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Data on the time budgets of mountain gorillas (Gorilla gorilla beringei) were collected during field studies in the Virunga Volcanoes region of Rwanda and Zaire. Focal sampling was used to determine the proportion of time that individuals of different age/sex classes spent in several mutually exclusive activity states. The gorillas spent the majority of daylight hours feeding; most of the rest of the day was devoted to resting, with little time spent moving or engaged in social activity. The time budget varied among the different subhabitats used by the gorillas, and the gorillas satisfied subsistence needs more quickly when in areas where food was more abundant and/or of better nutritional quality. Silverbacks spent more time feeding than all other age/sex classes, but age/sex class differences were not great. All age/sex classes responded to variability in habitat quality in similar fashion. Unlike the case for many other primates, there was no significant seasonal variation in time budgets: There was a direct relationship between group size and time spent feeding, although variation in relation to group size was lower than that in relation to variation in habitat quality. These results are consistent with the relationship of feeding time to body size in primates. They are also consistent with other evidence that social foraging entails a cost to gorilla females, but that this cost is low in comparison to those faced by many other primates. Permanent association with males apparently offers litle ecological disadvantage to females, who are likely to be more than compensated by mutualistic benefits. [ABSTRACT FROM AUTHOR]

This report describes observations on the ontogeny of food choice in mountain gorillas (Gorilla gorilla beringei), made during a 17-month field study of mountain gorilla feeding ecology in the Pare National des Volcans, Rwanda. Data are presented on the feeding behavior of two infants observed from birth to the age of 8 months and on older infants and juveniles. This information is compared with data on the composition and diversity of the diets of young adults and adults in the same social group. Initial feeding by infants is usually synchronized with the mother's behavior: infants ingest the same food, or a different part of the same plant species, currently being eaten by the mother or just eaten by her. This suggests that observational learning is largely responsible for the transmission of food preferences. Most feeding by young infants, whether or not synchronized with the mother's, is on those foods eaten most frequently by adults. Infants also independently sample potential foods, some of which are apparently not consumed by adults. The frequency of sampling declines with age, although even adults occasionally ingest foods not observed to be eaten by other adults. By the age of 3 years, young mountain gorillas have developed the basic dietary patterns of adults, in terms of the number of foods eaten, the proportions in which specific foods are consumed, and diet diversity and equitability. There is a strong possibility that chemical cues influence food choice, but their role remains unclear. [ABSTRACT FROM AUTHOR]

Data are presented here on the feeding ecology of wild mountain gorillas (Gorilla gorilla beringei) which were observed for approximately 2,400 hours over a 17-month period in the Parc National des Volcans, Rwanda. Aspects of the relationship between the composition, diversity, and temporal consistency of the gorillas' diet and spatial and temporal variability in food distribution patterns are described. Mountain gorillas are folivores that show considerable specialization on plant parts, species and families. This pattern is facilitated by the general richness of their habitat. Their environment is heterogeneous, and spatial variability in food distribution is more pronounced than temporal variability. The gorillas rely almost completely on perennially available foliage of herbs and vines. Their diet varies little in association with seasonal factors but varies markedly in space in association with variability in the vegetational composition of the habitat. Individuals in the main study group shared basically similar patterns of food choice. Different groups also shared a similar general pattern, although there were differences in detail that apparently resulted largely from vegetational contrasts between home ranges. The gorillas' behavioral responses to environmental complexity lend general support to recent ideas concerning the evolution of their social system. [ABSTRACT FROM AUTHOR]

Comparative ["evolutionary")] thanatology is devoted to investigating how animals respond to signs of death and dying, in conspecifics and other species. Responses to corpses often involve fear and confusion, and "deceased infant carrying" by females is widespread in nonhuman primates. Such behavior could result from "animacy detection malfunctions" (Gonçalves and Biro in Philos Trans R Soc (B) 373:20170263, 2018): corpses have attributes of animate agents, but-like objects-they do not act, but instead are acted upon by outside forces. Many or most nonhuman primates have core cognitive mechanisms for detecting animacy, but these might not resolve this paradox. Skeletons of conspecifics, seriously injured or ill individuals behaving oddly and not responding as expected to social acts and signals, and corpses, skeletons, and sick or injured individuals belonging to other species could trigger milder animacy detection malfunctions. A central question is whether any nonhuman primates learn from experience that death involves permanent loss of biological functionality and is universal. The relevant literature is mostly anecdotal or devoted to case studies, and this question is open. In response to calls for more information, I describe 25 cases of responses to corpses, skeletons, and mortally injured or ill individuals, both conspecifics and heterospecifics, seen during fieldwork on mountain gorillas (Gorilla beringei beringei) and chimpanzees (Pan troglodytes schweinfurthii). Observations were generally consistent with the animacy detection malfunction hypothesis, although cases of prolonged deceased infant carrying are problematic. Also, one case in gorillas apparently involved sympathetic concern for a dying individual, and sympathetic concern might have occurred in a chimpanzee case.