Because whistles are most commonly associated with social delphinids, they have been largely overlooked, ignored, or presumed absent, in solitary freshwater dolphin species. Whistle production in the freshwater dolphin, the boto (Inia geoffrensis geoffrensis), has been controversial. Because of its sympatry with tucuxi dolphins (Sotalia fluviatilis), a whistling species, some presume tucuxi whistles might have been erroneously assigned to the boto. Using a broadband recording system, we recorded over 100 whistles from boto dolphins in the Yasuní River, Ecuador, where the tucuxi dolphins are absent. Our results therefore provide conclusive evidence for whistle production in Inia geoffrensis geoffrensis. Furthermore, boto whistles are significantly different from tucuxi whistles recorded in nearby rivers. The Ecuadorian boto whistle has a significantly greater frequency range (5.3048.10kHz) than previously reported in other populations (Peru and Colombia) that were recorded with more bandwidth limited equipment. In addition, the top frequency and the range are greater than in any other toothed whale species recorded to date. Whistle production was higher during resting activities, alone or in the presence of other animals. The confirmation of whistles in the boto has important implications for the evolution of whistles in Cetacea and their association with sociality.

1.
Aliaga-Rossel
,
E.
(
2002
). “
Distribution and abundance of the river dolphin (Inia geoffrensis) in the Tijamuchi River, Beni, Bolivia
,”
Aquat. Mamm.
28
,
312
323
.
2.
Azevedo
,
A. F.
, and
Van Sluys
,
M.
(
2005
). “
Whistles of tucuxi dolphins (Sotalia fluviatilis) in Brazil: Comparisons among populations
,”
J. Acoust. Soc. Am.
117
,
1456
1464
.
3.
Azevedo
,
A. F.
, and
Simão
,
S. M.
(
2002
). “
Whistles produced by marine tucuxi dolphins Sotalia fluviatilis in Guanabara Bay, southeastern Brazil
,”
Aquat. Mamm.
28
,
261
266
.
4.
Au
,
W. W. L.
(
2000
). “
Hearing in whales and dolphins: An overview
,” in
Hearing by Whales and Dolphins
, edited by
W. W. L.
Au
,
A. N.
Popper
, and
R. R.
Fay
(
Springer-Verlag
,
New York
), pp.
1
42
.
5.
Barzúa-Durán
,
M. C.
, and
Au
,
W. W. L.
(
2002
). “
Whistles of Hawaiian spinner dolphins
,”
J. Acoust. Soc. Am.
112
,
3064
3072
.
6.
Barzúa-Durán
,
M. C.
(
2004
). “
Differences in the whistle characteristics and repertoire of bottlenose and spinner dolphins
,”
An. Acad. Bras. Cienc.
76
,
386
392
.
7.
Barzúa-Durán
,
M. C.
, and
Au
,
W. W. L.
(
2004
). “
Geographic variations in the whistles of spinner dolphins (Stenella longirostris) of the Main Hawaiian Islands
,”
J. Acoust. Soc. Am.
116
,
3757
3769
.
8.
Belikov
,
R. A.
, and
Bel’kovich
,
V. M.
(
2001
). “
Characteristics of white sea beluga whale (Delphinapterus leucas) whistle-like signals
,”
XI Session of the Russian Acoustical Society
,
Moscow
, November 19–23.
9.
Belikov
,
R. A.
, and
Bel’kovich
,
V. M.
(
2003
). “
Underwater vocalization of the beluga whales (Delphinapterus leucas) in a reproductive gathering in various behavioral situations
,”
Oecologia
43
,
112
120
.
10.
Best
,
R. C.
, and
da Silva
,
V. M. F.
(
1993
). “
Inia geoffrensis
,”
Mammalian Species
426
,
1
8
.
11.
Boisseau
,
O.
(
2005
). “
Quantifying the acoustic repertoire of a population: The vocalizations of free-ranging bottlenose dolphins in Fiordland, New Zealand
,”
J. Acoust. Soc. Am.
117
,
2318
2329
.
