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.     

Fatal ulcerative colitis in a western lowland gorilla (Gorilla gorilla gorilla)

A captive western lowland gorilla (Gorilla gorilla gorilla) presented with watery diarrhoea that progressed to become profuse and haemorrhagic. Faecal analyses revealed Balantidium (B.) coli trophozoites and salmonella-like bacteria. Despite treatment the gorilla died on the 5th day after onset of symptoms. Post-mortem examination revealed a severe erosive-ulcerative superficial and deep colitis. Histological examination of post-mortem samples of the colon showed plentiful B. coli invading into the mucosa and submucosa, whilst PCR screening of bacterial DNA could not confirm any bacteria species which could be connected to the clinical picture. As B. coli is usually a non-pathogenic gut commensal, and as this animal previously showed evidence of non-symptomatic infection of B. coli, it is possible that the switch in pathogenicity was triggered by an acute bacterial infection. Despite successful treatment of the bacterial infection the secondary deep invasion of B. coli was not reversed, possibly because of the failure of the treatment regimen, and led to the death of the gorilla.     

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.     

Spatial memory and foraging competition in captive western lowland gorillas (Gorilla gorilla gorilla)

Spatial memory and foraging competition were investigated in three mother/offspring pairs of western lowland gorillas,Gorilla gorilla gorilla, using a naturalistic foraging task at the Toronto Zoo. Sixteen permanent food sites were placed throughout the animals’ enclosures. All of the sites were baited and a pair of animals was free to visit the sites and collect the food. Five of the subjects collected the food with accuracy better than chance. Most of the subjects visited the sites using a pattern, and for half the subjects this was one of adjacency. The high accuracy of five of the subjects and the lack of a consistent adjacency pattern suggest that the animals did in fact use spatial memory. Furthermore, the gorillas tended to avoid visiting food sites that had been previously depleted by their partner. They also appeared to split their search of the enclosures, each visiting only a proportion of the food sites. This indicated that the animals were competing and altering their foraging behaviour based on the behaviour of their partner. Therefore, accuracy was recalculated to take this into account. When the sites depleted by either animal in a pair during a given trial were worked into the accuracy calculations for individual animals, three of the animals still maintained accuracy above chance. This suggests that the animals were not only able to remember which sites they had depleted, but those sites depleted by their foraging partner as well.     

Deception and hiding in captive lowland gorillas (Gorilla gorilla gorilla)

Deception and hiding are described for a group of captive lowland gorillas comprising two adult males, one female, and her infant. The males repeatedly interacted with the infant, and their interest was repeatedly thwarted by the mother. As in other social situations in which one animal controls access to an object desired by another, deceit was used to thwart the other's control. Either one or both males at times concealed their actions toward the infant, inhibited their attention to the infant, created a neutral image to get the infant, or interacted with the infant to tease the mother.     

A training program for noninvasive semen collection in captive western lowland gorillas (Gorilla gorilla gorilla)

Staff at Omaha's Henry Doorly Zoo devised a training program for noninvasive semen collection from three male gorillas. Trained behaviors, shaped using food rewards and verbal praise, enabled the trainer to perform a cursory physical examination and collect >270 semen samples during the study period. Ejaculate volume, sperm motility, and progressive forward motion were recorded. Two of the gorillas regularly produced semen samples that were cryopreserved. Frozen semen from one gorilla was successfully used in an assisted reproductive procedure. The training program may be used as a guideline for other institutions to create similar programs. Zoo Biol 17:143–151, 1998. © 1998 Wiley-Liss, Inc.     

Endoparasites of western lowland gorillas (Gorilla gorilla gorilla) at Bai Hokou, Central African Republic

A coprologic study of free-ranging western lowland gorillas (Gorilla gorilla gorilla) at Bai Hokou, Dzangha-Ndoki National Park, Central African Republic (2 degrees 51'34'N, 16 degrees 28'03'E) was conducted from October 1999 to November 2000. All 75 fecal samples examined were positive for endoparasites, and each contained at least two species. Parasites present included two genera of amoebae, entodiniomorph ciliates, including Prototapirella gorillae, Troglodytella spp., and Gorillophilus thoracatus, a Balantidium-like organism, strongyle/trichostrongyle eggs (including a presumptive Mammomonogamus sp. and several other genera), Strongyloides sp., Probstmayria sp., a spirurid, a trichuroid, and several unidentified trematodes. Flagellates and cestodes were not found. Despite the presence of a variety of parasite genera, in general, levels of parasitism were low. These data provide baseline parasitologic data for this population as part of a comprehensive health-monitoring program. With the advent of ecotourism in this study area, continued monitoring is indicated for insuring the health of both gorillas and humans in the Bai Hokou study area.     

