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.     

Another gorilla (Gorilla gorilla gorilla) recognizes himself in a mirror

Various attempts have been made to explain why gorillas (Gorilla gorilla gorilla) find it difficult to recognize their mirror image. One of the most oft-cited reasons is aversion to eye contact, which stops gorillas from looking into a mirror and thus prevents them from carrying out a suitable exploration that could lead to self-recognition. In the experimental design used here the subject was first habituated both to observers and to the mirror as an object before being exposed to the latter. The study was performed with a single subject who was well adapted to captivity and exhibited no aberrant behavior or signs of stress. The results revealed that the subject had no aversion to eye contact. He showed considerable interest in the mirror and appeared relaxed when faced with his image. He gave a positive response to the mark test.     

Nest Building in Captive Gorilla gorilla gorilla

Although various aspects of gorilla nest building have been described in wild populations, nest-building behavior of captive gorillas has not been subject to much scientific review. We observed nest building in 17 gorillas during three periods: summer baseline, winter baseline, and winter treatment, in which the amount of available nesting material was doubled. We conducted observations exclusively in the indoor holding area in the hour following evening departure of animal care staff. During baseline, gorillas engaged in nest-building on 3.1% of scans and were on a constructed nest on 27.9% of scans. Overall, gorillas spent significantly more time on elevated nests than on floor nests. There were no statistically significant sex, age class, or rearing history differences in nest building, time spent on a nest, or nest location preference. Nest building consisted of both gathering and manipulating materials. The gorillas spent significantly more time building nests in winter than in summer. Additionally, they were more often on elevated nests during winter than summer. Doubling the amount of nesting material did not increase nest building, but it increased the number of floor nests. Our results suggest that providing adequate materials to captive gorillas for nest building may facilitate performance of species-typical nest-building, minimize competition among individuals for nesting sites and materials, and permit individual thermoregulation.     

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%).     

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.     

Insectivory by Gorilla gorilla gorilla in Southeast Cameroon

Our study extends quantitative analyses of insect-eating by gorillas (Gorilla gorilla gorilla) to Cameroon. During a 2-mo period (May–June 2001), we recorded and analyzed feeding traces on plants and insects and in gorilla feces. We found 180 feeding traces, 17% of which involved insectivory. Seventy-eight percent of the fecal samples (n = 36) contained insects. Ants were found in 61% of the samples, termites in 39%, while 56% of the samples contained remains of other insects. We added 14 new species to the known insect diet of western lowland gorillas. Overall, social insects are predominant. The choice of prey by the Ntonga gorillas gives new clues for the existence of cross-cultural differences among gorilla populations. A comparison of the overall frequency of insectivory with those at other sites in Central Africa indicate a possible effect of forest disturbance on the insectivorous behavior of gorillas. The study suggests the existence of temporal variation in ant- and termite-eating by gorillas.     

Seed dispersal effectiveness of the western lowland gorilla (Gorilla gorilla gorilla) in Gabon

The quantitative and qualitative aspects of seed dispersal by the western lowland gorilla (Gorilla gorilla gorilla) were investigated in Gabon. Fresh faeces were collected and washed to identify and count the seeds. Seed germinability after gut passage was estimated with trials in a nursery at the study site. To assess the impact of gut passage on germination success and delay, comparative trials were run with four treatments: (i) gut passed seeds cleaned of faeces, (ii) gut passed seeds within a faecal matrix, (iii) seeds from fresh fruits surrounded by pulp, and (iv) seeds from fresh fruits cleaned of pulp. The analysis of 180 faecal units resulted in the identification of 58 species of seed. Germination trials were realized for 55 species and the mean germination success reached 46%. The impact of gut passage was investigated for Santiria trimera and Chrysophyllum lacourtianum; both species displayed higher germination success after ingestion. This study shows that gorillas effectively disperse seeds of numerous plant species, many of which provide timber or nontimber forest products or are typical of Gabonese forests. Considering the high‐quality of gorilla deposition sites, gorillas is thought to play a unique role in the dynamics of Central African forest.     

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.     

Sexual and Hormonal Cycles in Geriatric Gorilla gorilla gorilla

As our closest living relatives, great apes likely experience behavioral and physiological patterns associated with reproductive aging and menopause that are similar to human patterns. We present results from a nationwide zoo-based study on behavioral and hormonal changes in female western gorillas. We evaluated progestogen concentrations via daily fecal sampling in 30 gorillas, 22 of which were geriatric (≥30). We collected concurrent behavioral data 1–3 times weekly on 16 of the females. While control females cycled regularly, ca. 23% of geriatric females are acyclic (menopausal), and another 32% show variable hormonal patterns suggesting perimenopause. Patterns included increased variability in cycle length and peak progestogen values, and frequent insufficient increases in progestogen levels during the luteal phase. Acyclic females have significantly lower overall progestogen concentrations than the self cycling females, though differences are not significant when cycle phase is incorporated. We detected behavioral estrus in 9 of 10 cycling females for which data were available. In all but 1 case, proceptive behavior occurred during the follicular phase, preceding ovulation on average by 6.6 d. Females spent more time in proximity to the silverback male while in behavioral estrus than during other periods. To date, maximum longevity in captive female gorillas is 52 yr, with poor reproductive prognosis beginning from the age of 37. We demonstrate that both perimenopause and menopause characterize aged female gorillas, which may experience a postreproductive lifespan of >25% of their lives. Continued study of aging apes is warranted, and apes may serve as models for age-related reproductive changes in humans.     

