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.     

Infant cradling in a captive mother gorilla

The purpose of the study presented here was to investigate the handedness and cradling preferences of a mother gorilla (Gorilla gorilla) from the Metro Toronto Zoo. The study also examined preferences for handedness for each member of the captive group. Observational data were collected using scan sampling at 60‐sec intervals. Handedness was determined with a coordinated bimanual tube test using peanut butter spread on the interior of a PVC tube. Our findings were largely consistent with the literature on laterality in African apes by documenting a left‐side cradling bias for one apparently ambidextrous captive gorilla mother. This bias was associated with a left head positioning preference by her infant. Although based on a single mother/infant pairing, this study indicates that cradling bias is not always determined by maternal handedness. Zoo Biol 27:420–426, 2008. © 2008 Wiley‐Liss, Inc.     

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.     

Adoption of an additional infant by a Western lowland gorilla (Gorilla gorilla gorilla).

A 10-year-old Western lowland gorilla, already caring for her own 14-month-old son, adopted a female neonate. The infant's mother (aged 7 years, 4 months) showed no interest in the infant, and it is unclear whether she abandoned the infant or whether it was seized by the dominant foster-mother. The foster-mother gave more maternal attention to the adoptee than to her own son but gave both infants the same protection. She adjusted her forms of transport to the age of each infant. The subadult mother of the neonate did not seek contact with her offspring during the first 4 weeks and in fact showed more interest in the 14-month-old male infant. Interactions between the two mothers were rare. The foster-mother's own male infant died 2 months after she had adopted the female infant. She looked after the adopted infant for 1 year, but then lost interest so that the adoptee had to be separated.     

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.     

Periparturitional behavior of a primiparous lowland gorilla

The behavioral interactions of a primiparous lowland gorilla and her newborn female infant were observed and recorded during the birth of the infant and the subsequent 27 hours. The mother's behavior, initially unresponsive to the infant, progressed rapidly through a series of interactions that are described as preliminary to, and perhaps essential for the ultimate development of appropriate maternal behavior. The relationship between different critical activities, such as: (1) the ingestion of birth fluids by the mother and the establishment of initial contact with the infant, (2) the progression from impersonal contact to ventral-ventral contact, and (3) the coordination between the mother's and infant's vocalizations and activity preceding nursing are described, analyzed, and interpreted.     

The birth of a wild mountain gorilla (Gorilla gorilla beringei)

The live birth of a wild mountain gorilla is described. Details of the birth process are given along with the mother’s periparturitional behaviour and the responses of others to the birth. The mother, a multiparous female, gave no observable indication that birth was imminent, and delivered her infant quickly and easily. During parturition, a subadult male showed interest in the proceedings. Following delivery, several animals approached the mother, who then left the birth site. The mother cleaned her infant and by two hours postpartum had established ventro-ventral contact and, possibly, nursing. These data are related to relevant observations from the literature and unpublished data on other animals from this study.     

Molecular systematics for taxonomic placement of a gorilla of uncertain origin

An adult male gorilla was donated from private ownership in 1994 to Zoo Atlanta and became part of the American Zoo and Aquarium Association's Gorilla Species Survival Plan. This animal, Ivan, was captured as an infant in Africa in 1964. Ambiguity regarding origin and concomitant sub‐species designation was resolved by analyzing the cytochrome oxidase II mitochondrial gene known to contain eight diagnostic sites for gorilla sub‐species. Ivan has the diagnostic profile that characterizes the western clade Gorilla gorilla gorilla. Zoo Biol 18:429–432, 1999. © 1999 Wiley‐Liss, Inc.     

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.     

