DOI: 10.5061/dryad.nvx0k6dsn
title: The vocal repertoire of the bearded capuchin (Cebidae: Sapajus libidinosus): implications for understanding the complexity of neotropical primate communication

description: Vocal communication is an essential aspect of primate social behaviour.
 The bearded capuchin Sapajus libidinosus is endemic to Brazil and some
 studies have described specific vocalisation types for this species;
 however, there is still no complete description of its vocal repertoire.
 Thus, this study aimed to describe the vocal repertoire of a group of S.
 libidinosus living in the Parque Nacional de Brasília (PNB), a protected
 area in the Cerrado area of Central Brazil. We carried out focal samplings
 and recording of vocalisations of members of a S. libidinosus troop in
 different behavioural contexts. The call analyses revealed 25 different
 types of vocalisations, and each call presented significant structural
 variation. We grouped these vocalisations according to the context of the
 emission or acoustic structure into the following categories: contact
 calls (contact note, infant babbling, trill, teeth- and lip-smacking, and
 sirena); foraging calls (chihui, grgr, and patinado); whistle series (WS;
 food-associated WS, long-distance WS, and inter-group encounter WS);
 aggressive calls (aggressive contact note, ascending rapid staccato, cough
 cough, and pip); calls in response to aggression (scream, squeal, and
 pulsed scream), sexual display calls (chuck and raspy oestrous call), and
 stress-related calls (alarm call/ bark, hiccup, hip, double hip, and wah
 wah). S. libidinosus presented a very rich vocal repertoire, revealing a
 pattern consistent with the repertoire of other capuchin monkey species.
 This is the first comprehensive description of the S. libidinosus vocal
 repertoire and highlights the complexity of neotropical primate
 communication. Vocal communication is an essential aspect of primate
 social behaviour. The bearded capuchin Sapajus libidinosus is endemic to
 Brazil and some studies have described specific vocalisation types for
 this species; however, there is still no complete description of its vocal
 repertoire. Thus, this study aimed to describe the vocal repertoire of a
 group of S. libidinosus living in the Parque Nacional de Brasília (PNB), a
 protected area in the Cerrado area of Central Brazil. We carried out focal
 samplings and recording of vocalisations of members of a S. libidinosus
 troop in different behavioural contexts. The call analyses revealed 25
 different types of vocalisations, and each call presented significant
 structural variation. We grouped these vocalisations according to the
 context of the emission or acoustic structure into the following
 categories: contact calls (contact note, infant babbling, trill, teeth-
 and lip-smacking, and sirena); foraging calls (chihui, grgr, and
 patinado); whistle series (WS; food-associated WS, long-distance WS, and
 inter-group encounter WS); aggressive calls (aggressive contact note,
 ascending rapid staccato, cough cough, and pip); calls in response to
 aggression (scream, squeal, and pulsed scream), sexual display calls
 (chuck and raspy oestrous call), and stress-related calls (alarm call/
 bark, hiccup, hip, double hip, and wah wah). S. libidinosus presented a
 very rich vocal repertoire, revealing a pattern consistent with the
 repertoire of other capuchin monkey species. This is the first
 comprehensive description of the S. libidinosus vocal repertoire and
 highlights the complexity of neotropical primate communication.
description: <i>Study site and
 subjects</i> The study was conducted
 between September 2018 and June 2019 in Parque Nacional de Brasília (PNB),
 a protected area located in Distrito Federal, Central Brazil
 (15°35'–15°45' S, 48°50'–48°53' W). The study area was
 a gallery forest fragment, a phytophysiognomy of the Cerrado. Within the
 fragment, an area containing two artificial swimming pools was open to the
 public, where the subject animals often interacted with humans.