12.
Caldwell
,
M. C.
, and
Caldwell
,
D. K.
(
1965
). “
Individual whistle contours in bottlenose dolphins (Tursiops truncatus)
,”
Nature (London)
207
,
434
435
.
13.
Caldwell
,
M. C.
, and
Caldwell
,
D. K.
(
1967
). “
Intra-specific transfer of information via the pulsed sound in captive odontocete cetaceans
,” in
Animal Sonar Systems
, edited by
R.-G.
Busnel
(
Jouy-en-Josas
,
France
), Vol.
2
, pp.
879
936
.
14.
Caldwell
,
M. C.
,
Caldwell
,
D. K.
, and
Evans
,
W. E.
(
1966
). “
Sounds and behavior of captive Amazon freshwater dolphin, Inia geoffrensis
,”
Los Angeles County Mus. Cont. Sci.
108
,
1
24
.
15.
Caldwell
,
M. C.
,
Caldwell
,
D. K.
, and
Tyack
,
P. L.
(
1990
). “
Review of the signature-whistle hypothesis for the Atlantic bottlenose dolphin
,” in
The Bottlenose Dolphin
, edited by
S.
Leatherwood
and
R. R.
Reeves
(
Academic
,
San Diego
), pp.
199
234
.
16.
da Silva
,
V. M. F.
(
2002
). “
Amazon River dolphin (Inia geoffrensis)
,” in
Encyclopedia of Marine Mammals
, edited by
W. F.
Perrin
,
B.
Wursig
, and
J. G. M.
Thewissen
(
Academic
,
San Diego
), pp.
18
20
.
17.
Dawson
,
S.
,
Barlow
,
J.
, and
Ljungbland
,
D.
(
1998
). “
Sounds recorded from Baird’s beaked whale, Berardius bairdii
,”
Marine Mammal Sci.
14
,
335
344
.
18.
Dekinger
,
J.
(
2001
). “
Demographische untersuchunge am Amazonasdelphin (Inia geoffrensis) in cuyabeno reseervat, in Ecuador
,” Ph.D. Dissertation,
Universitat Bielefeld
, Bielefeld, Germany.
19.
Diazgranados
,
M. C.
, and
Trujillo
,
F.
(
2002
). “
Vocal repertoire of the freshwater dolphins Inia geoffrensis and Sotalia fluviatilis in Colombia, South America
,”
J. Acoust. Soc. Am.
112
,
2400
.
20.
Fletcher
,
N. H.
(
1992
).
Acoustic Systems in Biology
,
Oxford University Press
,
Oxford, England
, p.
352
.
21.
Ford
,
J. K. B.
, and
Fisher
,
H. D.
(
1978
). “
Underwater acoustic signals of the narwhal (Monodon monocerus)
,”
Can. J. Zool.
56
,
552
560
.
22.
Fripp
,
D.
,
Owen
,
C.
,
Quintana-Rizzo
,
E.
,
Shapiro
,
A.
,
Buckstaff
,
K.
,
Jankowski
,
K.
,
Wells
,
R.
, and
Tyack
,
P.
(
2005
). “
Bottlenose dolphin (Tursiops truncatus) calves appear to model their signature whistles on the signature whistles of community members
,”
Anim. Cogn.
8
,
17
26
.
23.
Galacatos
,
K.
,
Barriga-Salazar
,
R.
, and
Steward
,
D. J.
(
2004
). “
Seasonal and habitat influences on fish communities within the lower Yasuní River Basin of the Ecuatorian Amazon
,”
Environ. Biol. Fishes.
71
,
33
51
.
24.
Hamilton
,
H.
,
Caballeron
,
S.
,
Collins
,
A. G.
, and
Brownell
, Jr.,
R. L.
(
2001
). “
Evolution of river dolphins
,”
Proc. R. Soc. London, Ser. B
268
,
549
558
.