Socialization processes in a female lowland gorilla

A low-interactive, captive, female lowland gorilla, Molly, was studied following the introduction into her enclosure of three gorillas, two males and a female, raised from birth in captive gorilla groups. Observations were made 6 mo after the new gorillas were introduced. Throughout the period of observation, Molly interacted in an affiliative manner with one of the males, playing or sitting quietly with him in a tree (where Molly spent most of her time) and occasionally on the ground. Agonistic displays between Molly and the new female decreased after they were released in the enclosure without the males for a series of days. Molly, however, continued to react to the other male, the most dominant, in an agonistic manner, and usually retreated from his reach, climbed the tree, and/or grimaced and piloerected whenever he approached. Although Molly's continued avoidance of the dominant male impeded her complete socialization, we propose that the interventions employed in this study—introduction of new younger gorillas into and an enclosure, and a series of dyadic separations between the noninteractive gorilla and each of the new group members—are possible strategies that can be used to facilitate socialization of captive, noninteractive gorillas.     

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.     

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.     

Managing the socialization of an adult male gorilla (Gorilla gorilla gorilla) with a history of social deprivation

Most non‐human primates exhibit aggression during changes in social group composition. In zoological parks, group membership changes are necessary for optimal population management, but can elicit problematic aggression. Furthermore, some primates with a long history of social deprivation are hyperaggressive when introduced to conspecifics. In this study of one male gorilla with a 30‐year history of social deprivation, we assessed the rate of aggression quantitatively during a four‐step socialization procedure. We hypothesized that 1) the frequency of agonistic/display behaviors would increase markedly at the beginning of each phase of the socialization, then decline to baseline levels over time in each phase and 2) the frequency of affiliative behaviors would not vary systematically within or between phases of socialization. Our results largely supported these predictions, and we found the four‐step socialization process effective in managing aggression in this case. In addition to documenting the successful socialization of a socially deprived adult male gorilla, we believe that the empirical process used in this case argues for scientific management of other introductions. Zoo Biol 20:347–358, 2001. © 2001 Wiley‐Liss, Inc.     

Relationship between behavior, adrenal activity, and environment in zoo-housed western lowland gorillas (Gorilla gorilla gorilla)

Monitoring adrenal activity through noninvasive fecal hormone sampling is rapidly gaining popularity as a tool to assess zoo animal welfare. However, few studies have sought to investigate the interrelationships between behavior, adrenal activity, and environment, and ask whether both behavioral and adrenal monitoring strategies are required to assess welfare sufficiently. We present the findings of a 9-month study of a small group (one male, two females) of Western lowland gorillas, Gorilla gorilla gorilla. First, we examined the effect of environmental variables on gorilla behavior. Second, we examined the effect of environmental variables on the concentration of fecal glucocorticoid metabolites (FGC) and the relationship between behavior and FGC. Environmental variables had similar effects on all three gorillas. Negative vigilance of visitors (NVV; staring, posturing, and charging at visitors) significantly increased in all subjects as environmental noise levels increased, and food-related behavior significantly decreased in all subjects as crowd size increased. Exhibit modifications had a number of positive effects on behavior. Notably, when privacy screens were used, NVV significantly decreased in two subjects. We found no significant effects of environmental variables on FGC. However, we did find significant relationships between behavior and FGC in one female. Specifically, her NVV was significantly higher one day before, and on the same day as, raised FGC. Also, hair plucking significantly increased in the two days following raised FGC. Overall, this study demonstrates how concurrent noninvasive fecal and behavioral monitoring can be used for gorilla welfare assessment.     

Mirror mediated object discrimination and self-directed behavior in a female gorilla

Mirror mediated object discrimination was investigated in a captive female, human-reared, western lowland gorilla (Gorilla gorilla gorilla) approximately 26 years of age. The gorilla was trained to find a stimulus that was only visible by use of the mirror. The gorilla could not reach the goal object except by observing it in the mirror and her hand movement was not visible through the mirror. Further, it was hypothesized that this mirror mediated object discrimination would enhance the probability of self-directed behavior.Gallup’s (1970) marking paradigm, excluding the use of general anesthesia, was utilized in assessing self-directed behavior. Mirror-gazing, face-directed, and mark-directed behavior with a mirror were compared before versus after discrimination mirror training. The results supported the hypotheses that gorillas are capable of mirror mediated object discrimination and that mirror training involving a discrimination task would facilitate self-directed behavior.     

