Preliminary investigation into the differences in vocalisations between wild saki monkeys (Pithecia spp.)

Abstract

Information on primate vocalisations can be applied in several ways, including: improving captive welfare, as a census tool for cryptic species, or to investigate the impacts of anthropogenic disturbance on species’ behaviour (Delgado and van Shaik, 2000; Konrad and Geissman, 2006; Jacobsen et al., 2010). Vocalisations can be used as a taxonomic tool, and structural differences between calls have been used to compare a wide variety of taxa, including species of gibbon (Hylobatidae spp., Ruppell, 2010), marmosets (Callithrix spp., Mendes et al., 2009), owls (Strigidae spp., Flint et al., 2015), wolves (Canis spp., Kershenbaum et al., 2016), and galagos (Galagidae spp., Svensson et al., 2017). Additionally, differences in voca- lisations across taxonomic groups can be used to help determine genetic distances between species or investigate why vocal behaviours evolved (Blumstein and Armitage, 1998; Ord and Garcia-Porta, 2012).

Full text

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PRELIMINARY INVESTIGATION INTO THE
DIFFERENCES IN VOCALISATIONS BETWEEN
WILD SAKI MONKEYS (PITHECIA SPP.)
Jen Muir
Adrian A. Barnett
Magdalena S. Svensson
Introduction
Information on primate vocalisations can be applied in
several ways, including: improving captive welfare, as a
census tool for cryptic species, or to investigate the im-
pacts of anthropogenic disturbance on species’ behaviour
(Delgado and van Shaik, 2000; Konrad and Geissman,
2006; Jacobsen et al., 2010). Vocalisations can be used
as a taxonomic tool, and structural dierences between
calls have been used to compare a wide variety of taxa,
including species of gibbon (Hylobatidae spp., Ruppell,
2010), marmosets (Callithrix spp., Mendes et al., 2009),
owls (Strigidae spp., Flint et al., 2015), wolves (Canis spp.,
Kershenbaum et al., 2016), and galagos (Galagidae spp.,
Svensson et al., 2017). Additionally, dierences in voca-
lisations across taxonomic groups can be used to help de-
termine genetic distances between species or investigate
why vocal behaviours evolved (Blumstein and Armitage,
1998; Ord and Garcia-Porta, 2012).
One primate group that recently has been revised ta-
xonomically is the genus Pithecia, the saki monkeys, in
which ve species were previously described: P. mona-
chus, P. aequatorialis, P. irrorata, P. albicans, and P. p i t he -
cia (Hershkovitz, 1987). Aer a review of morphological
data, the group was rearranged into 16 species, including
three subspecies elevated to full species and ve newly
described species (Marsh, 2014). It has been suggested
that taxonomic research should utilize several disciplines
in combination so as to decrease the risk of inaccurate
conclusions (Schlick-Steiner et al., 2010). In the case of
the sakis, the use of purely morphological features opens
the opportunity for the taxonomic conclusions to be tes-
ted by evidence based on genetic structure, behaviour,
ecology, or life history, among others.
In the current study, vocalisations produced by wild
golden-faced sakis, Pithecia chrysocephala, white-faced
sakis, P. pithecia, and Equatorial sakis, P. aequatorialis,
were compared to study how calls might dier between
closely related species (P. pithecia and P. chrysocephala),
and whether any features were conserved across more
evolutionarily separated species (P. chrysocephala and P.
pithecia compared to P. aequatorialis). Before the reclas-
sication of Pithecia by Marsh (2014), P. chrysocephala
was considered a subspecies of P. pithecia, and so these
taxa were expected to display similar vocalisations.
Methods
Study Species
Pithecia chrysocephala, P. pithecia, and P. aequatorialis all
occupy forest habitats, including Amazonian várzea, iga-
pó, and terra rme forests. However, the species occupy
dierent geographical areas (Fig. 1), with P. chrysocepha-
la occurring within the Brazilian states of Amazonas,
Pará, and Roraima, and P. pithecia found in the states of
Pará and Amapá, as well as in the countries of Venezuela,
Guyana, French Guiana and Suriname (Marsh, 2014). Pi-
thecia aequatorialis is present only in central Peru (Marsh
and Heymann, 2018).
Data Organisation and Analysis
We collected vocalisation data for Pithecia chryso-
cephala in June-August 2018 in Manaus, Brazil (-3.083,
59.983) (for methodology and vocal repertoire see Muir
et al., 2019). We then gathered vocalisation data on two
other Pithecia species from previous published studies,
which we re-analysed and compared across species. For
P. pithecia, data from Henline’s (2007) study conducted
in Isla Redonda, Venezuela (7.766, – 62.883) was used,
and P. aequatorialis data came from Keiren’s (2012)

