Acoustic features contributing to the individuality of wild agile gibbon (Hylobates agilis agilis) songs

Abstract

We examined acoustic individuality in wild agile gibbon Hylobates agilis agilis and determined the acoustic variables that contribute to individual discrimination using multivariate analyses. We recorded 125 female-specific songs (great calls) from six groups in west Sumatra and measured 58 acoustic variables for each great call. We performed principal component analysis to summarize the 58 variables into six acoustic principal components (PCs). Generally, each PC corresponded to a part of the great call. Significant individual differences were found across six individual gibbons in each of the six PCs. Moreover, strong acoustic individuality was found in the introductory and climax parts of the great call. In contrast, the terminal part contributed little to individual identification. Discriminant analysis showed that these PCs contributed to individual discrimination with high repeatability. Although we cannot conclude that agile gibbon use these acoustic components for individual discrimination, they are potential candidates for individual recognition.

Macrogeographical variability in the great call of Hylobates agilis: assessing the applicability of vocal analysis in studies of fine‐scale taxonomy of gibbons

“…Dallmann & Geissmann, 2001;Haimoff & Gittins, 1985;Oyakawa et al, 2007]. The onset of the great calls was easily identifiable, and we considered all notes with a duration >0.5 sec to be a part of the great call.…”

“…Great calls are highly contextual, and it is clear that they consist of a few types (or phases) of notes defined by their pattern of frequency modulation. We defined three phases (introductory, climax and terminal, modified from previous studies) to facilitate comparison between great calls across individuals and samples [Haimoff, 1984;Dallmann & Geissmann, 2001;Oyakawa et al, 2007]. The following definitions were used to distinguish elements and phases within the great call:…”

Population Differences and Acoustic Stability in Male Songs of Wild Western Black Crested Gibbons (Nomascus concolor) in Mt. Wuliang, Yunnan

“…A stepwise discriminant function analysis (DFA) was used to identify population differences and acoustic stability [Butynski et al, 1992;Jones et al, 1993;Konrad and Geissmann, 2006;Oyakawa et al, 2007]. For the stepwise procedure, we determined Wilks' lambda as the criterion for variable selection.…”

“…If gibbon song functions as a means of intragroup and intergroup communication, selection may have favoured individuality of songs [Haimoff and Gittins, 1985]. Acoustic individuality has, indeed, been reported in several species of gibbons ( Hylobates agilis [Haimoff and Gittins, 1985;Oyakawa et al, 2007]; H. klossii [Haimoff and Tilson, 1985]; H. moloch [Dallmann and Geissmann, 2001]), including the western black crested gibbon [Sun et al, 2011].…”

“…Call individuality in the squirrel monkey ( Saimiri sciureus [Symmes et al, 1979]), blue monkey ( Cercopithecus mitis stuhlmanni [Butynski et al, 1992]) and common marmoset ( Callithrix jacchus [Jones et al, 1993]) maintains acoustic consistency over several years, enough to identify individuals. Research on acoustic individuality in gibbons has, to date, been based on recordings made in only a short time period, and it has not, therefore, been possible to test song stability [Haimoff and Gittins, 1985;Haimoff and Tilson, 1985;Dallmann and Geissmann, 2001;Oyakawa et al, 2007;Sun et al, 2011].…”