Fertility in the male gorilla (Gorilla gorilla): Relationship to semen parameters and serum hormones

Circulating levels of steroid and protein hormones were measured in 17 adult male lowland gorillas (Gorilla gorilla). The population included both fertile and infertile males as identified by previous siring of offspring and presence or absence of spermatozoa in the ejaculate obtained by rectal probe electrostimulation. Correlations were sought between levels of testosterone, dihydrotestosterone, androstenedione, estrone, estradiol, progesterone, 170H-progesterone, dihydroepiandrosterone, luteinizing hormone, follicle-stimulating hormone (FSH), and potential fertility status. The results identify normal circulating levels of these hormones, and indicate that aspermatogenesis and infertility are not necessarily associated with any alteration in levels of gonadal steroids. There is an association of aspermatogenesis with elevation of FSH. Levels of adrenal androgens are more similar to other non-human primates than to the human, which is of interest because in other aspects of reproductive physiology so far investigated the gorilla has proved to resemble the human more closely than it does the other nonhuman primates.     

Metastatic endocervical adenocarcinoma in a western lowland gorilla (Gorilla g. gorilla): no evidence of virus-induced carcinogenesis

Background Cervical Cancer is the second most common cancer among women. Nevertheless, similar tumours have only been rarely described in Great Apes. This report characterizes the pathological and molecular features of a metastatic endocervical adenocarcinoma in a Western lowland gorilla (Gorilla g. gorilla). Methods Necropsy and histopathology was performed to identify the cause of the disease in an cachectic 50‐year‐old western lowland gorilla. Immunohistochemistry for Ki67, oestrogen receptor alpha and ERBB2 was performed to characterize the tumor. In addition, Pan‐herpesvirus and Pan‐papillomavirus PCR were used to identify a possible viral cause. Results The endoccervical carcinoma showed a severe metastatic spread to the lung, brain and bone and was herpesvirus and papillomavirus‐negative. Most tumor cells were ERBB2‐positive, 15% of tumor cells were Ki67‐positive and only few tumor cells had oestrogen receptor alpha expression. Conclusions Histopathologically and immunohistochemically, the tumour had striking similarities to human endocervicial adenocarcinomas of the common type. However, PCR analysis failed to identify herpes‐ or papillomaviral DNA in the tumor at the time of necropsy, thus leaving the question for cause of the disease open.     

Growth and feeding relationships of a hand-reared lowland gorilla infant (Gorilla g gorilla)

A captive-born female lowland gorilla that was being hand-reared by a group of surrogate mothers in a public zoo was observed for her first 6 mo. Caloric intake and weight gain, along with feeding bias of surrogate mothers, were examined. Caloric intake was highest during early morning and late at night. The weekly caloric intake and weight gain fluctuated with no established pattern. Although the gorilla's caloric intake did not increase with age, her total weight increased with a slower growth rate in the latter part of the study period, indicating a decreased caloric intake/weight ratio. It became evident that each surrogate exhibited an “overfeeding” and “underfeeding” tendency; calories given by the surrogates varied considerably, reflecting the interaction between the infant and the surrogates.     

Electroejaculation and semen analysis in a male lowland gorilla,Gorilla gorilla gorilla

Two electroejaculations and a testicular biopsy were performed on a lowland gorilla,Gorilla gorilla gorilla, to determine fertility. Sperm morphology showed 92.5% abnormal sperm which were of primary, or testicular, origin. Testicular biopsy revealed abnormally shaped nuclei in the later stages of spermiogenesis, supporting the semen analysis performed from the electroejaculations. The majority of abnormalities consisted of pyriform heads (23%) and abnormal acrosomes (35%).     

ORIGINAL ARTICLE: Medical and surgical management of reproductive neoplasia in two western lowland gorillas (Gorilla gorilla gorilla)

Background Reports of female reproductive tract neoplasia are infrequent in great apes. Methods Two captive‐born, female western lowland gorillas (Gorilla gorilla gorilla) housed at the North Carolina Zoological Park were diagnosed with reproductive neoplasia. Results The first gorilla had uterine endometrial thickening and uterine fibroids diagnosed during a routine annual examination. Subsequently, the animal underwent several uterine curettage procedures in an attempt to debulk the uterine mass. Biopsy results indicated uterine adenocarcinoma. The animal was treated with an ovariohysterectomy followed by a combination of megestrol acetate and medroxyprogesterone acetate. The second gorilla was diagnosed with squamous cell carcinoma of the vagina, cervix, and uterus after presenting for intermittent vaginal bleeding of 1‐month duration. This animal underwent palliative radiation therapy, receiving two rounds of radiation treatment 8 weeks apart. Conclusions The following report describes the diagnosis and management of the two cases.     

Activity rhythm and the ranging of a solitary male mountain gorilla (Gorilla gorilla beringei)

To clarify the advantages of solitary life in gorilla males, a lone silverback mountain gorilla (Gorilla gorilla beringei) was studied for nine months in the natural habitat of the Virunga volcanoes. While the time budget for each activity and daily activity cycle were similar to those of groups, his daily journey distance and ranging patterns differed from those of groups. His movements were little influenced by the distribution and abundance of foods, which strongly influence the movements of groups. He notably increased his day journey distances when he encountered neighboring groups. He persistently followed the groups for days and went out of his usual range area. These encounters shifted his monthly range from his natal group's range to that of other groups. When the silverbacks of the encountered groups noticed his presence, they usually gave hoots and chest-beats and sometimes fought violently with him, while females and immatures did not show positive responses towards him. Lone males could have more chance to contact females and to lure them away from their groups than silverbacks within groups. The lone male stage, accompanied by frequent contacts with different groups, probably provides maturing males with useful knowledge of neighboring groups and areas.     

