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Bioacoustics of the black-headed night monkey, Aotus nigriceps

ISSN 1413-4703
A J ou rn al of th e Neotropical Section of the
IUCN/SSC Primate Specialist Group
Volume 24
Number 1
June 2018
Erwin Palacios
Bruna Bezerra
Jessica Lynch Alfaro
Liliana Cortés Ortiz
Júlio César Bicca-Marques
Eckhard Heymann
Anita Stone
News and Book Reviews
Brenda Solórzano
Ernesto Rodríguez-Luna
PSG Chairman
Russell A. Mittermeier
PSG Deputy Chairman
Anthony B. Rylands
Neotropical Primates
A Journal of the Neotropical Section of the IUCN/SSC Primate Specialist Group
Conservation International
2011 Crystal Drive, Suite 500, Arlington, VA 22202, USA
ISSN 1413-4703 Abbreviation: Neotrop. Primates
Erwin Palacios, Conservación Internacional Colombia, Bogotá DC, Colombia
Bruna Bezerra, Universidade Federal de Pernambuco, Recife, Pernambuco, Brasil
Jessica Lynch Alfaro, Institute for Society and Genetics, University of California-Los Angeles, Los Angeles, CA, USA
Liliana Cortés Ortiz, Museum of Zoology, University of Michigan, Ann Arbor, MI, USA
Júlio César Bicca-Marques, Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, Brasil
Eckhard Heymann, Deutsches Primatenzentrum, Göttingen, Germany
Anita Stone, Museu Paraense Emílio Goeldi, Belém, Pará, Brazil
News and Books Reviews
Brenda Solórzano, Instituto de Neuroetología, Universidad Veracruzana, Xalapa, México
Ernesto Rodríguez-Luna, Instituto de Neuroetología, Universidad Veracruzana, Xalapa, México
Founding Editors
Anthony B. Rylands, Conservation International, Arlington VA, USA
Ernesto Rodríguez-Luna, Instituto de Neuroetología, Universidad Veracruzana, Xalapa, México
Editorial Board
Hannah M. Buchanan-Smith, University of Stirling, Stirling, Scotland, UK
Adelmar F. Coimbra-Filho, Academia Brasileira de Ciências, Rio de Janeiro, Brazil
Carolyn M. Crockett, Regional Primate Research Center, University of Washington, Seattle, WA, USA
Stephen F. Ferrari, Universidade Federal do Sergipe, Aracajú, Brazil
Russell A. Mittermeier, Conservation International, Arlington, VA, USA
Marta D. Mudry, Universidad de Buenos Aires, Argentina
Anthony Rylands, Conservation International, Arlington, VA, USA
Horácio Schneider, Universidade Federal do Pará, Campus Universitário de Bragança, Brazil
Karen B. Strier, University of Wisconsin, Madison, WI, USA
Maria Emília Yamamoto, Universidade Federal do Rio Grande do Norte, Natal, Brazil
Primate Specialist Group
Chairman, Russell A. Mittermeier Deputy Chair, Anthony B. Rylands
Vice Chair, Special Section on Great Apes, Liz Williamson
Vice Chair, Special Section on Small Apes, Benjamin M. Rawson
Regional Vice Chairs—Neotropics
Mesoamerica, Liliana Cortés-Ortiz
Andean Countries, Erwin Palacios and Eckhard W. Heymann
Brazil and the Guianas, M. Cecília M. Kierul, Fabiano R. de Melo and Mauricio Talebi
Regional Vice Chairs —Africa
W. Scott McGraw, Janette Wallis and David N.M. Mbora
Regional Vice Chairs —Madagascar
Christoph Schwitzer and Jonah Ratsimbazafy
Regional Vice Chairs — Asia
China, Long Yongcheng
Southeast Asia, Jatna Supriatna, Christian Roos, Ramesh Boonratana and Benjamin M. Rawson
South Asia, Sally Walker and Sanjay Molur
Layout: Patricia Salinas Garzón, Bogotá, DC <>
IUCN/SSC Primate Specialist Group logo courtesy of Stephen D. Nash, 2002.
Front cover: Black titi monkey (Plecturocebus cinerascens). Photo taken at Guaporé River, Municipality of Comodoro, Mato Grosso, Brazil. July 2015.
Photo taken by Breno Dias Vitorino.
is issue of Neotropical Primates was kindly sponsored by the Margot Marsh Biodiversity Foundation, 432 Walker Road, Great Falls, Virginia 22066,
USA, and the Los Angeles Zoo, Director John R. Lewis, 5333 Zoo Drive, Los Angeles, California 90027, USA.