Neotropical Primates 27(1), July 2021 33
study in the Tahuayo River Amazon Research Center,
Peru (-4.383, – 73.25). While Henline’s (2007) study was
conducted before the reclassication of Pithecia species,
it is clear that this study did not include vocalisation
from P. chrysocephala as the in-situ part of the study was
conducted in Venezuela, far from the natural range of
this species, but within that P. pithecia. Our study and
the two previous studies each report between 5 and 12
distinct vocalisations per species (Table 1). One limita-
tion of these studies is that individual sakis could not be
distinguished during recordings and so pseudo-replica-
tion is a potential issue as it is unknown how much any
given individual contributed to the sample.
Table 1. e complete adult vocal repertoires of P. chrysocephala,
P. pithecia, and P. aequatorialis as recorded by Muir et al. (2019),
Henline (2007), and Keiran (2012). P. aequatorialis calls were not
put into groups within their study and so have been grouped ac-
cording to their similarity to the others based on their description
and/or behavioural context.
Group Pithecia
chrysocephala
Pithecia
pithecia
Pithecia aequatorialis
Whistles Whistle
(n = 778)
Pee (n = 20) Bird (n = 23)
See (n = 6) Chits (n = 61)
Chew (n=8) Chits/XX (n = 10)
Chucks Chuck
(n = 212)
Chuck
(n = 16)
Bark (n = 45)
Chits with Bark
(n = 6)
Churk
(n = 1)
Croak (n = 2)
Yip (n = 1)
Trills Trill (n = 253) Cheeyeep
(n = 29)
Trill (n = 5)
Seeyeep
(n = 5)
Peeyeep
(n = 2)
Warbled
Trill (n = 8)
Purrs Soft Growl
(n = 4)
Soft Growl
(n = 3)
Growl (n = 17)
Moans and
Alarms
roat Rattle
(n = 96)
roat
Rattle
(n = 9)
Scream (n = 3)
Z-trill
(n = 3)
Unknown Grunt (n = 1)
Results
From spectrograms, Pithecia chrysocephala and P. p i t h e -
cia display similar chuck calls, while P. chrysocephala and
P. aequatorialis show similar throat rattle/scream calls, as
well as juvenile cry/juvenile yip calls (Fig. 2, Table 2). Ad-
ditionally, these calls are similarly used in alarm, antago-
nistic, and parent-ospring contact, respectively.
One-sample t-tests suggested that Pithecia chrysocephala
and P. pithecia dier signicantly in the duration of their
chuck calls, t(217) = 2.11, p =.036, and in fundamental fre-
quency, t(217) = 15.191, p < .001. is was also suggested
for the duration, t(95) = 21.575, p < .001, and fundamen-
tal frequency, t(95) = 3.445, p = .001, of the throat rattle
call. Comparisons between the P. chrysocephala throat
rattle and P. aequatorialis scream were also conducted,
Figure 1. Location of study site and distributions of the studied
Pithecia species. Map created using spatial data obtained from
IUCN (Marsh et al. 2018a; Marsh et al. 2018b; Marsh and Hey-
mann 2018).
In our study calls were initially compared visually by
spectrograms from each paper, with similar calls then
being statistically compared in terms of acoustic mea-
surements. Similarity in terms of the behavioural con-
text of the calls was also considered. Call measurements
of duration and fundamental frequency were taken us-
ing the speech analysis program Praat (Boersma, 2001).
One sample t-tests were performed using SPSS v.25 to
compare call features between species as the raw data
was not available for P. pithecia and P. aequatorialis.
When making comparisons, the two calls within Hen-
line’s (2007) chucks group were averaged to allow for
a comparison with the graded chuck call found in P.
hrysocephala (Table 1). e whistle and trill groups were
not compared in this manner as the calls within them
appeared to dier from those of P. chrysocephala when
shown as spectrograms. e so growl group was also
not compared, due to a small sample size for both P.
pithecia and P. chrysocephala. From Keiran’s (2012) study
of P. aequatorialis, only the scream and juvenile yip calls
were similar enough on spectrograms to be compared
(to the P. chrysocephala throat rattle and juvenile cry,
respectively).

