Diet of chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda, 1. diet composition and diversity

Abstract

Chimpanzees (Pan troglodytes) are ecologically flexible omnivores with broad diets comprising many plant and animal foods, although they mostly eat fruit (including figs). Like other ecologically flexible nonhuman primates (e.g., baboons, Papio spp.) with broad diets, their diets vary across habitats. Much data on diets come from short studies that may not capture the range of variation, however, and data are scant on variation within habitats and populations. We present data on diet composition and diversity for chimpanzees at Ngogo, in Kibale National Park, Uganda, collected over a 15-year period, with a focus on the plant components of the diet. We compare Ngogo data to those on chimpanzees at the nearby Kibale site of Kanyawara, on other chimpanzee populations, and on some other frugivorous-omnivorous primates. Results support the argument that chimpanzees are ripe fruit specialists: Ngogo chimpanzees ate a broad, mostly fruit-based diet, feeding time devoted to fruit varied positively with fruit availability, and diet diversity varied inversely with fruit availability. Comparison of Ngogo and Kanyawara shows much similarity, but also pronounced within-population dietary variation. Chimpanzees fed much more on leaves, and much less on pith and stems, at Ngogo. Figs accounted for somewhat less feeding time at Ngogo, but those of Ficus mucuso were quantitatively the most important food. This species is essentially absent at Kanayawara; its abundance and high productivity at Ngogo, along with much higher abundance of several other important food species, help explain why chimpanzee community size and population density are over three times higher at Ngogo. High inter-annual variation at Ngogo highlights the value of long-term data for documenting the extent of ecological variation among chimpanzee populations and understanding how such variation might affect population biology and social dynamics.

Hunting and Prey Switching by Chimpanzees (Pan troglodytes schweinfurthii) at Ngogo

“…We did not find evidence for a direct effect of variation male party size on hunting rates; instead, our results were consistent with a direct effect of fruit availability; that is, chimpanzees are more likely to hunt when they can easily meet energy requirements by eating fruit (Gilby and Wrangham 2007;Watts and Mitani 2002a, b). Further support for the risk prone foraging hypothesis comes from the fact that the 2002 hunting peak included two prolonged hunting "binges," each of which coincided with one of two major fruiting events that year by U. congensis (the top nonfig fruit in the diet at Ngogo; Watts et al 2012); the first of these events also overlapped a major fruit crop by P. microcarpa. Other major fruiting events have led to similar, if more modest, binges.…”

“…Also, redtails and magabeys feed heavily on some fruit species important for chimpanzees. We used least squares regression and a general linear model to examine relationships of monthly encounter and hunting rates to the proportion of monthly feeding time devoted to those 15 fruit species (including figs) that each contributed >1 % of feeding time on a long-term basis (Watts et al 2012) and to the mean monthly value for the maximum number of adult males that associated per day. We subjected feeding proportions to arcsin square root transformation; resulting values were normally distributed (χ 2 =2.52, d.f.…”

“…As for the encounter rate data, sampling was unevenly distributed among months; e.g., one or both of us was at Ngogo from June through August in every year except 1998, but December was sampled in only 4 yearr. This should not introduce substantial bias, because no seasonal effects on hunting are evident at Ngogo (Mitani and Watts 2005) and seasonality in fruit production and diet is limited (Watts et al 2012). However, the sampling gaps preclude use of time series analysis to investigate possible lag effects due to variation in red colobus predation intensity.…”

“…Chimpanzees are mostly secondary consumers, not obligate carnivores, and plant parts, especially fruit and figs, comprise most of their diet (Watts et al 2012). Variation in populations of their vertebrate prey might influence the frequency with which chimpanzees hunt, but probably does not influence chimpanzee demography and population density.…”

Do chimpanzees like alcohol?

“…Chimpanzees build fission-fusion societies whereby the main group occasionally splits up into smaller feeding parties and later fuses again (Boesch 2012). They are omnivores preferentially feeding on fruit for more than 75% of their total feeding time in some habitats (Watts et al 2012) and their cultures in the wild are famous for sophisticated tools use that includes poking sticks (Whiten et al 1999).…”