Neotropical Primates 24(1), June 2018 29
Soziobiologie, Deutsches Primatenzentrum, Kellnerweg 4,
D-37077 Göttingen, Germany.
Baker, A. J. and Dietz, J. M. 1996. Immigration in wild
groups of golden lion tamarins (Leontopithecus rosalia).
Am. J. Primatol. 38: 47–56.
Clutton-Brock, T. H., Russell, A. F., Sharpe, L. L., Broth-
erton, P. N. M., McIlrath, G. M. and Cameron, E. Z.
2001. Eects of helpers on juvenile development and
survival in meerkats. Science. 293: 2446–2449.
Culot, L., Lledo Ferrer, Y., Hoelscher, O., Muñoz Lazo,
F. J. J., Huynen, M. C. and Heymann, E. W. 2011. Re-
productive failure, possible maternal infanticide and can-
nibalism in wild moustached tamarins, Saguinus mystax.
Primates. 52: 179–186.
Garber, P. A., Moya, L., and Malaga, C. 1984. A prelimi-
nary eld study of the moustached tamarin monkey (Sa-
guinus mystax) in northeastern Peru: questions concerned
with the evolution of a communal breeding style. Folia
Primatol. 42: 17–32.
Goldizen, A. W. 1988. Tamarin and marmoset mating sys-
tems: unusual exibility. Trends Ecol. Evol. 3: 36–40.
Goldizen, A. W., Mendelson, J., van Vlaardingen, M.
and Terborgh, J. 1966. Saddle-back tamarin (Saguinus
fuscicollis) reproductive strategies: Evidence from a thir-
teen-year study of a marked population. Am. J. Primatol.
38: 57–8.
Heymann, E. W. 1995. Sleeping habits of tamarins, Sa-
guinus mystax and Saguinus fuscicollis (Mammalia; Pri-
mates; Callitrichidae), in north-eastern Peru. J. Zool.
237: 211–226.
Jennions, M. D. and Macdonald, D. W. 1994. Cooperative
breeding in mammals. Trends Ecol. Evol. 9: 89–93.
Koenig, A. 1995. Group size, composition, and reproduc-
tive success in wild common marmosets (Callithrix jac-
chus). Am. J. Primatol. 35: 311–317.
Löttker, P., Huck, M. and Heymann, E. W. 2004. Demo-
graphic parameters and events in wild moustached tama-
rins (Saguinus mystax). Am. J. Primatol. 64: 425–449.
Pusey, A. E. and Packer, C. 1987. Dispersal and philopatry.
In: Primate societies, B. B. Smuts et al. (eds.), pp. 250–
266. University of Chicago Press, Chicago.
Savage, A., Giraldo, L. H., Soto, L. H. and Snowdon, C. T.
1996. Demography, group composition, and dispersal in
wild cotton-top tamarin (Saguinus oedipus) groups. Am.
J. Primatol. 38: 85–100.
Schaner, C. M. and French, J. A. 1997. Group size and
aggression: “recruitment incentives” in a cooperatively
breeding primate. Anim. Behav. 54: 171–180.
Stojan-Dolar, M. and Heymann, E. W. 2010a. Functions
of intermittent locomotion in mustached tamarins (Sagu-
inus mystax). Int. J. Primatol. 31 (5): 677–692.
Stojan-Dolar, M. and Heymann, E. W. 2010b. Vigilance
of moustached tamarins in single-species and mixed-spe-
cies groups—the inuence of group composition. Behav.
Ecol. Sociobiol. 64 (3): 325–335.
Weisser, W. W. 2001. e eects of predation on dispersal.
In: Dispersal, J. Clobert, E. Danchin, A. A. Dhont and J.
D. Nichols (eds.), pp. 180–188. Oxford University Press,
William D. Helenbrook
Leigh Preston
Noah A. Linck
Megan Quirk
Jessica A. Suarez
Only three studies have assessed Aotus vocalizations (known
as either owl or night monkeys). None of these studies
have assessed the black-headed night monkey (A. nigriceps)
found in southeastern Peru, northern Bolivia, and cen-
tral-western Brazil, nor have they focused on bioacoustics of
Aotus spp. in the wild. Of these three captive-based studies,
13 dierent call types have been described in A. lemurinus
(Andrew 1963; Moynihan 1964) and A. azarae (Kantha et
al. 2009). Most of these calls are distinct from one anoth-
er; however, there are some inconsistencies in naming that
need to be addressed, as described in Table 1. First, the
Trill described by Andrew (1963) has similar structure and
bandwidth to the Scream described by Moynihan (1964).