Neotropical Primates 27(1), July 202134
with results suggesting that they dier signicantly in
fundamental frequency, t(95) = 55.401, p < .001, but not
in duration, t(95) = .671, p = .504. e P. chrysocephala
juvenile cry and P. aequatorialis juvenile yip call diered
signicantly in duration, t(107) = 15.619, p < .001and
fundamental frequency, t(107) = 35.503, p < .001.
Figure 2. Spectrograms of the vocal repertoires of Pithecia chrysocephala, P. pithecia, and P.
aequatorialis, with visually similar calls. Calls include: P. pithecia chuck (a), P. chrysocephala
chuck (b), P. chrysocephala throat rattle (c), P. aequatorialis scream (d), P. chrysocephala juvenile
cry (e) and P. aequatorialis juvenile yip (f).
Table 2. Structural properties of structurally and contextually similar calls between Pithecia chry-
socephala, P. pithecia, and P. aequatorialis.
Species Compared Calls Compared Mean Duration in
Seconds
Mean Fundamental
Frequency in Hz
P. chrysocephala
P. pithecia
Chuck
Chuck
0.352
0.335
6307.10
6507.15
P. chrysocephala
P. aequatorialis
roat rattle
Scream
1.537
1.554
3029.84
784.38
P. chrysocephala
P. aequatorialis
Juvenile cry
Juvenile yip
0.419
0.158
6486.16
766.73
Discussion
At a glance, structural properties between Pithecia pithe-
cia calls in Henline (2007) and those of the current study
of P. chrysocephala are very similar, with chucks being the
shortest calls, throat rattles the longest, chucks and trills
at the highest frequencies, and so growls at the lowest.
However, few calls between these species were sucient-
ly similar on spectrograms to be compared statistically.
All visually similar calls among P. chrysocephala, P. pi t he -
cia and P. aequatorialis were found to have dierences in
their structure in terms of their fundamental frequency.
ese preliminary ndings add to the morphological evi-
dence presented by Marsh (2014) on the distinctness of
Pithecia taxa, supporting the classication of P. chryso-
cephala as a separate species from P. pithecia, rather than
a subspecies. However, as only one population of each
species was studied, the possibility of variations within
populations of a single evolutionary unit must be consi-
dered before any more substantial claims can be made.
e calls of Pithecia aequatorialis appeared notably less
similar to P. chrysocephala than P. pithecia, potentially
reecting the greater evolutionary distance between
these species. Phylogenetic dierences in call struc-
ture across a genus have been previously observed in
a number of primate taxa, including sportive lemurs,
Lepilemur spp., in which species that were less closely
related to each other had more distinctly dierent calls
(Mendez-Cárdenas et al., 2008). Similar results have
been obtained with titi monkeys, Callicebinae sp., (Ar-
det et al., 2018). It is also possible that these calls are
conserved across the genus, similar to how the startle
call is conserved across mouse lemurs, Microcebus spp.
(Zimmerman, 2012).

