Wild chimpanzee offspring exhibit adult‐like foraging patterns around the age of weaning

Abstract

Objectives The prolonged juvenile period exhibited by primates is an evolutionary conundrum. Here we examine wild chimpanzee feeding development in the context of two hypotheses regarding prolonged development in primates: the needing‐to‐learn hypothesis and the expensive brain hypothesis. Material and Methods We studied wild chimpanzee (Pan troglodytes schweinfurthii) offspring at Gombe National Park, Tanzania. We analyzed 41 years of observational behavioral data collected between 1975 and 2016 from 81 offspring. We characterized feeding development in the first 10 years of life via four different measures: (1) proportion of observation time spent feeding; (2) diet composition; (3) diet breadth; and (4) diet maturity as measured by similarity to maternal diet. We used mixed effects models to examine changes with age and by sex, while controlling for season. Results Feeding time, diet breadth, and diet maturity exhibited the most substantial increases with age in the first 6 years, with no significant change thereafter. Males and females showed different patterns of change in diet breadth by age, but did not differ by age 10. Diet composition did not change significantly with age and did not differ by sex. Discussion We found that chimpanzee offspring attained adult‐like feeding behaviors between 4 and 6 years of age, concomitant with the completion of weaning. Thus, our data do not support the needing‐to‐learn feeding skills hypothesis of a prolonged juvenile period, but additional data are needed to evaluate how and when adolescent chimpanzees are able to make foraging decisions independent of their mothers. Existing data on growth provides support for the expensive brain hypothesis, however, these hypotheses are not necessarily mutually exclusive. As more studies across taxa accumulate sufficient datasets on a range of developmental metrics, we will be able to achieve a more robust understanding of prolonged development in primates.

Drinking frequency in wild lactating chimpanzees (Pan troglodytes schweinfurthii) and their offspring

“…High‐ranking female chimpanzees are more likely to wean their infants earlier than low‐ranking females (Lonsdorf et al, 2020), but evidence for shorter IBIs for high‐ranking mothers is mixed (Jones et al, 2010; Stanton et al, 2017). Recent work has found chimpanzee infants obtain adult‐like feeding patterns between 4 and 6 years of age (Bray et al, 2018; Lonsdorf et al, 2021), however, variation in feeding development between offspring based on maternal rank has not been investigated. If the offspring of high‐ranking females develop and reach adult‐like diets faster, late lactation may present less of a hydration burden as compared to low‐ranking females with slower developing offspring.…”

“…During early lactation (0–1.5 years), offspring are mostly dependent on mothers for nutrition and are in close proximity to their mothers (Goodall, 1986; Lonsdorf et al, 2014), which may impact how much milk they are consuming. Offspring in middle lactation (1.5–3 years of age) increasingly incorporate solid food into their diets, but still depend on supplemental milk (Bray et al, 2018; Lonsdorf et al, 2021). Offspring in late lactation (3–4.5 years of age) are nearing weaned age, and as such might be less dependent on milk for hydration.…”

“…Offspring in middle lactation (1.5-3 years of age) increasingly incorporate solid food into their diets, but still depend on supplemental milk (Bray et al, 2018;Lonsdorf et al, 2021). Offspring in late lactation (3-4.5 years of age) are nearing weaned age, and as such might be less dependent on milk for hydration.…”

“…Additionally, maternal dominance rank can impact weaning patterns, with low‐ranking mothers less likely to wean their offspring early as compared to high‐ranking mothers (Lonsdorf et al, 2020). Research has demonstrated that immatures develop adult‐like diet breadth and composition by juvenility (Bray et al, 2018; Lonsdorf et al, 2021). Acquisition of adult‐like drinking patterns, as well as obtaining enough water from their diet may also be an important transition after weaning.…”

Protracted development of stick tool use skills extends into adulthood in wild western chimpanzees

“…Several studies demonstrate that social facilitation influences chimpanzee learning of object manipulation tasks in captivity [99,100]. In the wild, a prolonged developmental period and maternal dependency are suggested to facilitate the gradual learning of complex foraging tasks ( [42,55,57,101,102,103]; although see [104,105]). Anecdotal observations demonstrate that chimpanzees continue to closely observe others (peering) after their juvenile years, especially when unusual objects are being manipulated or unusual actions are performed with them [106][107][108].…”