Moynihan does describe a Low Trill which is distinct from
the Trill in Andrew (1963), and the Low Trill described by
Kantha et al. (2009) does not resemble structure, band-
width, or call duration of the Trill in Andrew (1963) or the
Low Trill in Moynihan (1964). erefore, we suggest that
the Trill in Andrew (1963) is structurally distinct from the
Low Trill in Moynihan (1964), and the Low Trill in Kantha
et al. (2009) appears to be a distinct call from the other
two studies. Secondly, one of the representative Squeaks
described by Andrew (1963) is very similar to the Gru
Grunt (Moynihan 1964). Each has numerous harmonics,
a similar descending frequency across the exact call dura-
tion, and a very similar bandwidth. erefore, the Gru
Grunt should be renamed Squeak, as it was previously de-
scribed in Andrews (1963). irdly, the Squeak described
by Moynihan (1964) is structurally similar to the Twitter
described by Andrews (1963) and should be renamed.
Fourth, neither the Long Scream nor the Short Scream
described by Kantha et al. (2009) appear to be similar in
structure, bandwidth, or duration to the Scream in Moyni-
han (1964) and should potentially be renamed. Fifth, the
Moan described by Moynihan (1964) is not similar to the
Moan in Kantha et al. (2009) in structure, bandwidth, or
duration. e low frequency band is structurally similar to
a variant Low Trill described by Moyniahn 1964, though
the quality of the spectrogram in Kantha et al. (2009)
makes it dicult to conrm this possibility. And nally,
the Gulp described by Kantha et al. (2009) is similar to the
Gulp in Moynihan (1964); however, the bandwidth in the
Neotropical Primates 24(1), June 201830
Table 1. Vocal descriptions from all previously published captive and semi-captive Aotus studies. Several similar calls were found in both
Moynihan 1964 and Kantha et al. 2009, though both were included because they were found in dierent species and have dierent band-
width and duration.
Species Call type
Aotus lemurinus
griseimembra (a)
Twitter 2000-8000 40
Descending from 3.5-4 kHz to 2-3 kHz; Long rapid series once
every 200 msec. A fundamental frequency (2-4 kHz) with a
second harmonic at 5-8* kHz
Trill 1000-7000* 300 Series of Twitters
Aotus lemurinus
griseimembra (b)
Squeak 500-5000 100
"Guinea pig squeak" starting at lower frequency (500 Hz) and
rising steeply to 4-4 kHz; or, simply protracted lower frequency
(500-700 Hz)
Sharp Call 1000-15000 150-250 Sometimes sharp initial click. Once every 150-250 msec
Boom 150 1000+ Low soft call by vibration of false vocal cords
Low Trill 240-500* 600* Bubbling series of low-pitched notes, rapid but distinguishable
series. Varied from 3-12 notes
Gulp 0-650 100-260 Very common. Moderately loud and rather "liquid" sounding.
Uttered in series of 2 to 3 notes. Series repeats rapidly
Gru Grunt 100-4000* 100*
Most common. Uttered as singly or in short series of two to
ve notes. Successive notes uttered at slightly irregular intervals.
Longer pauses. Low-pitched, moderately long, and moderately
loud. Multiple harmonics
Squeak 1000-9500* 50* 1-3.5 kHz fundamental frequency, followed by two harmonics
ranging from 4-9.5 kHz
Sneeze Grunt 0-1000* 200*
Sneeze superimposed upon a loud Gru Grunt. Usually uttered
as a single note, though sometimes two in quick succession.
Often associated with Gulps, single Low or High Trill, or Moan
Resonant Grunts Unknown Unknown
More complex than Gru Grunt and rarer. Speed loudness,
and pitch varied considerably. Long series of 10-15 notes. Most
common series included soft and low notes rst half of series
(softer than Gru Grunt), and progressively louder towards
middle of series. Towards climax similarly loud, resonating, and
rapid. Finally, slowed in tempo, lower and softer
Aotus azarae (c)
Moan 220-480* 600*
Brief, soft, moan. Most common call type in captive individuals.
