Age related decline in female lar gibbon great call performance suggests that call features correlate with physical condition

Abstract

BackgroundWhite-handed gibbons (Hylobates lar) are small Asian apes known for living in stable territories and producing loud, elaborate vocalizations (songs), often in well-coordinated male/female duets. The female great call, the most conspicuous phrase of the repertoire, has been hypothesized to function in intra-sexual territorial defense. We therefore predicted that characteristics of the great call would correlate with a caller’s physical condition, and thus might honestly reflect resource holding potential (RHP). Because measurement of RHP is virtually impossible for wild animals, we used age as a proxy, hypothesizing that great call climaxes are difficult to produce and maintain over time, and that older adults will therefore perform lower quality great calls than young adults. To test this we analyzed the great call climaxes of 15 wild lar gibbon females at Khao Yai National Park, Thailand and 2 captive females at Leo Conservation Center, Greenwich, CT.ResultsFindings show that call climaxes correlate with female age, as young animals (n = 8, mean age: 12.9 years) produced climaxes with a higher frequency range (delta F0), maximum F0 frequency and duty cycle than old animals (n = 9, mean age: 29.6 years). A permuted discriminant function analysis also correctly classified calls by age group. During long song bouts the maximum F0 frequency of great call climaxes’ also decreased. Additional data support the hypothesis that short high notes, associated with rapid inhalation as an individual catches its breath, reflect increased caller effort. Older females produced more high notes than younger females, but the difference only approached statistical significance, suggesting that calling effort may be similar across different ages. Finally, for the first time in this species, we measured peak intensity of calls in captive females. They were capable of producing climaxes in excess of 100 dB at close range (2.7 m).ConclusionsAge and within-bout differences in the lar gibbon great call climax suggest that call features correlate with physical condition and thus the call may have evolved as an honest signal in the context of intra-sexual territorial defense and possibly also in male mate choice via sexual selection, although further testing of these hypotheses is necessary.

An analysis of white‐handed gibbon male song reveals speech‐like phrases

“…Similarly, we have described an increase in maximum coda frequency as vocal duets progress. Other findings, also in white‐handed gibbons, show that higher frequency notes associate with both androgen levels (Barelli et al, ), and potentially with a caller's physical condition (Terleph et al, ).…”

“…Recordings were 24 bit, with a 48 kHz sample rate. We defined codas as the male song unit that immediately follows a mate's complete great call (great calls that reach climax, see Terleph et al, ), and based on the timing of typical onsets (Terleph et al, ), that started within 5 sec of the great call's termination. We defined the last phrase of each coda as that followed by ≥500 ms of silence, as less stereotyped male singing typically follows a coda after a pause of at least 500 ms. We converted all recordings into spectrograms (Window type: Hann, FFT size: 1124 Hz, frame overlap: 50%), using Raven Pro 1.5 Sound Analysis Software (Cornell Lab of Ornithology Bioacoustics Research Program, Ithaca, New York), and manually made measurements from the spectrograms.…”

Gibbons aren’t singing in the rain: presence and amount of rainfall influences ape calling behavior in Sabah, Malaysia

“…Previous reports of soloing by paired versus floating males indicate that performances by solitary males are 'indistinguishable' from those of paired males 18 , which means that we have no way to know whether the solos we documented in our dataset paired or floating males mated or solitary males. Although the function of gibbon solos and duets remains a topic of debate 44 , if the male solo functions to advertise resource holding potential 24 , as an assessment signal 30 or for mate attraction 45 , it is possible that mated or unmated males are differentially impacted by environmental conditions. Whereas if solos simply serve a function to provide www.nature.com/scientificreports www.nature.com/scientificreports/ information to conspecifics regarding individual identify and location 44,46 , we would not expect to see differences between paired versus floating males.…”

Facial expressions and pair bonds in hylobatids

“…Contrary to our understanding, it has been argued that visual‐gestural communication in hylobatids should be relatively unimportant since hylobatids live in dense, low‐visibility environments and would therefore benefit more from relying on vocal communication (Maestripieri, ; Liebal et al, ). Such view is supported by the widely recognized, extraordinary vocal abilities of all hylobatid species (Clarke, Reichard, & Zuberbühler, ; Geissmann, ; Haimoff, ; Keith, Waller, & Geissmann, ; Terleph, Malaivijitnond, & Reichard, ; Thin, Hallam, Roos, & Hammerschmidt, ). However, communication modalities are not mutually exclusive, and vocal and visual systems may have evolved independently for different reasons.…”