DOI: 10.5061/dryad.dz08kprw6
title: Adherence to Menzerath’s Law is the exception (not the rule) in three duetting primate species

description: Across diverse systems including language, music, and genomes, there is a
 tendency for longer sequences to contain shorter constituents; this
 phenomenon is known as Menzerath’s law. Whether Menzerath’s law is a
 universal in biological systems, is the result of compression (wherein
 shortest possible strings represent the maximum amount of information) or
 emerges from an inevitable relationship between sequence and constituent
 length remains a topic of debate. In nonhuman primates, the vocalizations
 of geladas, male gibbons, and chimpanzees exhibit patterns consistent with
 Menzerath’s law. Here we utilize existing datasets of three duetting
 primate species (tarsiers, titi monkeys, and gibbons) to examine the
 widescale applicability of Menzerath’s law. Primate duets provide a useful
 comparative model to test for the broad-scale applicability of Menzerath’s
 law, as they evolved independently under presumably similar selection
 pressures and are emitted under the same context(s) across taxa. Only four
 out of the eight call types we examined were consistent with Menzerath’s
 law. Two of these call types exhibited a negative relationship between
 position of the note in the call and note duration, indicating that
 adherence to Menzerath’s law in these call types may be related to
 breathing constraints. Exceptions to Menzerath’s law occur when notes are
 relatively homogenous, or when species-specific call structure leads to a
 deterministic decrease in note duration. We show that adherence to
 Menzerath’s law is the exception rather than the rule in duetting
 primates. It is possible that selection pressures for efficient long-range
 communication of duets was stronger than that of compression. Future
 studies investigating adherence to Menzerath’s law across the vocal
 repertoires of these species will help us better elucidate the pressures
 that shape both short- and long-distance acoustic signals.
description: Clink and Lau Electronic Supplementary Material: Data collection
 and acoustic analysis protocols for all datasets included in the present
 analysis. Tarsiers [1]<br> Data
 collection<br> Data were collected July and August 2018 in Tangkoko
 National Park, Sulawesi, Indonesia. We collected data using a combination
 of focal recordings and autonomous recorders. For focal recordings, we
 used a RØDE NT-USB Condenser Microphone (Røde Microphones, Sydney,
 Australia) connected to a 32 GB Apple iPad Air (Apple Inc., Cupertino, CA)
 and the Voice Record Pro application at a sampling rate of 44.1 kHz and 16
 bits. We used 2 different autonomous recording devices, an ARBIMON
 portable recorder which recorded at 44.1 kHz and 16 bits, or a SWIFT
 recorder which recorded at 48 kHz and 16 bits. Acoustic
 analysis<br> We downsampled the data with a 48 kHz sampling to a
 sampling rate of 44.1 kHz using Audacity(R) 2.3.0 software (2018). We
 created spectrograms using Raven Pro 1.5 Sound Analysis Software.
 Spectrograms were created with a 1600- point (33.3 ms) Hann window (3 dB
 bandwidth . 43.1 Hz), with 50% overlap, and a 2048-point discrete Fourier
 transform, yielding time and frequency measurement precision of 16.7 ms
 and 24.1 Hz. Titi monkeys [2,3]<br> Data
 collection<br> Titi monkey duets were recorded opportunistically at
 the California National Primate Research<br> Center (CNPRC), Davis,
 CA, USA each morning between 06:00 and 07:30 from March 2017 to March
 2019. We used a Marantz PMD 660 flash recorder and a Marantz Professional
 Audio Scope SG-5B directional condenser microphone. We recorded at a
 sampling rate of 44.1 kHz and 16-bit resolution.
 Acoustic analysis<br> We created spectrograms using Raven
 Pro 1.5 Sound Analysis Software. We generated spectrograms with a
 512-point (11.6 ms) Hann window (3 dB bandwidth = 124 Hz), with 75%
 overlap, and a 1024-point DFT, yielding time and frequency measurement
 precision of 2.9 ms and 43.1 Hz.  Gibbon duets (female
 introduction and trills; male codas [4,5])<br> Data
 collection<br> We collected recordings from gibbons at seven sites
 across Sabah, Malaysia during multiple field seasons from January 2013 to
 September 2016. We recorded<br> vocalizations at a sampling rate of
 44.1 kHz and 16-bit size using a Marantz PMD 660 flash recorder (Marantz,
 Kawasaki, Kanagawa Prefecture, Japan) equipped with a<br> Røde NTG-2
 directional condenser microphone (Røde Microphones, Sydney,
 Australia). Acoustic analysis<br> We created
 spectrograms using the Raven Pro 1.5 sound analysis with a 512-point (11.6
 ms) Hann window (3 dB bandwidth ± 124Hz), with 75% overlap, and a
 1024-point discrete Fourier transform, yielding time and frequency
 measurement precision of 2.9ms and 43.1 Hz. For the female calls we used
 the band-limited energy detector in Raven Pro to identify individual notes
 from each great call. Gibbon male solos [6]<br>
 Data collection<br> We collected data using Swift autonomous
 recording units in Danum Valley Conservation Area (11 recording units;
 March–July 2018) and in Maliau Basin Conservation Area (four recording
 units; August 2019), Sabah, Malaysia. The units in Danum Valley
 Conservation Area recorded at a sampling rate of 16 kHz and the units in
 Maliau Basin recorded at a sampling rate of 48 kHz. For both recording
 locations, we recorded at a sample size of 16 bits and at a gain of 40
 dB. Acoustic analysis<br> We created spectrograms
 in Raven Pro 1.6.We downsampled the 48 kHz recordings to 16 kHz.  We then
 made spectrograms with a 1024-point (64.0 ms) Hann window (3 dB bandwidth
 = 22.5 Hz), with 50% overlap, and a 1024-point discrete Fourier transform,
 yielding time and frequency measurement precision of 32 ms and 15.6
 Hz. Works Cited<br> 1.    Clink DJ, Tasirin JS,
 Klinck H. 2019 Vocal individuality and rhythm in male and female duet
 contributions of a nonhuman primate. Curr. Zool. 0, 1–14. <br> 2.  
  Clink DJ, Lau AR, Bales KL. 2019 Age-related changes and vocal
 convergence in titi monkey duet pulses. Behaviour 156, 1471–1494.
 (doi:10.1163/1568539X-00003575)<br> 3.    Lau AR, Clink DJ, Bales
 KL. 2020 Individuality in the vocalizations of infant and adult coppery
 titi monkeys (Plecturocebus cupreus). Am. J. Primatol.
 (doi:10.1002/ajp.23134)<br> 4.    Lau A, Clink DJ, Crofoot MC,
 Marshall AJ. 2018 Evidence for High Variability in Temporal Features of
 the Male Coda in Müller’s Bornean Gibbons (Hylobates muelleri). Int. J.
 Primatol. 39, 670–684. <br> 5.    Clink DJ, Grote MN, Crofoot MC,
 Marshall AJ. 2018 Understanding sources of variance and correlation among
 features of Bornean gibbon (Hylobates muelleri) female calls. J. Acoust.
 Soc. Am. <br> 6.    Clink DJ, Hamid Ahmad A, Klinck H. 2020 Brevity
 is not a universal in animal communication: evidence for compression
 depends on the unit of analysis in small ape vocalizations. R. Soc. Open
 Sci. 7.