Sex differences in play among western lowland gorilla (Gorilla gorilla gorilla) infants: implications for adult behavior and social structure

Mammalian play is believed to improve motor skills as well as facilitate the development of social relationships. Given the marked sexual dimorphism in gorilla body size and the role assumed by the male in protecting the group from conspecifics and predators, the motor-training hypothesis of play predicts that male infants should exhibit higher frequencies of social play than female infants, and that males should prefer to play with other males. Given that adult female gorillas are strongly attracted to adult breeding males and form only weak social bonds with unrelated adult females, the social-relationship hypothesis of play predicts that female infants should prefer to play with males. These hypotheses were tested in a 22-month study of 12 gorilla infants, aged between 0-5 years, living in three zoological parks in Chicago and Atlanta. Consistent with the hypotheses, male infants played more than female infants did, and both male and female infants preferred to play with males rather than with females. These findings suggest that sex differences in play in the great apes and other primates can be predicted by the characteristics of adult behavior and social structure above and beyond the patterns of sex-biased dispersal or coalition formation with same-sex kin.     

Social structure and life-history patterns in western gorillas (Gorilla gorilla gorilla)

Life-history traits and ecological conditions have an important influence on primate social systems. Most of what we know about the life-history patterns and social structure of gorillas comes from studies of eastern gorillas (Gorilla beringei sp.), which live under dramatically different ecological conditions compared to western gorillas (Gorilla gorilla sp.). In this paper we present new data on western gorilla social structure and life histories from four study sites, and make comparisons with eastern gorilla populations. Data were obtained from two study sites with gorilla groups undergoing the habituation process (Lossi, Democratic Republic of Congo and Bai Hokou, Central African Republic) and two "bai" studies (Maya Nord and Mbeli Bai, Republic of Congo). The size and structure of these groups were similar to those seen in eastern gorillas. However, differences in the occurrence of various group transitions (group formations, changes between one-male and multimale composition, and group disintegrations) exist, and western gorillas notably exhibit much higher rates of male emigration and correspondingly fewer multimale groups compared to mountain gorillas. Certain phenomena have been observed only rarely, including predation by leopards. The preliminary data show no significant differences in birth rates between western gorillas and mountain gorillas. The ecological variability across gorilla habitats likely explains the flexibility in the social system of gorillas, but we need more information on the social relationships and ecology of western gorillas to elucidate the causes for the similarities and differences between western and eastern gorillas on the levels of individuals, social groups, and population dynamics.     

Factors influencing the formation and maintenance of all‐male gorilla groups in captivity

The social housing of males is of particular importance for captive managers of polygynous species. In this work, we highlight nine areas we believe are important to the successful formation and maintenance of all‐male gorilla groups. Although more data are still needed to complete our understanding of these groups, the general picture that emerges is that all‐male groups can be a functional social unit for male gorillas, the longevity of which might be improved by careful planning. It appears that the best time to form all‐male groups is when the animals are still immature, as males in this age class have been observed to form some of the most stable groups. Efforts should be made to diversify the groups in terms of rearing history, particularly with respect to hand‐reared males, and to limit the amount of hand rearing experienced by males. Groups probably should contain no more than three or four adult males. Exhibits should be designed to provide visual barriers, refuges for subordinate animals, the means to separate individuals, and possibly the means to isolate all‐male groups from mixed‐sex groups. Additionally, because it is likely that some males will have to be removed from all‐male groups, zoos need to design facilities that provide state‐of‐the‐art housing for solitary individuals. It is hoped that by identifying bachelor males early in life and establishing cooperative management plans across institutions, zoos will be able to provide beneficial, long‐term social situations for all male gorillas in captivity. Zoo Biol 23:189–203, 2004. © 2004 Wiley‐Liss, Inc.     

