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ISSN 0889-3667
IJCP8 12(3)111-179(1999)




Published by

The International Society


Comparative Psychology



Lesley J. Rogers

Division of Zoology

School of Biological Sciences

University of New England

Armidale NSW 2351


Sally A. McFadden
Dept. of Psychology
Faculty of Science and Maths
The University of Newcastle
NSW 2308


Ruben Ardila
University of Colombia
Apartado 88754
Bogota Colombia S.A.

Juan D. Delius
AUgemaine Psychologie
Universitat Konstanz
D-78434 Konstanz 1

Jack Demarest
Department of Psychology
Monmouth University
West Long Branch
NJ 07764, USA

Gordon G. Gallup Jr
Department of Psychology
SUNY at Albany
Albany, NY 12222 USA

Gary Greenberg
Dept. of Psychology
Wichita State University
Wichita, Kansas
67260-0034 USA

R. Bryan Jones
Roslin Institute
(Edinburgh), Roslin
Midlothian EH25 9PS

Peter Klopfer
Department of Zoology
Duke University, Durham
NC 27706 USA

Mauricio R. Papini*
Department of Psychology
Texas Christian University
Fort Worth, TX 76129 USA

Wojciech Pisula
Faculty of Psychology
University of Warsaw,
Stawki 5/7
00-183 Warsaw POLAND

Emanuela Prato Previde
Istituto di Psicologia della
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Universita di Milano, via T.
Pini 1
20134 Milano, ITALY

Michael Renner
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West Chester University,
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University of Fort Hare
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Roger K. Thomas

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The University of Georgia,


GA 30602-3013, USA

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American Museum of

Natural History

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New York 10024-5192,


Dora F. Ventura
Instituto de Psicologia
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Jeannette P. Ward
Department of Psychology
The University of Memphis
Memphis, TN 38152 USA

* Please note that the current Editors are retiring and Dr Mauricio Papini (address
above) will be the the new Editor. Manuscripts should be submitted directly to Dr


Volume 12, Number 3, 1999

The Function and Significance of Inter-species
Acoustic Cues in the Transformation of Budgerigar
{Melopsittacus Undulatus) Sounds Into "Speech"

Jim Scanlan 111

Decision Making and Turn Alternation in Pill Bugs
(armadillidium vulgare)

Tohru Moriyama 153


Politics and People in Ethology: Personal Reflections
on the study of animal behaviour by Peter H. Klopfer

Nancy Innis 171

Comparative Psychology: A Handbook(1998)
G. Greenberg and M.M. Haraway (Eds.)

Gilbert Gottlieb 175

by the International Society for Comparative Psychology, an affiliate of the International
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COPYRIGHT 2000 by the International Society for Comparative Psychology. Published

ISSN 0889-3667 IJCPE8 12(3) 111-179 (1999)

International Journal of Comparative Psychology, Vol. 12, No. 3, 1999






Jim Scanlan
University of New England, AUSTRALIA

ABSTRACT: Analysis of speech-imitation sounds produced by pet budgerigars
{Melopsittacus imdulatus) reveals a consistent focus on acoustic components of speech
which have counterparts in the species-specific vocalizations of budgerigars. These
budgerigar vocalizations include whistle sequences (which, with their rapid glides in
pitch contour, need only slight modification to constitute a second-formant
representation of speech), the contact call (which is acoustically similar to the second-
formant transition of high front vowels), and sounds with harmonic spectra (which can
be modified to represent the formant structure of certain vowels). This transformation of
species-specific sounds into speech-imitation sounds by focusing on shared acoustic
features prompts the hypothesis that, with the appropriate social stimulation, pet
budgerigars perceive human speech as modified budgerigar sounds. The hypothesis is
supported by the fact that the shared acoustic features are particularly important cues in
the perception of species-specific communication sounds by both humans and
budgerigars. Such inter-species vocal communication cues, having a common origin
somewhere in vertebrate phylogeny. would help to explain the many reported examples
of human-like speech perception by nonhuman vertebrates. The shared neural
mechanisms which correspond to these shared acoustic patterns could constitute a
phylogenetically conservative level of auditory perception which is communication-
sound-specific but not species-specific.


Some birds, when kept as pets, copy the communication sounds
(i.e. speech) of their human companions. Although it has been valued as
an entertaining curiosity for thousands of years, this remarkable
behaviour has received relatively little scientific attention. Such
attention is warranted, however, because copies of speech sounds by
birds, when subjected to acoustic analysis, open new perspectives on

Address correspondence to Dr Jim Scanlan, c/- School of Biological Sciences,
University of New England, Armidale, NSW 2351, Australia.

