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Abstract ObjectivesWeaning is a key life history milestone for mammals that represents both the end of nutritional investment from the perspective of mothers and the start of complete nutritional independence for the infants. The age at weaning may vary depending on ecological, social, and demographic factors experienced by the mother and infant. Bwindi mountain gorillas live in different environmental conditions and have longer interbirth intervals than their counterparts in the Virunga Volcanoes, yet other life history characteristics of this population remain less well known. We use long‐term data from Bwindi Impenetrable National Park, Uganda to examine factors related to weaning age. Materials and methodsWe analyzed data on infants born in four mountain gorilla groups in Bwindi to quantify their age of weaning (defined as last nipple contact) and to test if the sex of offspring, parity, and dominance rank of mother influences age of weaning. We also compared the age at weaning and time to conception after resumption of mating in Bwindi and Virunga gorillas. ResultsBwindi gorillas were weaned at an average age of 57.5 months. No difference was found between age of weaning for primiparous and multiparous mothers, nor did maternal dominance rank influence age of weaning, but sons were weaned at a later age than daughters. The majority of Bwindi mothers were still suckling when they resumed mating and mothers generally conceived before they weaned their previous offspring. The age of weaning was significantly later in Bwindi than in Virunga gorillas. After mothers resumed mating, the time to conceiving the next offspring was not significantly longer for Bwindi females than Virungas females (6 vs. 4 months). DiscussionLater weaning age for sons than daughters is similar to findings of other studies of great apes. Bwindi mountain gorillas are weaned at approximately the same age as western gorillas and chimpanzees, which is more than a year later than Virunga mountain gorillas. The results of this study suggest that variation in ecological conditions of populations living in close geographic proximity can result in variation in life history patterns, which has implications for understanding the evolution of the unique life history patterns of humans.
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Fruit‐feeding and activity patterns of mountain gorillas ( Gorilla beringei beringei ) in Bwindi Impenetrable National Park, Uganda
Abstract ObjectivesAvailability of fruit is an important factor influencing variation in great ape foraging strategies and activity patterns. This study aims to quantify how frugivory influences activity budgets across age‐sex classes of mountain gorillas in Bwindi Impenetrable National Park, Uganda. Materials and methodsDaily proportions of fruit‐feeding and activity budgets were calculated using 6 years of observational data on four habituated groups. We fitted generalized linear mixed models to test for age‐sex differences in the amount of fruit‐feeding, and to test whether these factors influence the proportion of time spent feeding, resting, and traveling. ResultsBwindi mountain gorillas spent on average 15% of feeding time consuming fruit, with monthly variation ranging from 0 to 70%. Greater amounts of fruit‐feeding were associated with more time feeding and traveling, and less time resting. Immatures tended to spend more feeding time on fruit than adults, but less overall time feeding and more time traveling. There were no significant differences in the amount of fruit‐feeding and overall feeding time between adult females and silverback males, despite differences in body size. DiscussionThis study confirms that gorillas are frugivorous, and only the Virunga mountain gorilla population can be characterized as highly folivorous. Along with other frugivorous great apes, Bwindi mountain gorillas alter their activity patterns in response to varying amounts of fruit in their diet. A better understanding of how variable ecological conditions can drive diversity even within a subspecies has important implications for understanding relationships between ecology, body size, and foraging strategies in great apes.
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- Award ID(s):
- 1753963
- PAR ID:
- 10456776
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Physical Anthropology
- Volume:
- 173
- Issue:
- 1
- ISSN:
- 0002-9483
- Format(s):
- Medium: X Size: p. 3-20
- Size(s):
- p. 3-20
- Sponsoring Org:
- National Science Foundation
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