The Vocal Repertoire of Adult and Neonate Giant Otters (Pteronura brasiliensis)
Citation: Mumm CAS, Kno rnschild M (
The Vocal Repertoire of Adult and Neonate Giant Otters (Pteronura brasiliensis )
Christina A. S. Mumm 0
Mirjam Kno rnschild 0
Dennis M. Higgs, University of Windsor, Canada
0 1 Institute of Experimental Ecology, University of Ulm , Ulm, Germany , 2 Institute of Experimental Ecology, Faculty of Natural Sciences, University of Ulm , Ulm, Germany , 3 Smithsonian Tropical Research Institute , Balboa , Panama
Animals use vocalizations to exchange information about external events, their own physical or motivational state, or about individuality and social affiliation. Infant babbling can enhance the development of the full adult vocal repertoire by providing ample opportunity for practice. Giant otters are very social and frequently vocalizing animals. They live in highly cohesive groups, generally including a reproductive pair and their offspring born in different years. This basic social structure may vary in the degree of relatedness of the group members. Individuals engage in shared group activities and different social roles and thus, the social organization of giant otters provides a basis for complex and long-term individual relationships. We recorded and analysed the vocalizations of adult and neonate giant otters from wild and captive groups. We classified the adult vocalizations according to their acoustic structure, and described their main behavioural context. Additionally, we present the first description of vocalizations uttered in babbling bouts of new born giant otters. We expected to find 1) a sophisticated vocal repertoire that would reflect the species' complex social organisation, 2) that giant otter vocalizations have a clear relationship between signal structure and function, and 3) that the vocal repertoire of new born giant otters would comprise age-specific vocalizations as well as precursors of the adult repertoire. We found a vocal repertoire with 22 distinct vocalization types produced by adults and 11 vocalization types within the babbling bouts of the neonates. A comparison within the otter subfamily suggests a relation between vocal and social complexity, with the giant otters being the socially and vocally most complex species.
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Competing Interests: The authors have declared that no competing interests exist.
The complexity of mammalian vocal repertoires is both the sum
of several aspects of call structure and function, as well as of
evolutionary and selective pressures acting on senders and
receivers. Production and perception mechanisms, such as the
anatomic structure of the vocal tract or auditory sensitivity, shape
and limit the number of distinct vocalizations a species can
produce and perceive [14]. As described by the source-filter
theory [5,6], source (i.e. larynx) induced acoustic parameters
include duration, tempo, fundamental frequency and nonlinear
phenomena [7,8]. Nonlinear phenomena, being subharmonics,
biphonation and deterministic chaos [8], seem to be a rather
involuntary by-product of vocal production, nevertheless,
increasing the diversity of acoustic signals [9]. Filter (i.e. supralaryngeal
vocal tract) induced vocal parameters include formants which,
among other cues, indicate the body size of the signaller [10].
Vocalizations can be internally referential, providing
information on motivational state, individuality or social origin of the
sender, or externally referential, providing information on external
events for receivers [1]. According to Mortons
motivationstructural rules [11], the physical structure of mammalian and
avian vocal signals reflects the motivation and context in which
they are produced. Aggressive vocalizations should have lower
frequencies and sound harsh, whereas friendly calls should have
higher frequencies and sound pure [11]. Bradbury and
Vehrencamp [12] refined these motivation-structural rules for the design
of mate-attracting, courtship, territorial defence, threat and alarm
signals.
The vocalizations within many mammalian repertoires are
neither completely discrete, nor completely graded [13,14]. They
rather represent a combination of distinct calls, graded signals,
variants, and transitions between them [12,15,16]. By varying
certain acoustic parameters, animals can use variants of graded
vocalizations to signal a more detailed information about their
internal state, motivation, or the degree of external danger [12].
Segmental concatenation, being the combination of different vocal
cues in one call type [17], as well as a structured combination of
vocalizations, resulting in a different or more specific meaning
than that of single calls, contribute to the enhancement of a vocal
repertoire [1820].
Cognitively advanced mammals such as primates do not only
perceive and recognize distinct meaning from graded call subtypes
[18], but may respond differently to apparently similar calls, or,
conversely, may be able to derive the same meaning from
structurally different vocalizations [21]. Thi (...truncated)