Often uttered along with other calls before or after, including
Low Trills, Gulps, and Sneeze Grunts
Scream 2000-8500* 800 High pitched but wavering. Quite prolonged. Multiple
harmonics (though an exact number not given)
Moan 140-300 500 No description given
Long Scream 2800-5800 260 No description given
Gulp 1800-5800 54 No description given
Low Trill 2000-3100 52 No description given
Short Scream 980-3300 190 No description given
Sneeze Grunt 1580-3310 50 No description given
earlier study is far less than 1 kHz, while the Kantha et al.
(2009) study shows an upper frequency of at least 10 kHz.
Based on the available data and without further descriptive
analysis in Kantha et al. (2009), these should likely be con-
sidered distinct calls.
Vocalization analysis for owl monkey species is particularly
important as it is dicult to dierentiate between individ-
uals or determine group dynamics because they are noc-
turnal. A vocal assessment could potentially be used to dif-
ferentiate individuals and assess group membership during
(a) Andrew 1963 (2 laboratory animals) and (b) Moynihan 1964 (12 semi-captive animals) originally classied as A. trivirgatus; (c) Kantha et al. 2009
(16 laboratory animals). *Estimates based solely on published spectrogram.
new group encounters simply based on bioacoustics (Salmi
et al. 2014). e objective of this study, consequently, was
to add to the Aotus bioacoustic literature by sampling sev-
eral geographically dispersed groups of wild A. nigriceps
(Fig. 1) in southeastern Peru.
Neotropical Primates 24(1), June 2018 31
Figure 1. Spectrogram images (left) and frequency distribution of calls (right) for three described calls: Twitter (High), Ch Ch, and Long
Trill. Frequency distributions represent upper frequency range (A), lower frequency range (B), and bandwidth (C) for each call. Box and
whisker represent mean, 1 standard deviation, and 2 standard deviations. For squeak, only low, high, and alto spectrograms are shown.
Ch ch calls shown as common pair.
Bioacoustic recordings were collected from eleven A.
nigriceps groups ranging in size from 2-5 individuals.
Sampling occurred April-May 2016, October-Novem-
ber 2016, and April 2017, for a total of twenty-eight
days at Villa Carmen Biological Station (12°53’39»S,
71°24’16”W) and nine days at Manu Learning Center
(CREES) research station (12°4722S 71°2332W) -
both in premontane rainforest. Seven groups were sam-
pled Villa Carmen and four groups at CREES, both lo-
cated on the edge of Manu National Park buer zone in
the Peruvian Amazon. Villa Carmen has a long history of
development, ecotourism and agriculture. Sampled areas
were largely dominated by secondary forest. At CREES,
groups were sampled in areas of rainforest regeneration.
Groups of 2-7 researchers searched for night monkey
groups from 5:30-7:30 am and 5:30-7:30 pm, times
when A. nigriceps groups are known to be active near their
nesting sites. Two recordings took place before 5:30 am,
when researchers left the eld station early to visit more
distant night monkey groups. Additional vocalizations
were heard during the day, though none were included
in this study. A Zoom H1 Handy Recorder was coupled
with a RØDE NTG-2 condenser shotgun microphone
and shoe shockmount on a micro boompole. Recordings
were collected at a sampling frequency of 48 kHz at a dis-
tance varying from 2-25 m. Certain groups were sampled
more extensively than others, due to logistic feasibility.
When feasible, behaviors associated with vocalizations
were categorized into three activities: resting, traveling,
or feeding. All calls were compared to the three previous
Neotropical Primates 24(1), June 201832
e Twitter was named after the similarly structured
Twitter call described by Andrew (1963), though mea-
surable dierences exist in number of harmonics and
bandwidth (Table 2). e Twitter was found in all but
one group and had up to 3 additional harmonics beyond
the fundamental frequency (191-553 Hz), ranging from
a mean of 1,755-2,847 Hz (High), to 3,666 4,140 Hz
(Alto), to 3,562 4,808 Hz (Ultra). e low fundamen-
tal frequency and high dominant harmonic were always
present in the Twitter, whereas the Alto and Ultra were
only found in single groups at Villa Carmen. e mean
bandwidth of the Ch Ch call was 1,611 9,961 Hz with
a mean duration of 183 msec.
Figure 2. Photo of the black-headed night monkey, Aotus nigri-
ceps. Photo credit: Jessica A. Suarez.
