Application of insects to wounds of self and others by chimpanzees in the wild.

Self-medication refers to the process by which a host suppresses or prevents the deleterious effects of parasitism and other causes of illness via behavioural means1. It has been observed across multiple animal taxa (e.g. bears, elephants, moths, starlings)2, with many case studies in great apes1,3. Although the majority of studies on self-medication in non-human primates concern the ingestion of plant parts or non-nutritional substances to combat or control intestinal parasites4, more recent examples also report topical applications of leaves or other materials (including arthropods) to skin integuments3. Thus far, however, the application of insects or insect parts to an individual's own wound or the wound of a conspecific has never been reported. Here, we report the first observations of chimpanzees applying insects to their own wounds (n = 19) and to the wounds of conspecifics (n = 3).

Lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on gorillas (Gorilla gorilla gorilla) in the wild.

Intraspecies violence, including lethal interactions, is a relatively common phenomenon in mammals. Contrarily, interspecies violence has mainly been investigated in the context of predation and received most research attention in carnivores. Here, we provide the first information of two lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on another hominid species, western lowland gorillas (Gorilla gorilla gorilla), that occur sympatrically in the Loango National Park in Gabon. In both events, the chimpanzees significantly outnumbered the gorillas and victims were infant gorillas. We discuss these observations in light of the two most widely accepted theoretical explanations for interspecific lethal violence, predation and competition, and combinations of the two-intraguild predation and interspecific killing. Given these events meet conditions proposed to trigger coalitional killing of neighbours in chimpanzees, we also discuss them in light of chimpanzees' intraspecific interactions and territorial nature. Our findings may spur further research into the complexity of interspecies interactions. In addition, they may aid in combining field data from extant models with the Pliocene hominid fossil record to better understand behavioural adaptations and interspecific killing in the hominin lineage.