Development of Independence from the Mother in Gorilla gorilla gorilla

In gorillas, the mother takes full responsibility for carrying and feeding offspring, and lactational amenorrhea prevents her from investing in another offspring while suckling. Therefore, mothers should encourage immature gorillas to become gradually more independent until they are physically able to acquire sufficient resources, travel independently, and manage social relationships unaided. We investigated the development of independence in a population of wild western gorillas (Gorilla gorilla gorilla) at Mbeli Bai, Nouabalé-Ndoki National Park, Republic of Congo. We observed the spatial proximity, the development of travel, patterns of suckling and weaning, and the nature of mother-offspring interactions for 42 immature gorillas to investigate the nature of the relationship between mother and offspring. Though mother-offspring distance and independent travel increased during immaturity, with few active interactions between the dyads, offspring still continued to suckle until a median age of 4.6 yr, longer than in mountain gorillas. The tolerance of the mother toward suckling by older offspring may reflect the importance of continued nutritional investment: the temporal nature of the diet of western gorillas means that succulent fruits—likely to be preferred weaning foods—are not always available. We propose that to buffer against potential fruit shortage, mothers continue to nurse their offspring to decrease the likelihood of death from care-dependent factors and to improve an offspring’s chances of survival.     

Birth of a Western Lowland gorilla (Gorilla gorilla gorilla) following in vitro fertilization and embryo transfer

A 21-year-old multiparous female exhibiting 31–41 day menstrual cycles was given hFSH (225 IU/day, Metrodin 75, from cycle day 3 through 9 (menses = day 1) and hCG (10,000 IU, Profasi, on day 10 to stimulate follicular development. At 35 h after hCG, under isoflurane (AErrane) anesthesia, follicles were aspirated by controlled suction under transvaginal ultrasound guidance. Metaphase II oocyctes (n = 11) were placed in modified human tubal fluid (mHTF, 100 μl) medium under oil at 37°C in humidified 5% CO₂. Frozen semen, collected by voluntary ejaculation, was thawed (70°C H₂O bath, 6 sec), diluted slowly, centrifuged, and resuspended in mHTF, and 160,000 motile spermatozoa/ml were added at 6 h after oocyte recovery. At 21 h postinsemination (p.i.) eight oocytes were at the two-cell stage, five were cryopreserved, and three were cultured to the six- to eight-cell stage in mHTF with granulosa cells before transcervical uterine transfer at 47 h p.i. using a Teflon catheter. Micronized progesterone (400 mg/d) was orally administered for 10 weeks posttransfer (p.t.). Ultrasound examination revealed a single fetus at 15 weeks p.t., and unassisted delivery of a live 1.37 kg female infant occurred at 29 weeks. Am. J. Primatol. 41:247–260, 1997. © 1997 Wiley-Liss, Inc.     

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

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

Management of respiratory complications in a western lowland gorilla (Gorilla gorilla gorilla) born by cesarean section

A female western lowland gorilla (Gorilla gorilla gorilla) infant was delivered by cesarean section (C‐section) to an 18‐year‐old primiparous dam after prolonged labor. The infant required resuscitation at birth and was hospitalized for management of pneumonia and associated respiratory distress secondary to the aspiration of meconium‐stained amniotic fluid. The infant received nine days of intensive care with respiratory support, antibiotics, intravenous fluid therapy, anti‐inflammatory drugs, bronchodilators, and chest physiotherapy. Respiratory support included nasal continuous positive airway pressure (CPAP), and supplemental oxygen. Complications included right lung atelectasis secondary to bronchial obstruction and pneumonia. Following the resolution of pneumonia, visual reintroductions with the troop were initiated. The dam was given a medical lactation supplement (metoclopramide) and her mammary glands were stimulated to increase milk production. After several days of visual and olfactory introductions, the infant was successfully physically reintroduced to her dam at 12 days of age; the dam showed appropriate maternal response and nursing of the infant. The infant had appropriate growth and development, and 4 years later, has no evidence of negative side effects of neonatal respiratory disease. This is the first reported case of management of neonatal gorilla respiratory disease associated with a C‐section, with successful reintroduction to the family group after hospitalization.     

Discovering gorilla

On July 16, 1847, a missionary newly arrived in New York City from West Africa packed a collection of bones in a box and shipped them off to a colleague in Massachusetts. In a letter, Thomas S. Savage (Fig. 1), a graduate of Yale College and Yale Medical School, admitted to being “quite unwell,” probably meaning “utterly wretched.” He had already endured tropical diseases in Liberia off and on for more than a decade, and he'd seen his first two wives languish and die there, probably of malaria. He wasn't the sort to complain lightly.