25.
Herman
,
L. M.
, and
Tavolga
,
W. N.
(
1980
). “
The communication systems of cetaceans
,” in
Cetacean Behavior: Mechanisms and Functions
, edited by
L. M.
Herman
(
Wiley
,
New York
).
26.
Herzing
,
D. L.
(
2000
). “
Acoustics and social behavior of wild dolphins: Implications for a sound society
,” in
Hearing by Whales and Dolphins
, edited by
W. W. L.
Au
,
A. N.
Popper
, and
R. E.
Fay
(
Springer
,
New York
), pp.
225
272
.
27.
Janik
,
V. M.
(
2000
). “
Whistle matching in wild bottlenose dolphins (Tursiops truncatus)
,”
Science
289
,
1355
1357
.
28.
Jing
,
X.
,
Xiao
,
Y.
, and
Jing
,
R.
(
1981
). “
Acoustic signals and acoustic behavior of Chinese river dolphin (Lipotes vexillifer)
,”
Sci. Sin.
2
,
233
239
.
29.
Jones
,
G. J.
, and
Sayigh
,
L. S.
(
2002
). “
Geographic variation in rates of vocal production of free-ranging bottlenose dolphins
,”
Marine Mammal Sci.
18
,
384
393
.
30.
Karlsen
,
J. D.
,
Bisther
,
A.
,
Lydersen
,
C.
,
Haug
,
T.
, and
Kovacs
,
K. M.
(
2002
). “
Summer vocalizations of adult male white whales (Delphinapterus leucas) in Svalbard, Norway
,”
Polar Biol.
25
,
808
817
.
31.
Lammers
,
M. O.
, and
Au
,
W. W. L.
(
2003
). “
Directionality in the whistles of Hawaiian spinner dolphins (Stenella longirostris): A signal feature to cue direction of movement
?”
Marine Mammal Sci.
19
,
249
264
.
32.
LeDuc
,
R. G.
,
Perrin
,
W. F.
, and
Dizon
,
A. E.
(
1999
). “
Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences
,”
Marine Mammal Sci.
15
,
619
648
.
33.
Marquet
,
P. O.
, and
Taper
,
M. L.
(
1998
). “
On size and area: Patterns of mammalian body size extreme across landmasses
,”
Evol. Biol.
12
,
127
139
.
34.
Matthews
,
J. N.
,
Rendell
,
L. E.
,
Gordon
,
J. C. D.
, and
MacDonald
,
D. W.
(
1999
). “
A review of frequency and time parameters of cetacean tonal calls
,”
Bioacoustics
10
,
47
71
.
35.
May-Collado
,
L. J.
, and
Agnarsson
,
I.
(
2006
). “
Cytochrome b and Bayesian inference of whale phylogeny
,”
Mol. Phylogenet. Evol.
38
,
344
354
.
36.
May-Collado
,
L. J.
,
Agnarsson
,
I.
, and
Wartzok
,
D.
(
2006
). (in press) “Reexamining the relationship between body size and tonal signals frequency in whales: A comparative phylogenetic approach,” Marine Mammal Science.
37.
May-Collado
,
L. J.
,
Agnarsson
,
I.
, and
Wartzok
,
D.
(
2006
). (B) “
Phylogenetic review of tonal sound production in whales in relation to sociality
,” (Submitted to BMC Evol. Biol.)
38.
McGuire
,
T. L.
, and
Winemiller
,
K. O.
(
1998
). “
Ocurrence patterns, habitat associations, and potential prey of the river dolphin, Inia geoffrensis, in the Cinaruco River, Venezuela
,”
Biotropica.
30
,
625
638
.
39.
Monteiro-Filho
,
E. L. A.
(
2000
). “
Group organization of the dolphin Sotalia fluviatilis guianensis in an estuary of southeastern Brazil
,”
Ciencia e Cultura J. Braz. Ass. Adv. Sci.