Influences of Relatedness,Food Deprivation,and Sex on Adult Behaviors in the Group‐living Insect Forficula auricularia

The evolution of group living is generally associated with the emergence of social behaviors that ensure fitness benefits to group members. However, the expression of these behaviors may depend on group composition, which can vary over time with respect to sex, starvation status, and relatedness. Here, we investigated (1) whether adults of the group‐living European earwig, Forficula auricularia, show cooperative behaviors toward conspecifics and (2) whether sex, food availability, and relatedness shape the nature and frequency of these behaviors. We conducted a full‐factorial experiment using 108 unisexual pairs of adults, in which we manipulated these three factors and video‐recorded the earwig behaviors for 45 min. Our results revealed that adults mostly expressed self‐directed and aggressive behaviors. Nevertheless, they also showed allogrooming, a social behavior that offers scope for cooperation. Pairs of males displayed longer bouts of aggression and allogrooming (when it occurred) than pairs of females. Food deprivation had no effect on male behaviors, but females spent less time self‐grooming and walking when they were food deprived. Finally, low relatedness between adults did not influence any of the measured behaviors, but exacerbated frass production, possibly due to social stress. Overall, these results indicate the limited role of cooperation among F. auricularia adults during their group‐living phase.     

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.     

A preliminary behavioral comparison of two captive all-male gorilla groups

Gorillas live in polygamous harem groups, generally composed of one male, several adult females, and their offspring. With an equal numbers of male and female gorillas born in captivity, however, housing gorillas in social breeding units inevitably means that some males will not have access to female social partners. Thus, the future of the captive gorilla population depends on the collective ability of zoos to house equal numbers of males and females. This study examined the behavioral profiles of two all-male groups of captive lowland gorillas (Gorilla gorilla gorilla) to provide information on this type of housing situation. One group consisted of three subadult individuals, while the other consisted of two subadults and a silverback. Data were collected during two 6-month intervals, for a total of 284 hr. The behavioral profiles of the animals were stable over the course of the study but proximity patterns changed. Differences in feeding, solitary play, and object-directed behavior were found between groups, while no significant differences were observed in affiliative or agonistic social behavior. At both institutions, group cohesion appeared to be high, particularly between subadults; these individuals spent approximately 10% of their time engaging in social behavior and 25-50% of their time in close proximity (within 5 m). However, the Zoo Atlanta males spent significantly more time within 1 m and 5 m of each other than the Santa Barbara males, which may reflect a higher level of cohesiveness among members of the Zoo Atlanta group. The behavioral profiles of the animals in this study were similar to those found in bachelor groups of wild mountain gorillas. One notable exception was the absence of homosexual behavior between the silverback and subadults in Santa Barbara and the low frequency of this behavior between subadults in both groups. Although more longitudinal data are needed, these data suggest that all-male groups can be a feasible housing strategy for males at certain periods of their life span. Zoo Biol 20:27-40, 2001. Copyright 2001 Wiley-Liss, Inc.     

Gut microbiome composition and metabolomic profiles of wild western lowland gorillas (Gorilla gorilla gorilla) reflect host ecology

The metabolic activities of gut microbes significantly influence host physiology; thus, characterizing the forces that modulate this micro‐ecosystem is key to understanding mammalian biology and fitness. To investigate the gut microbiome of wild primates and determine how these microbial communities respond to the host's external environment, we characterized faecal bacterial communities and, for the first time, gut metabolomes of four wild lowland gorilla groups in the Dzanga‐Sangha Protected Areas, Central African Republic. Results show that geographical range may be an important modulator of the gut microbiomes and metabolomes of these gorilla groups. Distinctions seemed to relate to feeding behaviour, implying energy harvest through increased fruit consumption or fermentation of highly fibrous foods. These observations were supported by differential abundance of metabolites and bacterial taxa associated with the metabolism of cellulose, phenolics, organic acids, simple sugars, lipids and sterols between gorillas occupying different geographical ranges. Additionally, the gut microbiomes of a gorilla group under increased anthropogenic pressure could always be distinguished from that of all other groups. By characterizing the interplay between environment, behaviour, diet and symbiotic gut microbes, we present an alternative perspective on primate ecology and on the forces that shape the gut microbiomes of wild primates from an evolutionary context.     

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.     