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.     

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.     

Stability of the gorilla microbiome despite simian immunodeficiency virus infection

Simian immunodeficiency viruses (SIVs) have been discovered in over 45 primate species; however, the pathogenic potential of most SIV strains remains unknown due to difficulties inherent in observing wild populations. Because those SIV infections that are pathogenic have been shown to induce changes in the host's gut microbiome, monitoring the microbiota present in faecal samples can provide a noninvasive means for studying the effects of SIV infection on the health of wild‐living primates. Here, we examine the effects of SIVgor, a close relative of SIVcpz of chimpanzees and HIV‐1 of humans, on the gut bacterial communities residing within wild gorillas, revealing that gorilla gut microbiomes are exceptionally robust to SIV infection. In contrast to the microbiomes of HIV‐1‐infected humans and SIVcpz‐infected chimpanzees, SIVgor‐infected gorilla microbiomes exhibit neither rises in the frequencies of opportunistic pathogens nor elevated rates of microbial turnover within individual hosts. Regardless of SIV infection status, gorilla microbiomes assort into enterotypes, one of which is compositionally analogous to those identified in humans and chimpanzees. The other gorilla enterotype appears specialized for a leaf‐based diet and is enriched in environmentally derived bacterial genera. We hypothesize that the acquisition of this gorilla‐specific enterotype was enabled by lowered immune system control over the composition of the microbiome. Our results indicate differences between the pathology of SIVgor and SIVcpz/HIV‐1 infections, demonstrating the utility of investigating host microbial ecology as a means for studying disease in wild primates of high conservation priority.     

A survey of the apes in the Dzanga-Ndoki National Park, Central African Republic: a comparison between the census and survey methods of estimating the gorilla (Gorilla gorilla gorilla) and chimpanzee (Pan troglodytes) nest group density

A survey of apes was carried out between October 1996 and May 1997 in the Dzanga sector of the Dzanga‐Ndoki National Park, Central African Republic (CAR), to estimate gorilla (Gorilla gorilla gorilla) and chimpanzee (Pan troglodytes) densities. The density estimates were based on nest counts. The strip transect census and the line transect survey method (Standing Crop Nest Count) were used to estimate the gorilla nest group density. The strip transect has been most commonly used to date. It assumes that all nest groups within the width of the strip are detected, but as this assumption is easily violated in the dense tropical rain forest, the line transect survey was also used. In this method, only the nest groups on the transect line itself should be detected. This method proved to be an adequate and easy technique for estimating animal densities in dense vegetation. The gorilla density of 1.6 individuals km^?2 (line transect survey method) found for the Dzanga sector is one of the highest densities ever reported in the literature for the Western lowland gorilla. The density estimate for chimpanzees was 0.16 individuals km^?2 (census method). The results of this study confirm the importance of the Dzanga‐Ndoki National Park for primate conservation.     

Sexual behavior in female western lowland gorillas (Gorilla gorilla gorilla): evidence for sexual competition

Previous research in gorillas suggests that females engage in post‐conception mating as a form of sexual competition designed to improve their own reproductive success. This study focused on sexual behaviors in a newly formed group of western lowland gorillas (Gorilla gorilla gorilla) housed at Zoo Atlanta. All females engaged in mating outside their conceptive periods, although there was individual variation in the frequency of the behavior. An analysis of the presence/absence of sexual behavior found females, regardless of reproductive condition, were more likely to engage in sexual behavior on days when other females were sexually active. On these “co‐occurrence” days, females were significantly more likely to solicit the silverback, but copulations did not differ from expectation. The results find further evidence for sexual competition among female gorillas and suggest that this may occur throughout their reproductive cycle rather than only during pregnancy. Am. J. Primatol. 71:587–593, 2009. © 2009 Wiley‐Liss, Inc.