52
,
97
101
.
40.
Morisaka
,
T.
,
Shinohara
,
M.
,
Nakahara
,
F.
, and
Akamatsu
,
T.
(
2005a
). “
Geographic variations in the whistles among three Indo-Pacific bottlenose dolphin Tursiops aduncus populations in Japan
,”
Fish. Sci.
71
,
568
576
.
41.
Morisaka
,
T.
,
Shinohara
,
M.
,
Nakahara
,
F.
, and
Akamatsu
,
T.
(
2005b
). “
Effects of ambient noise in the whistles of Indo-Pacific bottlenose dolphin Tursiops aduncus populations in Japan
,”
J. Mammal.
86
,
541
546
.
42.
Nakasai
,
K.
, and
Takemura
,
A.
(
1975
). “
Studies on the underwater sound. VI. On the underwater calls of freshwater dolphins in South America
,”
Bull. Fac. Fish. Nagasaki Univ.
40
,
7
13
.
43.
Oswald
,
J. N.
,
Rankin
,
S.
, and
Barlow
,
J.
(
2004
). “
The effect of recording and analysis bandwidth on acoustic identification of delphinid species
,”
J. Acoust. Soc. Am.
116
,
3178
3185
.
44.
Podos
,
J.
,
da Silva
,
V. M. F.
, and
Rossi-Santos
,
M. R.
(
2002
). “
Vocalizations of Amazon river dolphins, Inia geoffrensis: Insights into the evolutionary origins of delphinid whistles
,”
Ethology
108
,
601
612
.
45.
Quintana-Rizzo
,
E.
,
Mann
,
D. A.
, and
Wells
,
R. S.
(
2006
). “
Estimated communication range of social sounds used by bottlenose dolphins (Tursiops truncatus)
,”
J. Acoust. Soc. Am.
120
,
1671
1683
.
46.
Rasmussen
,
M. H.
, and
Miller
,
L. A.
(
2002
). “
Whistles and clicks from white-beaked dolphins (Lagenorhynchus albirostris Gray 1846), recorded in Faxafloi Bay, Iceland
,”
Aquat. Mamm.
28
,
78
89
.
47.
Rasmussen
,
M. H.
,
Lammers
,
M.
,
Beedholm
,
K.
, and
Miller
,
L. A.
(
2006
). “
Source levels and harmonic content of whistles in white-beaked dolphins (Lagenorhynchus albirostris)
,”
J. Acoust. Soc. Am.
120
,
511
517
.
48.
Richardson
,
W. J.
,
Greene
,
C. R. J.
,
Malme
,
C. I.
, and
Thomsom
,
D. H.
(
1995
).
Marine Mammals and Noise
(
Academic
,
New York
), p.
547
.
49.
Rogers
,
T. L.
, and
Brown
,
S. M.
(
1999
). “
Acoustic observations of Arnoux’s beaked whale (Berardius arnuxii) off Kemp Land, Antarctica
,”
Marine Mammal Sci.
15
,
192
198
.
50.
Rossi-Santos
,
M. R.
, and
Podos
,
J.
(
2006
). “
Latitudinal variation in whistle structure of the estuarine dolphin Sotalia guianensis
,”
Behaviour
143
,
347
364
.
51.
Sætre
,
G. P.
,
Moum
,
T.
,
Bures
,
S.
,
Kral
,
M.
,
Adamjan
,
M.
, and
Moreno
,
J.
(
1997
). “
A sexually selected character displacement in flycatchers reinforces premating isolation
,”
Nature (London)
387
,
589
591
.
52.
Shapiro
,
A.
(
2006
). “
Preliminary evidence for signature vocalizations among free-ranging narwhals (Monodon monocerus)
,”
J. Acoust. Soc. Am.
120
,
1695
1705
.
53.
Sjare
,
B. L.
, and
Smith
,
T. G.
(
1986
). “
The vocal repertoire of white whales, Delphinapterus leucas, summering in Cunningham Inlet, Northwest Territories
,”
Can. J. Zool.