Aotus studies (Andrew 1963; Moynihan 1964; Sri Kan-
tha et al. 2009). Audio recordings were analyzed using
the spectral audio program Raven Pro 1.5 Sound Anal-
ysis Software (Cornell Lab of Ornithology Bioacoustics
Research Program, Ithaca, New York). Duration of calls,
dominant and fundamental frequencies, high and low
frequencies, and total bandwidth were then measured.
Amplitude was not analyzed because we could not control
for size or age of individuals. All recordings were con-
ducted non-invasively, minimized impact on behavior,
and avoided excessive disturbance, and the research was
therefore deemed exempt from the Institutional Animal
Care and Use Committee approval. All research adheres
to the principles for the ethical treatment of primates set
forth by Neotropical Primates. Audio les analyzed dur-
ing the current study are available from the correspond-
ing author on reasonable request through ResearchGate.
ree distinct calls were identied in our study, including
the Twitter (N = 165), Ch Ch (N = 122), and Long Trill
(N = 3) (Figure 2). In a limited number of cases, we were
able to note an associated behavior with calls. Of 46 High
Twitter calls, 47.8 % took place while the individual was
traveling and 52.1 % of calls took place while resting. Of
19 Ch Ch calls, 36.8 % were associated with travel, and
63.2 % with resting. No behaviors were recorded during
the Long Trill.
Table 2. Acoustic properties of three calls in wild black-headed night monkeys, Aotus nigriceps. e squeak is characterized by a funda-
mental frequency (low), and dominant frequency (high).
Call Type Bandwidth
Mea Duration
(msec) Description
Similar in structure of Twitter described by Andrew (1963), though additional harmonics
described here.
Ultra 3562-4808 49
Alto 3666-4140 20
High 1755-2847 43
Low 191-553 21
Ch Ch 1611-9961 183
Similar to Gulp described by Kantha et al. (2009); however, this name does not correspond
with the Gulp described by Moynihan (1964) which has a much lower frequency (<1000
Hz). erefore, we have renamed to reect a new call type.
Long Trill 470-3046 170 Similar to original Trill described by Andrew (1963) and the Scream described by Moynihan
(1964). ere are some structural dierences which is why we refer to it as the Long Trill
e Ch Ch call is similar to the Gulp described by Kantha
et al. (2009); however, this name does not correspond to the
Gulp described originally by Moynihan (1964). erefore,
we have renamed the call as an onomatopoeic description,
Ch Ch. e Ch Ch call was recorded as two closely paired
repetitive sounds in ten out of eleven groups (84.4 % of mea-
sured cases), a Ch Ch Ch (triplet) in four groups (14.8 %
of measured cases), and a Ch Ch Ch Ch (quadruplet) in
one group (0.01 % of measured cases). Only four groups
at Villa Carmen exhibited a triplet Ch Ch, and a group at
CREES produced the call in a quadruplet. e Long Trill is
named in part after the Trill described originally by Andrew
(1963), though structurally there are dierences. Namely,
in our study the call descends in frequency, whereas there is
an oscillation around 3,500-5,000Hz in A. lemurinus. e
Long Trill is also found primarily between 3,500-5,000HZ,
whereas our study had a higher frequency around 3,000HZ.
ere were several instances of the Long Trill, but only in two
groups found at Villa Carmen Biological Station. However,
only a single instance had a clear spectrogram that could be
used for analysis due to the complexity of the acoustic land-
scape at that particular frequency.
Neotropical Primates 24(1), June 2018 33
No known studies have assessed the bioacoustics of any wild
Aotus species. Furthermore, no studies have analyzed Ao-
tus nigriceps vocalizations, even in captivity. is study de-
scribes three calls in A. nigriceps (Twitter, Ch Ch, and Long
Trill), though continued eld research may reveal additional
calls. irteen other calls have previously been described in
A. azarae and A. lemurinus, which suggests that the vocal
repertoire of Aotus nigriceps is likely larger than described
here. However, captive settings allow researchers to control
for background noise and to elicit calls in response to ex-
perimental stimuli, which may increase the number of calls
found in captivity compared to a wild setting. Bioacoustic
information in wild primates is also likely to be dierent
than those in captivity because of their capacity to adjust
calls in an environment lled with background white noise
from both biotic and abiotic factors (Brumm et al. 2004).