Captive female gorilla agonistic relationships with clumped defendable food resources

Minimal feeding competition among female mountain gorillas (Gorilla gorilla beringei) has resulted in egalitarian social relationships with poorly defined agonistic dominance hierarchies. Thus, gorillas are generally viewed as non-competitive egalitarian folivores that have had little need to develop effective competitive strategies to access food resources. However, this generalization is inconsistent with more recent research indicating that most gorillas are frugivorous, feeding on patchily distributed food resources. The current study at Howletts Wild Animal Park, Kent, England, explores the effects of clumped and defendable foods on female gorilla agonistic relationships among three groups of western lowland gorillas (G. g. gorilla), conditions that are predicted to lead to well-differentiated agonistic dominance hierarchies among female primates. The Howletts gorillas foraged all day on low-energy/-nutrient, high-fiber foods widely distributed around their enclosure by the keepers. However, they also had periodic access to high-energy foods (e.g., nuts, raisins, strawberries, etc.) that the keepers would spread in a clumped and defendable patch. Frequencies of agonistic and submissive behaviors between females and proximity data were gathered. High-status females were found to monopolize the food patch and kept the low-status females at bay with cough-grunt threat vocalizations or by chasing them away. Agonistic interactions were initiated mostly by females of high status; these were directed towards females of low status and were generally not reciprocal. In addition, females of low status engaged in submissive behaviors the most often, which they directed primarily at females of high status, especially in response to aggression by the latter. Agonistic interactions between high- and low-status females had decided outcomes more often than not, with low-status females the losers. Competition over highly desirable foods distributed in defendable clumps at Howletts appears to have led to well-defined dominance relationships among these female gorillas.     

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.     

Social compatibility in a newly formed all‐male group of white crowned mangabeys (Cercocebus atys lunulatus)

Surplus males in primate captive populations are a common problem for zoos. Some captive breeding programs promote all‐male groups as an adequate option to house surplus males, but there have been few attempts to assess the feasibility of this management technique across primate species. The present study provides preliminary data regarding social compatibility within a newly formed all‐male group of four white crowned mangabeys (Cercocebus atys lunulatus). The study was conducted at the Valencia Zoo (Spain), where data on social behavior were collected over 6 months using continuous focal animal sampling for a total of 87 hr of observation. Results show that low intensity aggressive behaviors (facial threats) were expressed at high rates, whereas physical aggression (fights) rarely occurred. Aggression was more frequent among individuals belonging to the same age–gender class. Regarding affiliative behaviors, every individual actively sought proximity to all other group members through positive approaches, and although not all males carried out social grooming, every male was groomed by at least one group member. Our results suggest that the group was compatible socially because social relationships among the individuals were not neutral, and physical aggression occurred at low rates. The present study provides preliminary data supporting the feasibility of all‐male groups as a management option for surplus males in captive populations of white crowned mangabeys. Nevertheless, further studies are needed to be able to generalize both within and across species. Zoo Biol 0:1–7, 2007. © 2006 Wiley‐Liss, Inc.     

The effect of visitors on the behavior of zoo-housed western lowland gorillas (Gorilla gorilla gorilla)

Primates, especially apes, are popular with the public, often attracting large crowds. These crowds could cause behavioral change in captive primates, whether positive, neutral, or negative. We examined the impact of visitors on the behavior of six western lowland gorillas (Gorilla gorilla gorilla), observing the troop over 6 weeks during high season (4.5 hr/day, 35 days, May–July 2016). We used focal scan sampling to determine activity budget and enclosure usage, and focal continuous sampling to identify bouts of anxiety-related behavior (visitor-directed vigilance, self-scratching, and aggression). Both daily zoo-entry numbers (V_GATE) and instantaneous crowds at the exhibit (V_DENSITY) were measured. Overall, V_GATE had little effect across behaviors. However, consistent with the more acute time frame of measurement, V_DENSITY was a better predictor of behavior; at high crowd volumes, we observed significant group-level changes in activity budget (increased inactivity, increased locomotion, and decreased environment-related behaviors), increase in some anxiety-related behaviors, and decreased enclosure usage. Although contributing similar effects, it could not be determined if crowd numbers, composition, or noise most affected the troop, nor any chronic effects of exposure to large crowds. Nevertheless, our findings suggest that measures to minimize the impacts of large crowds at the exhibit would be beneficial. Furthermore, we highlight potential discrepancies between common methods for measuring visitor numbers: V_GATE is less sensitive to detecting visitor effects on behavioral indices than V_DENSITY. Future studies should appropriately match the biological time frame of welfare indicators and visitor measures used to ensure the reliability of findings.     

