Biology subjects

Varkevisser, J.

Publications and source records attributed to Varkevisser, J..

3 recordsLinked to original sources

bioRxiv2024

Context-dependent Rhythmicity in Chimpanzee Displays

Rhythm is an important component of human language and music production. Rhythms like isochrony (intervals spaced equally in time), are also present in vocalisations of certain non-human species, including several birds and mammals. This study aimed to identify rhythmic patterns with music-based methods within display behaviour of chimpanzees (Pan troglodytes), humans closest living relatives. Behavioural observations were conducted on individuals from two zoo-housed colonies. We found isochronous rhythms in vocal (e.g. pants, grunts and hoots), as well as in motoric (e.g. swaying and stomping) behavioural sequences. Among individuals, variation was found in the duration between onsets of behavioural elements, resulting in individual-specific tempi. Despite this variation in individual tempi, display sequences were consistently structured with stable, isochronous rhythms. Overall, directed displays, targeted at specific individuals, were less isochronous than undirected displays. The presence of rhythmic patterns across two independent colonies of chimpanzees, suggests that underlying mechanisms for rhythm production may be shared between humans and non-human primates. This shared mechanism indicates that the cognitive requirements for rhythm production potentially preceded human music and language evolution.

animal behavior and cognition↗

bioRxiv2024

The consonance of chords: The effect of subsemitone changes to each of the notes in a trichord on its perceived consonance

Consonance plays a key role in how listeners experience music, but the factors influencing consonance perception remain a topic of discussion, for instance regarding the role of the familiarity of note combinations. Previous empirical studies of consonance have used common, familiar chords, making it harder to separate the effect of acoustic features from familiarity. Here we explored consonance perception in an unfamiliar, non-standardly tuned 0-5-10 trichord. A test was conducted in which 100 musicians and 100 nonmusicians compared the consonance of an original, non-standard, 0-5-10 chord and an adapted version, in which the lowest, middle or upper note was raised or lowered with 25 or 50 cents. According to a model based on continuous acoustic features, any adaptation to a 0-5-10 chord should yield a comparable decrease in consonance. We indeed found a general consonance decrease, but this was stronger for adaptations enlarging the distance between the lowest and the upper note, i.e. lowering the lowest or raising the highest note, than for other adaptations. These results deviate from the models predictions and from patterns observed in standard, more familiar chords. Future research should examine the generalizability of these findings to other chords than the 0-5-10 trichord.

animal behavior and cognition↗

bioRxiv2024

Adult male Lar gibbon sings the female great-call: A case study of inter-sex song production in a non-human primate

Gibbons are known as one of the most vocal non-human primates. They vocally advertise and reinforce their pair-bonds by singing complex duets, in which both the male and female perform a predetermined sex-specific set of song phrases, including the loud and elongated great-calls. Only females and sub-adult male gibbons have been previously observed performing great-calls. Once a male gibbon matures, he normally stops great-call production completely but continues singing other and less high-pitched song phrases. This case study describes a fully adult, castrated male lar gibbon (Hylobates lar, 32 years old, zoo-housed) who performs both male phrases of the duet, including the female great-call. The male regularly produced great-calls despite being in a, relatively weak, pair bond with a female conspecific. His great-calls adhered to the general structure of typical female great-calls but were shorter and had a lower maximum frequency. Notably, he produced these great-calls predominantly when the female was absent, especially when she was in their inside enclosure whilst he was outside. Behavioural observations indicate that the occurrence of great-calls by the male cannot be predicted based on pre-song behaviour or his interaction with the female. The recurrence of sub-adult singing behaviour in a fully grown adult is most likely due to his reduced testosterone levels. This study sheds light on the intricate dynamics of duetting and the unique occurrence of cross-sex song production in gibbons, emphasizing the complexity of pair-bond communication in this species.

animal behavior and cognition↗