For example, the frequency range of captive Aotus species
was previously reported to be 140-5,800 Hz; however, some
of our calls peaked at 13,612 Hz (e.g., Ch Ch), and all but
one call fell within the previously reported range. is could
be an adaptation to a much more crowded acoustic envi-
ronment, where other organisms use a similar bandwidth
(Ey and Fischer 2009). We report initial ndings of behav-
ioral associations with vocalizations, though caution must
be taken in interpreting these results since the majority of
behaviors couldn’t be documented due to dense foliage or
total darkness. Our continued research includes aspects of
intra- and inter-group variability, geographic variability, in-
ter-species diversity, and behavioral playback experiments in
wild Aotus nigriceps populations.
ank you to the Amazon Conservation Association
(ACA), Villa Carmen Biological Station and Manu Learn-
ing Center (CREES) sta for hosting us, clearing trails,
and providing valuable insight into location and behavior
of groups. We are indebted to students and sta from the
School for Field Studies who assisted with data collection
and logistics.
William Daniel Helenbrook, State University of New
York College of Environmental Science and Forestry
(SUNY-ESF), Syracuse, New York and Tropical Conser-
vation Fund, Atlanta, Georgia; Email: <wdhelenb@syr.
edu>; Leigh Preston, Hamilton College, Clinton, New
York; Noah Alexander Linck, University of Minnesota
Twin-Cities, St. Paul, Minnesota; Megan Quirk, Gustavus
Adolphus College, St. Peter, Minnesota; Jessica Alexandra
Suarez, Tropical Conservation Fund, Atlanta, Georgia.
Andrew, R. J. 1963. Origin and evolution of the calls and
facial expressions of the primates. Behaviour 20: 1–109.
Brumm, H., K. Voss, I, Kollmer, and D. Todt. 2004.
Acoustic communication in noise: regulation of calls
characteristics in a New World monkey. J. Exp. Biol. 207:
Ey, E., and J. Fischer. 2009. e “acoustic adaptation hy-
pothesis”—a review of the evidence from birds, anurans
and mammals. Bioacoustics 19: 21–48.
Moynihan, M. 1964. Some behavior patterns of platyr-
rhine monkeys. I. e night monkeys (Aotus trivirgatus).
Smithson. Misc. Collect. 146: 1–84.
Salmi, R., K. Hammerschmidt, and D. Doran-Sheehy.
2014. Individual distinctiveness in call types of wild
western female gorillas. PLoS ONE 9: 1–13.
Sri Kantha, S., H. Koda, and J. Suzuki. 2009. Owl monkey
vocalizations at the primate research institute, Inuyama.
Neotrop. Primates 16: 43–46.
Breno Dias Vitorino
Angélica Vilas Boas da Frota
Solange Kimie Ikeda Castrillon
e black titi monkey, previously classied as Callicebus cin-
erascens (Spix, 1823), from molecular evidence is currently
included in the genus Plecturocebus (Byrne et al., 2016).
Has a gray coat over almost all the body with a contrasting
brown patch on the back. It feeds on fruits, leaves, insect
and seeds. It inhabits dry land environments, Campinara-
na (forest fragments with poor, rocky, shallow soil and a
mix of trees and bamboo), secondary forests and relatively
open areas. Its known distribution is still imprecise due to
the limited number of records for the species (Veiga et al.,
2008). Current knowledge about Plecturocebus cinerascens
distribution indicates occurrence in the Madeira-Tapajós
interuves (Noronha et al., 2007), with records on the left
bank of the Juruena River, the region of the headwaters of
the Roosevelt River, the right bank of the Cabixi River, the
right bank of the Alto Guaporé River among municipality
of Vila Bela da Santíssima Trindade and Pontes e Lacerda,
and within the Juruena-Teles Pires interuves (Sampaio et
al., 2012). e western limit may be the municipality of
Pimenteiras do Oeste, in the middle of the Vale do Gua-
poré, in the state of Rondônia, Brazil (Gusmão and Costa,
2014). e species is considered endemic to Brazil.
For this poorly known species (Sampaio et al., 2012) with
an imprecise distribution delimitation especially in relation
to its southern and southeastern limits (Veiga et al., 2008),
new record reports are extremely important. e present
study presents four new observations of P. cinerascens in the
... Accordingly, it could be expected that acoustic communication should be equally important for the only extant American primates with nocturnal habits (the night monkey: genus Aotus). However, only a few studies regarding acoustic communication in night monkeys have been conducted (Andrew, 1963;Moynihan, 1964;Wright, 1978Wright, , 1985Depeine, 2008;Kantha et al., 2009;Helenbrook et al., 2018Helenbrook et al., , 2019Garcia de la Chica et al., 2020. ...
