The development of feeding behaviour in wild western lowland gorillas (Gorilla gorilla gorilla)

Abstract

Before being weaned, young primates must learn which plant species are suitable to eat, and how to process and combine them to meet their nutritional needs. This study provides a detailed investigation of the development of feeding behaviour in a wild population of western lowland gorillas observed in a bai habitat. The behaviour of 56 known immature individuals aged between 0 and 8 years was recorded at Mbeli Bai, Republic of Congo, using focal, scan and all-occurrence sampling over a period of 16 months. Results indicated that independent feeding skills were acquired by the end of infancy and did not undergo significant change beyond this point. However, suckling continued into the juvenile period, suggesting that some continued investment by the mother was necessary until the strength and skills of immatures developed, perhaps to enable self-sufficiency through periods of succulent fruit (assumed to be the most suitable weaning food) scarcity. This was supported by observations of an increase in feeding-related behaviour with age, particularly during infancy. Additionally, age-related differences in the species and plant parts selected by different age classes, as well as in levels of food processing, were apparent. Play feeding, suggested to be a precursor to independent feeding, was most prevalent in infancy, decreasing as feeding skills developed. Thus, it would appear, given that food transfer also occurs (Nowell & Fletcher, 2006), that feeding skills in western lowland gorillas are learned by a combination of exposure to and manipulation of food items, and probably also through the observation of conspecifics. Observations in a forest habitat are needed to improve our understanding of feeding development in this subspecies.

Human–animal relationships in zoo‐housed orangutans (P. abelii) and gorillas (G. g. gorilla): The effects of familiarity

“…In contrast to bidirectional exchanges, interactions where behaviors are directed from one individual to one or more recipients but a visible response is not produced or cannot be determined are considered unidirectional [Hemelrijk, 1990;Hinde, 1976a,b;Nowell, 2005;Sakamaki, 2009]. To qualify as interactions, unidirectional behaviors must be directed toward recipients who are capable of perceiving or detecting them; for example, visual or audible behaviors are, respectively, directed toward recipients capable of seeing or hearing them.…”

Using behavior to determine immature life‐stages in captive western gorillas

“…Firstly, in agreement with current immature western gorilla life history studies, adolescent males were classed as 6-8 years old [Levrero et al, 2006], and sub-adult males, termed blackbacks, from 8 years until sexually mature at 15 years old [Levrero et al, 2006;Nowell, 2005;Watts & Pusey, 1993]. Secondly, gorillas that continued to suckle from the mother [Nowell & Fletcher, 2007] were reclassified as old infants, due to their continued nutritional dependence on the mother-an observation used extensively in the literature to determine infancy [Pereira & Altmann, 1985].…”

“…However, published research on western gorillas in captivity and in the wild [e.g. Levrero et al, 2006;Lukas et al, 2003a;Maestripieri et al, 2002;Nowell, 2005;Pika et al, 2003;Watts & Pusey, 1993] uses age-based classifications derived from knowledge of mountain gorillas, due to the absence of a classification specifically for western gorillas.…”

“…Infant western gorillas for example have obvious visible white buttock tufts and very dark hair [Breuer et al, 2009]; these somatic features, alongside findings that infants suckle for longer than in mountain gorillas [Nowell & Fletcher, 2007], have led to the proposal that western gorillas have an extended infancy compared to mountain gorillas [Breuer et al, 2009;Nowell, 2005]. This study confirms that western gorilla infants remain behaviorally distinct from juveniles until later than documented in classifications proposed for mountain gorillas [Harcourt et al, 1980;Schaller, 1963;Watts & Pusey, 1993].…”

“…In addition, classifications designed specifically for a species are often adopted in studies of a similar species, without understanding the life history divergence between them. For example, classifications published specifically for mountain gorillas are regularly used for western gorillas (G. gorilla gorilla) in wild and captive studies [Levrero et al, 2006;Lukas et al, 2003b;Nowell, 2005], although recent studies of western gorillas now indicate several environmental and developmental differences between the two species [Doran et al, 2002;Nowell & Fletcher, 2007].…”