 We observed a group of ten bearded capuchins, comprising five
 adults (three males and two females), one subadult male, one juvenile
 female, and three infants.  <i>Data collection /
 Recording vocalisations</i> We used focal animal sampling
 [Altmann, 1974] to collect data on the bearded capuchin group's vocal
 repertoire. We recorded vocalisations using a  shotgun microphone
 connected to a digital recorder. Each focal session lasted 10–15 min, in
 which we followed the focal subject, recorded all emitted vocalisations,
 and recorded the behavioural context. Each time the focal animal
 vocalised, we dictated its activities to a headset microphone connected to
 the same digital recorder. We didn’t record infant vocalisations during
 focal sessions. Occasionally, we used <i>ad libitum</i>
 sampling [Altmann, 1974], and we included the calls recorded by this
 method to describe the bearded capuchins' vocal repertoire. We
 registered the activities of the focal animal according to the following
 behavioural categories: foraging (searching, approximating, manipulating,
 or inspecting a food item), feeding (ingesting a food item), locomoting
 (walking or running), resting (sitting or lying), and interacting
 (playing, attacking, grooming, or copulating). We registered other
 behaviour categories, such as sharing food items, specific body postures
 or displays, and interactions with humans. 
 <i>Data
 analysis</i> We saved each call recorded
 during sampling as an individual WAV file, from which we later produced
 spectrograms. We classified each call based on its acoustic structure and
 sound. We followed the classification used by Di Bitetti [2001] and Di
 Bitetti and Wheeler [2017] for <i>S. nigritus</i>. We named
 the vocalisations following Di Bitetti and Wheeler [2017]. After this
 first classification, we further selected high-quality files, removing
 those with excessive background noise, and proceeding with acoustic
 measurements. Only calls with more than ten high-quality samples files
 were used, resulting in the measurement of ten call types
 (<i>n</i> = 389 files). In general, all individuals
 contributed to the samples for each call type in the analysis. The
 exceptions were the sirena and raspy oestrous calls, which only had
 samples from males, and the teeth- and lip-smacking calls that only had
 samples from the juvenile female and one adult male. We used
 Fourier-transformed spectrograms, using the Avisoft-SASLab Pro v5.2.14
 software (Avisoft Bioacoustics, Berlin, Germany), with the following
 settings: FFT-length = 1024, Frame = 100%, Hamming window, and 50%
 overlap. Whenever necessary, we used the finite impulse response (FIR)
 filter, high- and low-pass filters to remove noise that did not overlap
 with the vocalisations. As the call types were very
 different in structure, we used simple acoustic variables that could be
 measured in all call types, based on the work of Di Bitetti and Wheeler
 [2017]. We measured the following variables from the selected
 spectrograms: number of elements in a call, call duration, duration of the
 longest element, initial peak frequency, peak frequency at the end,
 maximum peak frequency, minimum peak frequency, range of spectral energy,
 peak frequency on the mean spectrum, and change in frequency from start to
 end. We took measurements on the whole call when it had more than one
 element. We measured all variables at the fundamental harmonic of the call
 using automatic measurements in Avisoft-SASLab software. We checked the
 resulting values manually using a cursor at the spectrograms and then
 transferred automatically to an Excel spreadsheet.
 To test the classification of
 the calls based on the measured acoustic variables, we performed a
 discriminant function analysis (DFA) with a cross-validation method, using
 the LDA function of the MASS package [Venables and Ripley, 2002] in R
 software [R Core Team, 2020]. Since the acoustic variables had different
 scales, we standardised the acoustic variables using the
 <i>z</i>-score method before performing the DFA. All variables
 were centred at zero, with a variance of one. One of the premises of LDA
 is that the number of acoustic variables in the model cannot exceed the
 number of calls assigned to each call type [James et al., 2013].
 Therefore, we included only call types with more than ten samples in the
 analyses since we measured ten acoustic variables. First, we randomly
 divided the samples into two subsamples of the same size. One subsample
 served as a training sample to construct the discriminant function, while
 the other was the test sample used to verify how well the discriminant
 function assigned vocalisations to their <i>a priori</i>
 categories. After the cross-validation process, we performed a permutation
 test to compare the number of correct classifications with that expected
 in 1000 random permutations [Slow, 1990].
description: The data set is composed by three files,
 "Acoustic_Measurements.xls" contains the measured acoustic
 variables that were used to perform our analysis (columns 6 – 15), columns
 1 – 3 contains information about the sex, age and identity of the
 individual that emitted the call, column 4 contains the call type and
 column 5 contains the file name that were used to take the measurements.
 The file entitled "measured_calls.rar" contains the 389 call
 files that were used to take the acoustic measurements.  The third file,
 "25_calls.rar", contains one example of each of the 25 Sapajus
 libidinosus' call types that were described in our work.