... azarae), Kantha et al. (2009) reported six different vocalizations for captive individuals. Finally, Helenbrook et al. (2018) recently suggested that wild Blackheaded night monkey (A. nigriceps) had at least three different vocalization types. ...
... Based on an initial auditory and visual inspection of the spectrograms, we made an initial classification of all vocalizations recorded during the study. We named the different types of vocalizations based on their onomatopoeic sound, as well as on earlier descriptions of vocalizations made by night monkeys in previous studies (Andrew, 1963;Moynihan, 1964;Kantha et al., 2009;Helenbrook et al., 2018). We then selected the best recordings (good signal to noise ratio) of each vocalization for bioacoustics analyses. ...
Vocal communication is particularly important for nocturnal species as well as those living in dense forests, where visual abilities can be somewhat constrained. The Andean night monkey (Aotus lemurinus) is a nocturnal American primate living in mountain forests in the Northern Andes with scant information on its behavior and ecology. The main goal of this study is to describe the vocal repertoire of a group of wild Andean night monkeys and compare it with earlier bioacoustics studies on the only nocturnal platyrrhines. We recorded the vocal behavior of a group of night monkeys living in the eastern Andes of Colombia between August and December 2019. Based on an auditory and a visual inspection of the vocal records, and through a quantitative analysis of the acoustic parameters of the vocalizations, we were able to identify five different calls emitted by the Andean night monkey. Four of these calls are stereotyped while the fifth vocalization (Squeak) is more variable, having different forms. Additionally, one call (Acetate) was found to be unique to this species. The result of this study contributes to the scant information on the ecology and behavior of the Andean night monkey and sets baseline information on the vocal behavior of night monkeys that may be used in future studies on communication of these and other nocturnal primates.
... In contrast to other genera, our knowledge of owl monkey vocal communication that would allow evaluation of the hypothesis remains quite limited. Only two studies on captive animals have assessed the vocal repertoire of Aotus (Moynihan 1964;Kantha et al. 2009); in two other studies of vocal communication in wild owl monkeys, the authors were not able to unequivocally identify the sexes or age of the individuals due to the strictly nocturnal habits of the species studied (Wright 1985;Helenbrook et al. 2018). These studies suggested that one call, the hoot call, conveys information over long distances and that could be differentiated into two sub-types, graff and tonal ones (Wright 1985). ...
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Primates use different types of vocalizations in a variety of contexts. Some of the most studied types have been the long distance or loud calls. These vocalizations have been associated with mate defense, mate attraction, and resource defense, and it is plausible that sexual selection has played an important role in their evolution. Focusing on identified individuals of known sex and age, we evaluated the sexual dimorphism in a type of loud calls (hoots) in a population of wild owl monkeys (Aotus azarae) in Argentina. We found evidence of sexual dimorphism in call structure, with females and males only emitting one type of call, each differing in dominant frequency and Shannon entropy. In addition, both age-related and sex-specific differences in call usage were also apparent in response to the removal of one group member. Future acoustic data will allow us to assess if there are individual characteristics and if the structure of hoot calls presents differences in relation to the social condition of owl monkeys or specific sex responses to variants of hoot calls’ traits. This will provide deeper insights into the evolution of vocal mechanisms regulating pair bonding and mate choice strategies in this and other primate species.
Although studying communication among nocturnal primates is particularly challenging, decades of research provide sufficient evidence to recognize that communication between owl monkey pair mates, among group members, and with individuals outside of the group is based on a variety of visual, tactile, auditory, and olfactory signals. Owl monkeys have evolved specialized morphology to facilitate communication, including a vocal sac and well-developed glandular regions used in scent-marking. Several aspects of communication also show some degree of dimorphism, particularly vocalizations, chemical deposits, and glandular morphology. Communication within the group may facilitate cohesion, coordination, travel, maintenance of the pair-bond, and development of relationships between adults and their young, possibly also mediating dispersal behavior. On the other hand, communication with individuals outside of the group, accomplished through indirect vocal and olfactory signals, or direct signals when visual and/or physical contact with neighboring groups or floaters occur, may aid in mate attraction or home range defense.