64
,
407
415
.
54.
Steiner
,
W. W.
(
1981
). “
Species-specific differences in pure tonal whistle vocalizations of five western North Atlantic dolphin species
,”
Behav. Ecol. Sociobiol.
9
,
241
246
.
55.
Tyack
,
P. L.
(
1997
). “
Development and social functions of signature whistles in bottlenose dolphins Tursiops truncatus
,”
Bioacoustics
8
,
21
46
.
56.
Tyack
,
P. L.
(
2000
). “
Functional aspects of cetacean communication
,” in
Cetacean Societies: Field Studies of Dolphins and Whales
, edited by
J.
Mann
,
R. C.
Connor
,
P. L.
Tyack
, and
H.
Whitehead
(
The University of Chicago Press
,
Chicago
), pp.
270
307
.
57.
Van Parijs
,
S. M.
, and
Corkeron
,
P. J.
(
2001
). “
Vocalizations and behaviour of Pacific Humbpaback dolphins, Sousa chinensis
,”
Ethology
107
,
701
716
.
58.
Wang
,
D.
,
Lu
,
W.
, and
Wang
,
K.
(
1989
). “
A preliminary study of the acoustic behavior of the baiji, Lipotes vexillifer
,”
Occasional Papers of the IUCN Species Survival Commission (SSC) No. 3
, pp.
137
140
.
59.
Wang
,
D.
,
Würsig
,
B.
, and
Evans
,
W. E.
(
1995a
). “
Comparisons of whistles among seven odontocete species
,” in
Sensory Systems of Aquatic Mammals
, edited by
R. A.
Kastelien
,
J. A.
Thomas
, and
P. E.
Nachtigal
(
De Spill
,
Woerden, The Netherlands
) pp.
299
323
.
60.
Wang
,
D.
,
Wursig
,
B.
, and
Evans
,
W. E.
(
1995b
). “
Whistles of bottlenose dolphins: Comparisons among populations
,”
Aquat. Mamm.
21
,
65
77
.
61.
Wang
,
D.
,
Würsig
,
B.
, and
Leatherwwod
,
S.
(
2001
). “
Whistles of boto, Inia geoffrensis, and tucuxi, Sotalia fluviatilis
,”
J. Acoust. Soc. Am.
109
,
407
414
.
62.
Wang
,
X.
,
Wang
,
D.
,
Akamatsu
,
T.
,
Fujita
,
K.
, and
Shiraki
,
R.
(
2006
). “
Estimated detection distance of a baiji’s (Chinese river dolphin, Lipotes vexillifer) whistles using a passive acoustic survey method
,”
J. Acoust. Soc. Am.
120
,
1361
1365
.
63.
Watkins
,
W. A.
,
Schevill
,
W. E.
, and
Ray
,
C.
(
1970
). “
Underwater sounds of Monodon (Narwhal)
,”
J. Acoust. Soc. Am.
49
,
595
599
.
64.
Watwood
,
S. L.
,
Tyack
,
P. L.
, and
Wells
,
R. S.
(
2004
). “
Whistle sharing in paired male bottlenose dolphins, Tursiops truncatus
,”
Behav. Ecol. Sociobiol.
55
,
531
543
.
65.
Xianying
,
J.
,
Youfo
,
X.
, and
Rongcai
,
J.
(
1981
). “
Acoustic signals and acoustic behavior of the Chinese River Dolphin (Lipotes vexillifer)
,”
Sci. Sin.
24
,
407
415
.
66.
Zapata-Rios
,
G.
, and
Utreras
,
V. B.
(
2004
). “
Notes on the distribution of tucuxi, Sotalia fluviatilis (Cetacea: Delphinidae), in Ecuadorian Amazonia
,”
Lat. Am. J. Aquatic Mamm.
3
,
85
87
.
You do not currently have access to this content.