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.     

Behavioral responses of an infant gorilla to maternal separation in a captive social group of lowland gorillas (Gorilla gorilla gorilla)

The present report describes behavioral reactions of a 33-month-old female infant gorilla to maternal separation in a captive social group whose composition is similar to that of wild groups. The infant gorilla responded differently to two types of maternal separation. When she remained alone for a few hours, she cried repeatedly and moved restlessly, indicating protest. Upon reunion and also for a few days thereafter, an intensification of the mother-infant relationship occurred. On the other hand, when she was separated from her mother but remained with the other group members for nine days, she did not display any behaviors that could be characterized as protest, but rather showed clear behavioral depression. During the 9-day separation period, she hardly played with other group members but she developed affiliative relationships with the leading male. After the reunion from the 9-day separation, she spent as much time near her mother as before separation and played with other infants at a level similar to that before separation, while she sometimes displayed behavioral patterns demanding the maintenance of physical contact with her mother. The present findings are compared with other reports in great apes and human children.     

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.     

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.     

Cervical necrotizing fasciitis and myositis in a western lowland gorilla (Gorilla gorilla gorilla)

A 39-yr-old wild-caught, female western lowland gorilla ( Gorilla gorilla gorilla ) died during an immobilization to assess swelling and apparent pain of the cervical region. Necropsy revealed a fistulous tract containing plant material in the oropharynx, above the soft palate, communicating with a left-sided cervical necrotizing fasciitis and myositis. Alpha-hemolytic Streptococcus and Prevotella sp. were isolated from the cervical lesion . This is a report of cervical necrotizing fasciitis in a western lowland 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.     

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%).     

Olfactory discrimination in the western lowland gorilla, Gorilla gorilla gorilla

The olfactory abilities of great apes have been subject to little empirical investigation, save for a few observational reports. This study, using an habituation/dishabituation task, provides experimental evidence for a core olfactory ability, namely, olfactory discrimination, in the gorilla. In Experiment 1, six zoo-housed western lowland gorillas were individually presented with the same odour on four trials, and with a novel odour on the fifth trial. Odours (almond and vanilla) were presented on plastic balls, and behavioural responses of sniffing and chewing/licking the balls were recorded. A second experiment presented the same odour on four trials and no odour on the fifth to examine whether any dishabituation was due to the presence of a new odour or the absence of the familiar odour. Gorillas habituated their behaviour with repeated presentation of the same odour, but dishabituated, i.e. increased sniffing and chewing/licking, when presented with the novel odour. No dishabituation was noted when using water as the stimulus across all trials or when used as the novel odour. Overall, results show that gorillas are able to discriminate between odours.     

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.     

The genetic and demographic status of the Western lowland gorilla (Gorilla g. gorilla) in captivity

There are over 600 gorillas in captivity of which 43% are now captive born. Because the wild population is threatened and trade represents a major threat to its long-term survival, the captive population needs to be managed to be demographicalry stable over the long term, while retaining a substantial amount of genetic variation. Projected trends in population size and structure, based on recent fecundity and survival rates, suggest that the captive population will decline slowly unless infant mortality rates can be reduced. From a genetic standpoint, however, the large number of wild-born animals and large population size suggest that there should be no difficulty in achieving genetic aims to preserve 90% heterozygosity over the next 200 years.     

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.     

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...     

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.     

A case study of primiparous maternal and infant gorilla (Gorilla gorilla gorilla) behavior

A primiparous mother and her infant were subjects of a longitudinal behavioral study at Lincoln Park Zoo in Chicago, Illinois. From November 1998 to November 1999, we collected a total of 100 hr of focal nonhuman animal instantaneous point sampling and all occurrence data on the mother and her infant. After 8 months, we introduced the 4-member focal group to an 8-member gorilla group, thus providing an opportunity to study the effect of the introduction on mother-infant behavior. Overall, time the pair spent physically apart was notably high with contact and proximate scores steadily decreasing over time. The infant was largely responsible for maintaining social proximity, rarely leaving the mother and frequently approaching her. In contrast, the mother left the infant frequently and approached the infant minimally. Maternal affiliative and nonaffiliative behaviors fluctuated throughout the study. Over time, both decreased. Despite a precarious maternal relationship, infant developmental trends were typical for captive gorillas. The results of this study suggest that allowing flexibility in judging maternal conduct can be of benefit to successful gorilla husbandry.     

Third-Party Intervention in Wild Western Lowland Gorillas (Gorilla gorilla gorilla)

International Journal of Primatology -     

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.     

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.