05:25: Mélodie Kreyer (MK), Giulia Rossi (GR), and Nicolas Corredor-Ospina (NC) start observations at a nest site of the WBp community. The night-nest party is composed of 19 mature individuals, four males (one adolescent; three adult); and 15 females (five nulliparous; nine with offspring; one old) (see Fig. 1 for a schematic depiction of the day).
06:10: Individuals descend to the ground and split into several smaller parties that move in different directions:
Party #1 followed by NC: consisting of one adult male and three females (two nulliparous; one with offspring)
06:44: After splitting from the rest of the nest group, party #1 travels north. Bonobos climb a tree and feed on pods of Scorodophloeus zenkeri for 30 min before descending and continuing north.
07:48: After hearing distance vocalizations at around 07:42, NC catches up with the party. Bonobos are up in the trees giving agonistic calls (type contest hoots, screams and whistle-barks sensu De Waal (1988)). While approaching the group, NC notices a group of roughly ten red river hogs foraging on the shrub Cissus dinklagei, and mistakenly attributes the bonobos’ calls as reaction to the river hogs. However, in response to an unidentified roaring from the canopy, the hogs flee (07:53), while the bonobos continue emitting agonistic calls. With this roaring later attributed to a leopard, bonobos were estimated to be in proximity to the leopard since 07:40.
Party #2 followed by GR: consisting of two adult females with offspring.
06:15: After splitting from the rest of the nest group, party #2 travels west towards the Badzungu river, where they are lost from view just before crossing the river (06:19). GR returns and joins MK with party #3 (06:30).
Party #3 followed by MK and GR: consisting of one adult male and six females (two nulliparous; three with offspring; one old)
06:20: After splitting from the rest of the nest group, party #3 moves north-east and feeds on Landolphia forestiana for less than 10 min. After a brief stop during which the adult male fed on Anonidium mannii, the group travelled about 2 km north-east and entered another feeding tree (Drypetes sp.) at 07:12, where they fed until 07:39.
07:40: MK and GR hear distance calls from party #1, which cause some members of party #3 to appear nervous and agitated. All individuals descend rapidly and start rushing in the direction of the vocalizations of party #1. GR and MK follow the direction of the distance calls, briefly losing sight of party #3.
08:00: NC observes fusion of party #3 with party #1, resulting in party #4. MK and GR arrive (08:05). Individuals of party #1 did not change their behaviour after fusion with party #3.
Party #4 followed by MK, GR, and NC: consisting of two adult males and nine females (four nulliparous; four with offspring; one old).
08:05: Focusing on the arboreal source of roaring vocalizations, observers locate a leopard, surrounded by party #4 members in neighbouring trees. The leopard’s body is hidden by what looks like the remains of a bonobo nest, with only the tail visible from the ground. The nest is on branches about 10–12 m high, in the middle of a Dialium sp. tree.
08:06: Emil, an adult male bonobo, is in a nearby tree, close (4–5 m) to the leopard and sporadically shaking branches. The rest of the party is in the canopy, surrounding the leopard’s tree from a distance of 10–20 m. Some of the adults continue vocalizing loudly towards the leopard. A few feed on Dialium leaves, but in general all look highly alert.
08:19: The leopard appears nervous, frantically swaying its tail and roaring loudly in response to bonobos’ intermittent agonistic vocalizations and displays. However, the leopard does not move from his arboreal spot for over an hour.
09:13: Emil descends to the ground, followed by other individuals. Most individuals, including two adult females and infants inspect the ground and smell what seems to be leopard pee. The nulliparous female Flora remains in the leopard’s tree and approaches “his” nest.
09:19: Flora, about 5 m away from the nest is threatened away by the leopard. This is the first aggression towards a bonobo. The other individuals respond by hitting tree trunks with hand and feet and by vocalizing loudly. Emil and others climb up trees again.
09:20: Jack, an adult male, climbs the leopard’s Dialium tree, stopping to smell the trunk where claw marks are visible, and the surrounding vegetation. An unidentified individual climbs the tree and approaches to 5–7 m from the nest. At this point the leopard jumps from the nest and chases the approaching bonobo away. The leopard stops at the main trunk, looks at the observing humans, and returns to the nest. Bonobos continue shaking branches, hitting trunks, and screaming at the leopard. At least three nulliparous, one old, and two adult females with their offspring remain on the ground while both adult males, the other nulliparous and two adult females with their offspring are up in the trees. The leopard roars and moves towards any bonobo that approaches to within 5 m. Emil, Jack and Flora are most active in harassing the leopard from near this distance. Most infants remain close to their mothers apart from one male who actively inspects the ground and returns to his mother at each new sound from above. Whenever the leopard leaves the nest and roars to try to displace the arboreal harassers, terrestrial bonobos respond by jumping back into trees and joining in the chorus of screams and barks. All party members give agonistic vocalizations; three of them stay close without actively harassing the leopard, while three (Emil, Jack, Flora) get closest to it. Others, such as Paula, a high-ranking female, stays in the leopard’s tree and feeds on Dialium leaves.
09:40: A total of nine of the 11 mature bonobos of party #4 start slowly and silently to withdraw from the area. Two, Flora and Jack, remain in the tree and continue approaching the leopard in its nest.
09:43: Jack moves nearer, and displaces the leopard, which roars and moves towards Jack before jumping to a higher spot. Immediately, Jack inspects the inside of the empty nest, smelling it. Jack then descends to the ground, leaving Flora alone in the tree.
09:45: Flora continues harassing the leopard, until it jumps and chases her away. In response, bonobos again climb nearby trees, scream and shake branches. This time the leopard retreats to the Dialium’s tree highest point, when Jack again ascends the tree and returns to the nest, which he sniffs. Flora again approaches the leopard to within 4–5 m, hitting her support-branch with her feet and hands, and flailing an arm towards the leopard. The leopard shows its teeth in a clear threat (Video 1).
09:49: A female with offspring joins the party.
10:00: All bonobos descend and walk around 100 m to feed on Cissus dinklagei. Researchers follow the bonobos, losing sight of the leopard, still in the tree.
10:25: The two males, and six females (three nulliparous; three adult) descend from their arboreal food patch and return to the Dialium tree where the leopard was earlier; the other bonobos continue feeding. The returning individuals climb up, sniff the vegetation in and around the nest, and leave 5 min later. The leopard was not seen or heard again.
10:50: Bonobos leave the area and walk rapidly back south-west, neither foraging nor engaging in any sort social interaction. They cross the Badzungu river and move into the most western part of their home range. They travel almost continuously until party #4 fuses with other members (party #5) of the community at 12:00–13:20, feeding on C. dinklagei fruits, about 4 km in a beeline from the location of the leopard encounter. During the rest of the day the fused party #6 (containing four males and 16 females), continues travelling, feeding, and resting, until they build their night nests starting at 17:42 (Fig. 1).
The leopard was a male, probably not fully grown. No injuries or signs of disability were noted. There was no physical contact between bonobos and the leopard. Immature bonobos remained in physical contact with their mothers.