Impaired social contacts with familiar anesthetized conspecific in CA3‐restricted brain‐derived neurotrophic factor knockout mice

Familiarity is conveyed by social cues and determines behaviors toward conspecifics. Here, we characterize a novel assay for social behaviors in mice—contacts with anesthetized conspecific—which eliminates reciprocal interactions, including intermale aggression and shows behaviors that are independent of the demonstrator's activity. During the initial 10 minutes (phase‐1), the wild‐type (WT) subjects contacted the anesthetized conspecifics vigorously regardless of familiarity. During the subsequent 80 minutes (phase‐2), however, they contacted more with familiar than unfamiliar conspecifics. We then applied this test to highly aggressive mice with a hippocampal CA3‐restricted knockout (KO) of brain‐derived neurotrophic factor (BDNF), in which aggression may mask other social behaviors. The KO mice showed less preference for contacting familiar conspecifics than did WT mice during phase‐2 but no differences during phase‐1. Among nonsocial behaviors, WT mice also spent less time eating in the presence of familiar than with unfamiliar conspecifics, which was not seen in KO mice. In addition, KO mice exhibited reduced pain sensitization. Altogether, these findings suggest that CA3‐specific deletion of BDNF results in deficits in circuits that process social cues from familiar conspecifics as well as pain and may underlie empathy‐like behaviors.     

Long‐term monitoring of social behavior in a grouping of six female tigers (Panthera tigris)

Although literature on the reproduction of captive tigers is plentiful, there is little information on other social behaviors, particularly within large social groupings. Here we report on the long‐term monitoring of social behaviors in six female tigers (Panthera tigris). Over a period of 6 years, behavioral data were collected on spraying, vocalizations, non‐contact aggression, and contact aggression during outdoor observations, as well as nearest neighbors in the morning, as a proxy measure of affiliation. Regression analyses showed that non‐contact aggression and vocalizing were increasing, whereas spraying and social proximity were decreasing over the 6 years of the study. Paired t‐tests showed no seasonal differences in aggression, but animals had higher social proximity scores during the mornings of the colder winter months. Correlations showed that spraying was positively related to contact aggression whereas social proximity was negatively correlated with non‐contact aggression. In addition to documenting levels of contact and non‐contact aggression over time, this study showed these behaviors correlated with behaviors that were more easily scored (spraying and social proximity). Behavioral monitoring has played a key role in the management and husbandry of this large social grouping of female tigers. In addition to providing keepers with the opportunity to observe their animals in regularly scheduled sessions, behavioral monitoring has provided baseline information on social relationships in this grouping over time. If future research validates the relationship between aggression and spraying/social proximity, this can be a valuable tool for long‐term monitoring of groups of tigers. Zoo Biol 27:89–99, 2008. © 2007 Wiley‐Liss, Inc.     

Behavioral and hormonal responses to the availability of forage material in Western lowland gorillas (Gorilla gorilla gorilla)

We investigated how forage material affects indicators of welfare in three male Western lowland gorillas (Gorilla gorilla gorilla) at the Detroit Zoo. In addition to their maintenance diet and enrichment foods, the gorillas generally received forage material four times a week. From this baseline, we systematically manipulated how much forage material the group received on a weekly basis, with either daily or bi (twice)‐weekly presentation of browse (mulberry, Morus sp.) or alfalfa hay. We collected behavioral data (60 hr per gorilla) and measured fecal glucocorticoid metabolites (FGM). Mixed models indicated that the presence of forage material significantly increased time feeding (F_2,351 = 9.58, p < 0.001), and decreased rates of noncontact aggression (F_2,351 = 3.69, p = 0.03), and regurgitation and reingestion (F_2,353 = 4.70, p = 0.01). Regurgitation and reingestion were never observed during the condition when forage material was provided daily. When forage material was provided, time spent feeding was similar across gorillas, compared to a disproportionately greater amount of time spent feeding by the dominant individual when forage material was absent. Providing forage material in addition to the regular diet likely created more opportunities for equitable feeding for the subordinate gorillas. FGM concentrations did not vary based on the presence or type of forage material available and, instead, likely reflected group social dynamics. In general, alfalfa and mulberry had similar impacts on behavior, indicating that alfalfa can be an adequate behavioral substitute during times when browse is less readily available for gorillas housed in seasonally variable climates.     

