Impressive Arboreal Gap-Crossing Behaviors in Wild Bonobos, Pan paniscus

Abstract

Most primates are arboreal, and the current context of habitat fragmentation makes gap-and road-crossing behaviours more and more common. Great apes may try to avoid behaviours such as arboreal leaping because such behaviours are risky given their size. Here, we report impressive gap-crossing by wild bonobos, Pan paniscus, in the Democratic Republic of Congo, induced by human disturbance and habitat fragmentation. We quantify the basic mechanics of leaps and arboreal landing performance in 2 individuals. The bonobos climbed a tree, 15 m high, and performed pronograde leaps between thin flexible branches, to grasp landing branches approximately 4 m further and below their starting point. They reached an instantaneous velocity of about 9 m.s-1. The bonobos used pendular swinging of landing branches to dissipate the kinetic energy built up during falling, requiring a grip force of about 2.5x body weight. Moreover, our results show that bonobos might be able to modulate the drag experienced during falling (up to 20% of body weight) by adjusting their posture. Apparently, bonobos evaluate the structural context to perform the best possible leap and balance the risks against the extra energetic costs involved. Further study of locomotor performance is needed to inform conservation planning, due to the extent of habitat fragmentation due to human activities.

Shape variation in the talus and medial cuneiform of chimpanzees and bonobos

“…Early studies of bonobos at Lomako reported a high frequency of arboreal locomotion in comparison to chimpanzees (Badrian & Badrian, 1977; Doran, 1993a, 1993b; Susman, 1984; Susman et al, 1980). However, this was likely due to poor habituation and a perceived threat from humans as suggested by the high frequency of leaping and diving behaviors (Table 1) (Doran, 1993a; Druelle et al, 2020; Narat et al, 2015; Susman, 1984; Susman et al, 1980). A recent study of fully‐habituated bonobos at LuiKotale found that bonobos are equally, or perhaps even less, arboreal than are eastern and western chimpanzees (Table 2) (Hunt, 2016; Ramos, 2014).…”

<Note>Nkala Forest: Introduction of a forest-savanna mosaic field site of wild bonobos and its future prospects

“…Some research in forest-savanna mosaic environments has been conducted on local ecology (e.g., Serckx et al 2015;Trolliet et al 2016;Pennec et al 2016) and human-bonobo relationships (Inogwabini et al 2013;Narat et al 2015a) in the Mbali area, and also on conservation (Hickey et al 2013) and genetics (Kawamoto et al 2013;Takemoto et al 2017) in Tshuapa-Lomami-Lualaba (TL2) in the eastern end of bonobo's range (Figure 1). However, studies on bonobos' behavior and society in forest-savanna mosaic environments are extremely limited (but see Druelle et al 2020;Narat et al 2015b).…”

African apes and the evolutionary history of orthogrady and bipedalism

“…The idea that bonobos are characterized by more generalized, or at least more versatile, locomotor behavior compared to chimpanzees has received some traction. Bonobos have been observed to engage in more leaping, arboreal palmigrady, and suspensory behaviors than chimpanzees, to be less reliant on tree trunks and more reliant on branches, and paradoxically, inferred as both more terrestrial and more arboreal than chimpanzees (Doran, 1993, 1996; Doran & Hunt, 1994; Druelle et al, 2020; Kano, 1992; Susman, 1984). Horn (1979, p. 367) said of the bonobo that “it would be best described as a generalized, not a specialized, animal,” and also that “the terrestrial and the climbing‐arboreal abilities of the bonobo and the common chimpanzee alike make them well suited to exploiting both terrestrial and arboreal resources.” Susman (1984, p. 389) went so far as to state that “the diverse locomotor repertoire of chimpanzees is probably unequaled among other primates.” As presented in Figure 4, chimpanzees are somewhat generalized in the sense that they engage in a broad array of positional behaviors.…”