Table 1.
Criteria used for identifying intentional production of communicative signals, as outlined in the study of great ape gestures [19]–[36].
Figure 1.
Example spectrographic representations of chimpanzee alarm calls.
This Figure illustrates (A) Soft Huu (SH), (B) Alarm Huu (AH) and (C) Waa Bark (WB) vocalizations. The x-axis represents time in seconds, the y-axis frequency (KHz). The darkness of the image represents the amount of acoustic energy present, or the amplitude of the sound. SH are short (∼100 ms), tonal, and low pitched (<500 Hz), and usually have a low amplitude and little frequency modulation (Audio S1). These soft calls are unlikely to be heard by individuals further than 50 m from the call producer and are comparable with the ‘huu vocalizations’ described by Goodall [11] as well as the alert hoos reported in Crockford et al. [10]. AH are longer, louder, higher pitched, and with more frequency modulation compared to soft huus (Audio S2). These tonal calls are comparable with the ‘alarm calls’ described in Slocombe and Zuberbühler [72]. WB are loud, abrupt sounds with a noisy spectral quality (Audio S3). They typically start with a low frequency ‘w’ introduction at call onset, followed by considerable frequency modulation in the subsequent higher frequency element that can sound like an ‘aa’ ‘aow’ or ‘aoo’ sound to the human ear.
Table 2.
Behaviours continuously coded from when the snake was revealed to the end of the trial when the focal individual had moved further than 10
Figure 2.
Diagram of the experimental set up.
The snake image represents the location of the python model, concealed by leaves not depicted. Observers are depicted by grey asterisks and their main roles defined. Observer 4 was optional in the set-up. The chimpanzee image depicts the focal chimpanzee, who could be accompanied by other group members depending on the experimental condition.
Figure 3.
Percentage of cases (raw data) where a look to another chimpanzee was present/absent in the 5 sec before a new call bout as a function of the type of call then given.