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.     

Adult–adult play in captive lowland gorillas (Gorilla gorilla gorilla)

Primates - Among African great apes, play is virtually absent between adult lowland gorillas (Gorilla gorilla gorilla). Here, we report an extremely rare case of adult–adult play observed in...     

The development of infant play in a captive group of lowland gorillas (Gorilla gorilla gorilla)

Three infant gorillas born at the Yerkes Regional Primate Research Center of Emory University were studied during their first year and one-half of life for various aspects of behavior, including solitary and social play, using both focal animal and one-zero sampling. The appearance of play in these infants followed a developmental trend, beginning with mother-infant play, and followed by solitary play, and then social play among peers. Mothers were initially very vigilant, repeatedly interrupting infant peer play bouts, this relaxing toward the end of the first year. Evidence for a possible sex difference in active social play is presented.     

Physical and activity changes associated with pregnancy in captive lowland gorillas (Gorilla gorilla gorilla)

The physical appearance and the behavior of five lowland gorilla females at two zoos were recorded before and during 14 pregnancies. Whereas only the quality of changes associated with pregnancy had been described previously, in this study the behavior of the females was recorded quantitatively and evaluated statistically. All females at Stuttgart showed distention of the abdomen three to four months before delivery and development of the breasts a few weeks before parturition. Milk was produced by the third month in one case, and in the sixth month or later in the others, sometimes after delivery. The female at Frankfurt stopped social play seven days after conception; the Stuttgart females, in general, stopped, in the first weeks of pregnancy. Social activity and locomotion decreased considerably within the first three months in all females and were significantly different between the pregnant and the nonpregnant state in all the Stuttgart females. In this study, as in others in the literature, behavioral changes were much more reliable signs of pregnancy than were physical changes. Thus the quantitative results confirm those obtained solely by qualitative observation.     

Spontaneous use of sticks as tools by captive gorillas (Gorilla gorilla gorilla)

The present report describes the spontaneous use of sticks, as tools by young adult gorillas (Gorilla gorilla gorilla) in a social group at the San Diego Wild Animal Park, CA, USA. Three 8-year-old gorillas (one female and two males) threw sticks into the foliage of trees, which the gorillas could not climb due to electric wire, to knock down leaves and seeds. Two of the three gorillas selected sticks that were more suitable (i.e. longer or thicker sticks) for throwing. Moreover, they looked up at the target (i.e. the foliage of the tree) before throwing and grasped the stick at a position appropriate, for throwing (i. e. the end of the stick). They were more likely to throw sticks when particular adult group members were not nearby. These two gorillas also pulled branches of trees toward themselves by using sticks to capture them (branch-pulling), and one of these two beat a branch with a stick to knock down leaves and seeds (branch-beating). One of these two gorillas used much longer sticks for branch-pulling than for stick-throwing, indicating that he was capable of task-dependent selection of sticks. Analyzing the spontaneous use of sticks as tools by gorillas in captivity can lead to a better understanding of not only their cognitive ability but also of their social relationships which may otherwise be concealed.     

Evaluation of different storage methods to characterize the fecal bacterial communities of captive western lowland gorillas (Gorilla gorilla gorilla)

Freezing is considered to be the best method for long-term storage of bacterial DNA from feces; however this method cannot be usually applied for samples of wild primates collected in the challenging conditions of the tropical forest. In order to find an alternative conservation method of fecal samples from wild great apes, we compared freezing with other fixation methods. Fecal samples from 11 captive gorillas (Gorilla gorilla gorilla) from three Czech Zoos were stored using freezing, RNA Stabilization Reagent (RNAlater), and 96% ethanol. Subsequently, the samples were examined using culture-independent methods (PCR-DGGE, and Real-time PCR) to qualitatively and quantitatively assess fecal microbiota composition and to compare differences among the storage methods. Noticeably, freezing samples resulted in the highest recoveries of DNA. No significant differences in DNA recovery were found between freezing and using RNAlater; however, significantly lower DNA concentrations were recovered from samples stored in 96% ethanol. Using PCR-DGGE we found that either 96% ethanol, RNAlater or freezing were suitable for preserving bacterial DNA; however fingerprints obtained from RNAlater storage were more similar to those obtained from the frozen method; in comparison to the patterns resulting from storing samples in ethanol. Using qPCR, frozen samples yielded the highest values of bacterial counts, with the exception of Enterobacteriaceae, which showed the highest numbers using samples stored in ethanol. Sequences of amplicons obtained from PCR-DGGE belonged to the families Clostridiaceae, Lactobacillaceae, Staphylococcaceae, and Lachnospiraceae, phylum Firmicutes; however most amplicons showed sequence similarity to previously uncultured microorganisms. Bacteria belonging to the phylum Firmicutes were the most frequently identified species in the fecal bacterial communities of captive western gorillas. The study showed that RNAlater is an optimal storage method when freezing is not possible.