Do Chimpanzee Nests Serve an Anti‐Predatory Function?

Abstract

Sleep is a vulnerable state for animals as it compromises the ability to detect predators. The evolution of shelter construction in the great apes may have been a solution to the trade-off between restorative sleep and predation-risk, which allowed a large bodied ape to sleep recumbent in a safe, comfortable spot. In this article we review the evidence of predator pressure on great apes and specifically investigate the potential influence of predation-risk on chimpanzee nesting behavior by comparing nests between chimpanzees living in a habitat of several potential predators (Issa, Ugalla, Tanzania) and a habitat relatively devoid of predators (Fongoli, Senegal). Chimpanzees in Issa did not nest more frequently in forest vegetation than chimpanzees in Fongoli although forest vegetation is expected to provide greater opportunity for escape from terrestrial predators. Nor do chimpanzees in Issa nest in larger groups or aggregate together more than Fongoli chimpanzees, as would be expected if larger groups provide protection from or greater detection of predators. Nests in Issa also did not appear to provide greater opportunities for escape than nests in Fongoli. Chimpanzees in Issa nested more frequently within the same tree as other community members, which may indicate that these chimpanzees nest in greater proximity than chimpanzees in Fongoli. Finally, Issa chimpanzees built their nests proportionately higher and more peripherally within trees. The selection of high and peripheral nesting locations within trees may make Issa chimpanzees inaccessible to potential predators. Many factors influence nest site selection in chimpanzees, of which danger from terrestrial predators is likely to be one.

Wild chimpanzees plan their breakfast time, type, and location

“…2) (18% of all departures were before sunrise), when navigation is difficult and predation risk is greatest, begs the question as to why they did not simply sleep closer to or inside the breakfast trees. Disturbed sleep by nocturnal frugivores or insects and a strong preference for particular nest locations, influenced by tree species (28,37), particular leaf characteristics such as softness or insect repellent properties (38,39), tree crown morphological features (38,40), vegetation and landscape characteristics (40), and predation risk (38,41), all explain why they did not (see Fig. S6 and Supporting Information for the females' preference scores).…”

Endangered West African Chimpanzees Pan troglodytes verus (Schwarz, 1934) (Primates: Hominidae) in Senegal prefer Pterocarpus erinaceus, a threatened tree species, to build their nests: implications for their conservation

“…1), in West Africa. See Pruetz et al (2002Pruetz et al ( , 2008 and Stewart & Pruetz (2013) for detailed descriptions of the habitat vegetation types. We surveyed the entire region for chimpanzee habitats based on the presence of their nests.…”

“…Baldwin et al (1981) collected information on nest heights, nest grouping, the number of nests per nest tree, the minimum distance between nests and nest tree trunk diameters in the Niokolo Koba National Park. At Fongoli, approximately 50km southeast of Niokolo Koba National Park in southeastern Senegal, Stewart et al (2007) studied the comfort of chimpanzee nests on the basis of their physical features; Stewart & Pruetz (2013) describe the anti-predator function of the nest. Pruetz et al (2008) studied chimpanzees around Fongoli in comparison to those in the protected Niokolo Koba National Park to assess the anti-predator role of chimpanzee arboreal nest building behaviour, while also carefully detailing habitat structure and arboreal nest heights.…”

Ground Night Nesting in Chimpanzees: New Insights from Central Chimpanzees (Pan troglodytes troglodytes) in South-East Cameroon

“…Other studies have failed to support the antipredation hypothesis (gorillas in Mondika, Central African Republic, and Lopé [Mehlman and Doran, 2002]; chimpanzees [Koops et al, 2012a;Stewart and Pruetz, 2013]), although they do not exclude the possibility that arboreal nests functioned (partly) as an antipredator strategy in the past. Furthermore, additional factors likely contribute to nest site location [Brownlow et al, 2001;Pruetz et al, 2008;Koops et al, 2012a;Stewart and Pruetz, 2013], and to the need for construction of a nest [Pruetz et al, 2008;Stewart, 2011a].…”

“…As tree nest building is suggested to increase the safety of sleeping apes [Baldwin et al, 1981], predation is likely to influence nesting patterns [Ogawa et al, 2007], for example with an increase in nesting height [Pruetz et al, 2008;Stewart and Pruetz, 2013]. Gorillas commonly build nests on the ground, and their sexual dimorphism and the increased tendency for immature gorillas and adult females to nest in trees suggests a protective role of males sleeping on the ground [Yamagiwa, 2001].…”