ecology of Sympatric Chimpanzees and Gorillas in Bwindi Impenetrable National Park,Uganda: Diet

Via a field study of chimpanzees (Pan troglodytes schweinfurthii) and gorillas (Gorilla gorilla beringei) in Bwindi Impenetrable National Park, Uganda, we found that their diets are seasonally similar, but diverge during lean seasons. Bwindi chimpanzees fed heavily on fruits of Ficus sp., which were largely ignored by the gorillas. Bwindi gorilla diet was overall more folivorous than chimpanzee diet, but was markedly more frugivorous than that of gorillas in the nearby Virunga Volcanoes. During 4 mo of the year Bwindi gorilla diet included more food species than that of the chimpanzees. Three factors in particular—seasonal consumption of fibrous foods by gorillas, interspecific differences in preferred fruit species, and meat consumption by chimpanzees—contributed to dietary divergence between the two species. When feeding on fruits, gorillas ate Myrianthus holstii more frequently than chimpanzees did, while chimpanzees included more figs in their annual diet. Chimpanzee diet included meat of duikers and monkeys; gorilla frequently consumed decaying wood.     

The role of taste in food selection by African apes: implications for niche separation and overlap in tropical forests

Ripe fruit eating shapes the behavior of most of the apes. Gorillas (Gorilla gorilla) and chimpanzees (Pan troglodytes) are very different sizes and, consequently, have been traditionally viewed as ecologically distinct, but few studies have explored the behavioral and physiological foundations of their diets. Debate continues on the extent that large-bodied gorillas may be less selective and more opportunistic fruit eaters than chimpanzees. Taste responses have been predicted to relate to body size and digestive strategies. This study employs laboratory research on taste perception and discrimination among captive zoo-housed chimpanzees and relates it to previous work on gorillas to better characterize diets and niche separation among these apes. During the captive trials, differences were recorded in consumption patterns of water and varying concentrations of dilute aqueous fructose (sweet) and tannic acid solutions (astringent), compounds commonly found in wild foods. The chimpanzees exhibited similar preference thresholds for fructose (50 mM) to other primates studied. They exhibited slightly lower inhibition thresholds for tannic acid solutions than gorillas, but higher than smaller primates studied to date. These preliminary findings suggest that tannin tolerance may well be mediated by body size, though possible species differences in salivary proteins or other sensory differences remain to be explored. This research furthers our efforts to understand the roles of body size and physiological adaptations in shaping diet and niche separation of chimpanzees and gorillas.     

Ecological restoration in eutrophic Lake Wuli: A large enclosure experiment

A large-scale enclosure experiment for lake restoration was carried out in Lake Wuli, a northern bay of shallow and eutrophic Lake Taihu in China. The large enclosure with an area of 10 ha was set up in the littoral zone and was bordered by waterproof fabric which did not cover the sediments. Multiple approaches were used and included fish removal, piscivorous fish stocking, shoreline reconstruction, aquatic macrophyte planting, benthic macro-animal stocking, and silver carp cultivation in pens for reduction of cyanobacteria. The results showed that the coverage of aquatic macrophytes increased from 0% to 45.7%. Mean concentrations of TN and TP inside the enclosure from May 2004 to May 2008 were 22.2% and 26.0% of those outside, respectively. Secchi depth was 0.40 m outside the enclosures and 0.75 m inside. However, responses of phytoplankton to the restoration project lagged behind improvement of water quality and reestablishment of aquatic plants. The phytoplankton biomass gradually decreased after the third year of the restoration. Stocking piscivorous fish and planting submerged macrophytes could not increase zooplankton biomass and enhance graze pressure on phytoplankton, most likely due to high omnivorous fish density and lower nutrition inside the enclosure. Higher grazing pressure of zooplankton on phytoplankton was observed in May and October every year. Zooplankton to phytoplankton biomass ratios were significantly negatively correlated with phytoplankton biomass outside (r = −0.440, p < 0.01) and inside the enclosure (r = −0.336, p < 0.05) from February 2004 to March 2007. Therefore, phytoplankton biomass inside and outside the enclosure was lower in May and October. Higher grazing pressure of zooplankton on phytoplankton in spring may result in occurrence of the clear-water phase that facilitated growth of submerged macrophytes in the littoral in Lake Wuli, and a clear-water state and improved water quality would likely be sustained throughout the year after reestablishment of submerged macrophytes.     

The effect of medroxyprogesterone acetate on behavioural responses of captive female hamadryas baboons (Papio hamadryas)

Female hormonal contraception is considered here as an alternative to vasectomy for population control in social groups of captive hamadryas baboons (Papio hamadryas). While female hormonal contraceptive methods have been successful, behavioural effects of such agents represent a potential welfare concern. This study examined the effect of medroxyprogesterone acetate (MPA; 3.5 mg/kg) on perineal tumescence and behaviour in three social groups (total of 3 males, 22 females) of captive hamadryas baboons. The agent had little effect on social interactions such as grooming relationships, aggression and affiliation (all P > 0.05), but did cause a reduction in sexual behaviour (P < 0.001). Females-mounting-females and females receiving mounting was decreased during MPA treatment compared with the minimal tumescence phase (P < 0.001). Age strongly influenced the contraceptive's duration: there was a significant correlation between age and latency of return to oestrus post-MPA (r = 0.832, P < 0.001) with the latency increasing by 2.61 days per year of age on average. Age also influenced the frequency of behaviours such as affiliation and aggression (P < 0.001 and P = 0.044, respectively). The absence of adverse behavioural effects further supports the use of MPA in the hamadryas baboon, and its potential use in other non-human primates.     