Neotropical Primates 27(1), July 2021 35
Future studies could usefully investigate dierences
among Pithecia populations and examine the inuence
of habitat dierences on vocalisations. It would also be
interesting to investigate Pithecia vocal behaviour in the
context of all pitheciids, as several similarities are evi-
dent throughout this group (Bezerra et al., 2017). For
example, the tcho calls, whistles, and loud screams of gol-
den-backed uacaris, Cacajao ouakar y, are similar to the
P. chrysocephala chucks, whistles, and throat rattles res-
pectively (Bezerra et al., 2010). Likewise, juvenile B-calls
(an alarm call) of black-fronted titi monkeys, Callicebus
nigrifrons, are similar to juvenile P. chrysocephala peeps,
as are the juvenile purrs of red-bellied titi monkeys, Plec-
turocebus moloch, to juvenile golden faced saki trews
(Moynihan, 1966; Berthet et al., 2018). Additionally, the
chucks and intergroup call/throat rattle of Plecturocebus
moloch and Pithecia chrysocephala resemble each other
(Moynihan, 1966; Caselli et al., 2014). More wide-sca-
le comparisons across all pitheciid species could also be
conducted to examine the social and ecological eects
on the evolution of their communication, and why such
calls appear to be similar. However, a full phylogenetic
comparison of Pithecia vocalisations is currently limited
by a lack of data, and so further studies of Pithecia and
pitheciid species are recommended. e development of
a pitheciid vocalisation database as suggested by Bezerra
et al. (2017) would be ideal for this purpose.
Acknowledgements
We would like to thank Makiko Take and Tianara So-
broza for their assistance in Brazil. We would also like to
thank Instituto National de Pesquisas da Amazonia for
providing the opportunity to carry out this project, and
for Santander for providing a Student Project Grant.
Jen Muir, School of Social Sciences, Oxford Brookes
University, Oxford OX3 0BP, UK, E-mail: <jenmuir93@
gmail.com>, Adrian A. Barnett, Amazon Mammal Re-
search Group, Biodiversity Studies, Instituto National de
Pesquisas da Amazonia, Manaus, Brazil, and Magdalena
S. Svensson, School of Social Sciences, Oxford Brookes
University, Oxford OX3 0BP, UK.
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FIRST RECORD OF BROWN HOWLER MONKEYS
IN SÃO PEDRO DA ALDEIA, RIO DE JANEIRO,
BRAZIL
Fabio Mostacato Bastos
Bruno Coutinho Kurtz
Luís Fernando Faulstich Neves
Leonardo de Carvalho Oliveira
Introduction
e discovery of a threatened species in a new locality
provides important information to reassess its extent of
occurrence, area of occupancy, and conservation status
(IUCN, 2019). In times where human-induced defau-
nation in forest fragments is of major scientic concern
(Canale et al., 2012; Dirzo et al., 2014; Galleti et al.,
2016) and outbreaks of yellow fever virus are severely
impacting populations of wild non-human primates in
Brazil’s Atlantic Forest (Holzmann et al., 2010; Almeida
et al., 2012; Bicca-Marques et al., 2017), the discovery of
a group of threatened primate species in a small fragment
of Atlantic Forest should be celebrated.
We report here the rst record of a group of brown howler
monkeys, Alouatta guariba clamitans, in São Pedro da
Aldeia, Rio de Janeiro, Brazil. A. guariba is the primate
species with most records and with the largest distribu-
tion in the Atlantic Forest (Culot et al., 2019). In Rio
de Janeiro state brown howlers inhabit the coastal and
the northern regions (Gregorin, 2006), with populations
occurring in at least 23 protected areas (Bicca-Marques
et al., 2018). e deforestation and fragmentation of the
southern and southeastern forests have played an impor-
tant role in decreasing its current distribution compared
to its historical occurrence (Bicca-Marques et al., 2018).
It is currently listed as a Vulnerable species on the IUCN
Red List of reatened Species, with ongoing population
decline (Jerusalinsky et al., 2020).
Study site
Our study site (22°43'20.02"S, 42°07'25.37"W) is a small
patch of lowland seasonal semideciduous forest with 36
ha. It has an elliptical shape, with altitude varying from 7
to 35 m above sea level. Locally known as Ilha dos Maca-
cos (Monkeys’ Island), it is connected to other fragments
of Atlantic Forest totaling about 418 ha (Fig. 1). e site
lies in a swampy plain bordered by two small rivers that
drain northward up to the basin’s main river, Rio Una.
Grassy elds characterize the landscape. e rainy sea-
son (December-May) turns most of the plain into wet-
lands. e forest fragment studied lies in a higher terrain
so that waters reach only part of its border. Cattle ran-
ching, eucalyptus forestry and agriculture characterize
local land use around the fragment (Bastos, 2020). e
local climate is an interface between two Köppen-Geiger
climate classes, Aw and BSh (Barbiéri, 1984, 1997), and
the precipitation is between 900-1,000 mm per year (Pin-
to et al., 2011).
Results and discussion
During our survey focused on oristic and phytosocio-
logical data collection (Bastos, 2020), we unexpectedly
heard howls at the study site. erefore, we decided to
collect ad libitum data (Altmann, 1974) on all monkey
observations during every visit. We registered howler
vocalizations in 10 of 31 visits. e records encompas-
sed two years, from May 2018 to February 2020. e
only visualization was in January 2020. We observed an