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Individually distinct vocalizations play an important role in animal communication, allowing call recipients to respond differentially based on caller identity. However, which of the many calls in a species' repertoire should have more acoustic variability and be more recognizable is less apparent. One proposed hypothesis is that calls used over long distances should be more distinct because visual cues are not available to identify the caller. An alternative hypothesis proposes that close calls should be more recognizable because of their importance in social interactions. To examine which hypothesis garners more support, the acoustic variation and individual distinctiveness of eight call types of six wild western gorilla (Gorilla gorilla) females were investigated. Acoustic recordings of gorilla calls were collected at the Mondika Research Center (Republic of Congo). Acoustic variability was high in all gorilla calls. Similar high inter-individual variation and potential for identity coding (PIC) was found for all call types. Discriminant function analyses confirmed that all call types were individually distinct (although for call types with lowest sample size - hum, grumble and scream - this result cannot be generalized), suggesting that neither the distance at which communication occurs nor the call social function alone can explain the evolution of identity signaling in western gorilla communication.
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Quantitative evaluations of vocalizations of nocturnally active owl monkeys (Aotus species) have been attempted only twice. Andrew (1963) identified four call types in 2 captive individuals. Moynihan (1964) identified six call types in a quasi-wild condition. We studied vocalizations of 16 owl monkeys (Aotus azarae) reared at the Kyoto University's Primate Research Institute facility, under captive conditions. We could distinguish six categories of acoustic call types. These were, moan, long scream, gulp, low trill, short scream and sneeze grunt. During the recording period, low trill was the most frequent and sneeze grunt was the least frequent call. Sound spectrograms of six call types recorded are provided.
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The acoustic properties of the environment influence sound propagation. Many previous studies examined whether various species of anurans, birds and mammals adjust usage and/or structure of their vocal signals to limit degradation during propagation in this environment (“acoustic adaptation hypothesis”). The present review examines how widespread such adaptations actually are across taxa. First, evidence for environment-related adjustments in usage of vocal signals is collected from studies in birds and other vertebrates (i.e., anurans and mammals). Second, a meta-analysis conducted by Boncoraglio & Saino (2007) on the influences of the environment on the acoustic structure of avian vocalisations is taken as a reference, and results from additional studies in birds are reviewed and compared to its conclusions. Finally, evidence from similar studies conducted in anurans and mammals is collected and discussed. Concerning the usage of vocal signals, evidence of environment-related adaptations in the few studies found was more widespread in anurans and mammals than in birds. Regarding structure of vocal signals, evidence from additional studies in birds did not completely confirm results of the meta-analysis of Boncoraglio & Saino (2007). Pooling all bird studies together presented minimum frequency, frequency modulations and frequency range as acoustic variables most often adjusted to the environment, in contrast to temporal features, repetition rate and maximum frequency. The few studies conducted in anurans and mammals did not allow the identification of specific acoustic variables that typically show environment-related variations. Overall, evidence for the acoustic adaptation hypothesis was not as widespread as expected across taxa. The different aspects of vocal behaviour adapted to environmental conditions varied according to the species and local habitats. Environment-related adjustments in structure of vocal signals seem to be constrained by call function in anurans and mammals. This effect was not examined in birds, but vocal learning does not appear to be a pre-requisite to environment-related adjustment in this group.
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This study on common marmosets Callithrix jacchus is the first to examine noise-dependent mechanisms of vocal plasticity in a New World monkey. Since acoustic communication can be considerably impaired by environmental noise, some animals have evolved adaptations to counteract its masking effects. The studied marmosets increased the sound level of their spontaneous calls in response to increased levels of white noise broadcast to them. Possibly, such noise-dependent adjustment of vocal amplitude serves to maintain a specific signal-to-noise ratio that is favourable for signal production. Concurrently, the adjustment of vocal amplitude can maintain a given active space for communication. In contrast to some bird species, no noise-induced increase in the number of syllables per call series could be found, showing that an increased serial redundancy of vocal signals was not used to communicate under noisy conditions. Finally, we examined a possible noise-dependent prolongation of vocal signals. This approach was guided by the findings of perceptional studies, which suggest an increased detection probability of prolonged signals in noise by temporal summation. Marmosets indeed increased the duration of their call syllables along with increasing background noise levels. This is the first evidence of such mechanism of vocal plasticity in an animal communication system.
This is the first in a series of papers on some behavior patterns of New World monkeys. The main emphasis of these papers will be comparative. Special attention will be paid to social signal patterns (including hostile and sexual signals) and other patterns that differ significantly in the various species. It is hoped that analyses of these patterns may throw some light on the evolution of the group as a whole.
1. It is not possible to treat mammalian vocalisations and facial expressions in terms of a drive model. They can be best described as basically dependent on