Nutritional composition of the diet of the western gorilla (Gorilla gorilla): Interspecific variation in diet quality

To meet nutritional needs, primates adjust their diets in response to local habitat differences, though whether these dietary modifications translate to changes in dietary nutrient intake is unknown. A previous study of two populations of the mountain gorilla (MG: Gorilla beringei) found no evidence for intraspecific variation in the nutrient composition of their diets, despite ecological and dietary differences between sites. One potential explanation is that nutritional variability in primate diets requires greater ecological divergence than what was captured between MG sites, underpinning environmental differences in the nutrient quality of plant foods. To test whether Gorilla exhibits interspecific variation in dietary composition and nutrient intake, we studied the composition and macronutrients of the western gorilla (WG: Gorilla gorilla) staple diets and compared them with published data from the two MG populations. We recorded feeding time and food intake of four adult female WGs from one habituated group over a period of 11 months (December 2004–October 2005) at the Mondika Research Center, Republic of Congo, allowing for assessment of seasonal patterns of nutrient intake. Staple diets of WGs and MGs diverged in their dietary and macronutrient composition. Compared to MGs, the staple diet of WGs (by intake) contained higher proportions of fruit (43%) and leaf (12%) and a lower proportion of herb (39%), resulting in a higher intake of total nonstructural carbohydrate and fiber and a lower intake of crude protein. Staple gorilla fruits and herbs differed in nutrient quality between sites. Gorillas exhibit nutritional flexibility that reflects ecological variation in the nutrient quality of plant foods. Since dietary quality typically affects rates of growth and reproduction in primates, our results suggest that interspecific differences in nutrient intake and food quality may shape differences in gorilla nutrient balancing and female life history strategies.     

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.     

Behavioral responses of silverback gorillas (Gorilla gorilla gorilla) to videos

This study examined the impact of video presentations on the behavior of 4 silverback, western lowland gorillas (Gorilla gorilla gorilla). On each of 5 occasions, gorillas viewed 6 types of videos (blue screen, humans, an all-male or mixed-sex group engaged in low activity, and an all-male or mixed-sex group engaged in agonistic behavior). The study recorded behavioral responses and watching rates. All gorillas preferred dynamic over static videos; 3 watched videos depicting gorillas significantly more than those depicting humans. Among the gorilla videos, the gorillas clearly preferred watching the mixed-sex group engaged in agonistic behavior; yet, this did not lead to an increase in aggression or behavior indicating agitation. Further, habituation to videos depicting gorillas did not occur. This supports the effectiveness of this form of enrichment, particularly for a nonhuman animal needing to be separated temporarily due to illness, shipment quarantine, social restructuring, or exhibit modification.     

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.     

Effects of combination birth control on estrous behavior in captive western lowland gorillas, Gorilla gorilla gorilla

Combination birth control pills (CBC) are one of the most common birth control methods used for western lowland gorillas (Gorilla gorilla gorilla) housed in zoos. Since zoos are interested in maintaining as many natural behaviors as possible, it is important to know how contraception may affect social and sexual interactions among group members. Although some data are available regarding the influence of the pill on sexual behavior in human females, no data are available on its effects on gorilla estrous behavior. We examined temporal trends of estrous, aggressive, affiliative, and activity budget data in four females on CBC at the Lincoln Park Zoo in Chicago, IL. Behavioral data were collected using point sampling, all-occurrence records, and one-zero sampling. Estrous behavior occurred in less than 1% of observations. Using all-occurrence and one-zero sampling, estrous behavior occurred more frequently in week one of the cycle than any other week. The focal females exhibited affiliative, aggressive, and activity budget data evenly across their cycles. There were also no temporal trends in proximity to the silverback. Females varied by the types of estrous behavior they exhibited. We give a hormonal explanation for the prevalence of estrous behaviors in week one, and recommendations for effective behavioral sampling of gorilla estrous behavior.