The Choice to Access Outdoor Areas Affects the Behavior of Great Apes

Outdoor access is often cited as a critical component of appropriate housing for great apes in captivity, and although studies have shown that offering primates choices can improve welfare, choice to access specific areas has been empirically neglected. Behavioral data were collected on chimpanzees and gorillas housed in naturalistic enclosures while (a) restricted to an indoor enclosure and (b) permitted free access to an adjacent outdoor area. To isolate the factor of choice, only the sessions in which apes remained indoors were compared. With choice, chimpanzees showed more frequent social, F(1, 5) = 20.526, p = .006, and self-directed behaviors, F(1, 5) = 13.507, p = .014, and lower inactivity levels, F(1, 5) = 9.239, p = .029. Gorillas were more frequently inactive, F(1, 8) = 22.259, p = .002, and produced lower levels of object manipulation, F(1, 8) = 8.243, p = .021, and feeding, F(1, 8) = 5.407, p = .049. Results are consistent with an association between choice and the expression of species-typical and arousal behaviors in chimpanzees. The effects are less evident in gorillas, but this outcome may be buffered by the species' lower motivation to utilize the outdoor spaces. Findings highlight species-specific reactions to access to choice that may offer insight for enclosure design, management, and nonhuman animal welfare.     

Ape behavior in two alternating environments: comparing exhibit and short‐term holding areas

In many facilities, primates are voluntarily transferred between different enclosures on a daily basis to facilitate animal husbandry and exhibit maintenance. This procedure is particularly relevant in the management of great apes living in zoos, where the requirements of functional management must be balanced with the desire to maintain enriching and naturalistic exhibit enclosures that benefit ape residents and attract the visiting public. In these settings, examinations of ape behavior and welfare typically focus exclusively on activity in the primary exhibit area. However, physical, social and sensory experiences unique to each area may shape different patterns of behavior. In the current study, zoo‐living chimpanzees and gorillas were moved each day from exhibit areas to off‐exhibit holding areas for a short duration as a part of regular management procedures. Behavioral data indicated species‐specific reactions to the holding area, including increased aggression and self‐directed behavior by chimpanzees and increased activity and prosocial behavior among gorilla subjects. Both species showed more feeding‐foraging behavior while in the exhibit enclosure. Results suggest that holding areas may not meet all behavior needs of captive great apes and demonstrate the importance of including all components of the captive enclosure in comprehensive analyses of great ape behavior and welfare. Am. J. Primatol. 72:951–959, 2010. © 2010 Wiley‐Liss, Inc.     

驯养林麝(Moschus berezovskii)的繁殖节律:分娩定时及同步化

于2013年3—10月在四川马尔康麝场开展,记录了178例驯养林麝(Moschus berezovskii)的分娩,分析了其分娩定时、同步化及关键影响因素。结果表明,马尔康麝场的驯养林麝分娩发生于5—7月间,分娩期长达66d,平均分娩时间为5月25日(17.60±0.98,n=178),分娩季节(75%的分娩完成时间)长22d(即5月7日至5月28日间)。马尔康林麝分娩的强季节性是对当地季节性水热条件和食物资源的适应。驯养林麝的分娩时间与其年龄的相关不显著(r=-0.121,P=0.1060.05),虽亚成体雌麝(2—3岁)的分娩时间(5月26日,18.81±1.47,n=75)有迟于成体麝((4—9岁)(5月24日,16.97±1.41,n=95)和老龄雌麝(≥10岁)(5月21日,13.63±2.24,n=8)的趋势,但差异未达显著水平(P0.05)。此外,麝场各饲养区内的雌麝分娩时间格局无显著差异(P0.05),泥地基底的改装圈舍内的雌麝分娩(5月22日,15.31±1.48,n=62)略早于砖地基底的原装圈舍雌麝分娩(5月26日,18.82±1.27,n=116),差异未达显著水平(P0.05)。     

Seasonal Effects on Great Ape Health: A Case Study of Wild Chimpanzees and Western Gorillas

Among factors affecting animal health, environmental influences may directly or indirectly impact host nutritional condition, fecundity, and their degree of parasitism. Our closest relatives, the great apes, are all endangered and particularly sensitive to infectious diseases. Both chimpanzees and western gorillas experience large seasonal variations in fruit availability but only western gorillas accordingly show large changes in their degree of frugivory. The aim of this study is to investigate and compare factors affecting health (through records of clinical signs, urine, and faecal samples) of habituated wild ape populations: a community (N = 46 individuals) of chimpanzees (Pan troglodytes) in Kanyawara, Kibale National Park (Uganda), and a western gorilla (G. gorilla) group (N = 13) in Bai Hokou in the Dzanga-Ndoki National Park (Central African Republic). Ape health monitoring was carried out in the wet and dry seasons (chimpanzees: July–December 2006; gorillas: April–July 2008 and December 2008–February 2009). Compared to chimpanzees, western gorillas were shown to have marginally greater parasite diversity, higher prevalence and intensity of both parasite and urine infections, and lower occurrence of diarrhea and wounds. Parasite infections (prevalence and load), but not abnormal urine parameters, were significantly higher during the dry season of the study period for western gorillas, who thus appeared more affected by the large temporal changes in the environment in comparison to chimpanzees. Infant gorillas were the most susceptible among all the age/sex classes (of both apes) having much more intense infections and urine blood concentrations, again during the dry season. Long term studies are needed to confirm the influence of seasonal factors on health and parasitism of these great apes. However, this study suggest climate change and forest fragmentation leading to potentially larger seasonal fluctuations of the environment may affect patterns of ape parasitism and further exacerbate health impacts on great ape populations that live in highly seasonal habitats.