© 2000 International Society for Comparative Psychology 1 1 1


avian vocal communication. Avian "speecii" (by which term I refer
both to speech-copying behaviour and to its acoustic manifestations)
represents human speech after it has been filtered through an avian
perceptual system, incorporated into an avian behaviour pattern, and
reproduced by means of an avian vocal mechanism. It can thus provide
a unique vantage point for the study of those perceptual, behavioural
and vocal mechanisms.

Also, by presenting us with sounds which we perceive as "speech"
but which differ, physically, from speech in a variety of ways, it can
provide insight into aspects of our own communication sounds which
are inaccessible to the self-scrutiny of conventional linguistics and
phonetics. Finally, in demonstrating that congruent vocal mechanisms
are not necessary for acoustic communication between two individuals,
it emphasises the predominance of auditory over articulatory factors in
vocal communication generally.

This paper will argue, on the basis of acoustic data and behavioural
observations, that speech-trained, pet budgerigars {Melopsittacus
undulatus) perceive speech sounds as modifications of species-specific
budgerigar sounds, and are able to copy those "modifications" in
communicative behaviour directed towards their human companions.
This behaviour is facilitated principally by three factors:
communicatively significant acoustic similarities between budgerigar
sounds and speech (explained below); the budgerigar's adoption of
those similar - albeit "modified" - communication sounds because of
social bonding with a human being; the budgerigar's ability to continue
modifying its communication sounds throughout life (Farabaugh et ai,
1994; Brittan-Powell et al, 1997) to match those of its social

The behavioural and acoustic evidence that birds perceive non-
species-specific communication sounds (e.g. those of human speech) as
if they were species-specific suggests that the former are being
processed by neural pathways normally dedicated to the perception of
the latter. This could be facilitated by acoustic patterns and
corresponding neural mechanisms which are common to the vocal
communication systems of birds and humans.

The published literature has established a rigidly dichotomous
perceptual model according to which, at any particular point along the
human auditory pathway, neural processing of speech is either
"acoustic" or "phonetic". Within the framework of this model, human-
like processing of some speech sounds by nonhuman animals is
adduced as evidence that aspects of speech perception previously
thought to be "phonetic" must, in fact, be "acoustic". This paper is
based on analyses of budgerigar "speech" which suggest that the birds


perceive certain acoustic features of speecii as being functionally
identical to acoustically similar features of budgerigar sounds. It
hypothesises an intermediate level of analysis which is communication-
sound-specific but not species-specific. Further testing of the
hypothesis could help us to escape between the horns of the dilemma
posed by the artificial "acoustic-phonetic" dichotomy. It could also lead
to new insights into the evolution of vocal communication - including
human speech.

The aims of the paper are thus to present some unprecedented
observations of budgerigar "speech", to propose an explanatory
hypothesis and to show how that hypothesis relates to current
knowledge and theory. In pursuing the last-mentioned aim, the
remaining Introduction selectively draws on the extensive literature
relating to avian vocal communication and the Discussion draws on the
even more extensive speech-perception literature. While neither section
is intended as an exhaustive review, some detailed discussion of this
literature was considered necessary.

Acoustic similarities

Bertram (1970) and Nottebohm (1976) drew attention to acoustic
similarities between human speech sounds and certain species-specific
vocalizations of the Indian hill mynah (Gracula religiosa) and the
orange-winged Amazon parrot (Amazona amazonica) respectively.
Each author associated these similarities with the ability of his subject
species to imitate speech sounds. In both cases, the speech-like species-
specific vocalizations are used in "close-range social contact" (Bertram,
1970), and their acoustic structure resembles that of human vowels in
their low-frequency periodicity and apparent formant structure.

Some calls and song syllables in the complex vocal repertoire of
the budgerigar display these and other speech-like features. The
budgerigar repertoire consists of at least 1 1 (and possibly as many as
14) call types (Higgins, 1999, p. 515) as well as the complex and
variable vocal pattern known as "warble" (Brockway, 1964, who
distinguished between "loud warble" and "soft warble") or "warble
song" (Farabaugh et ai, 1992). The latter term is used here, as it
emphasises the important fact that this vocal pattern is in some respects
analogous to passerine song. Indeed, Ferrell and Baptista (1982)
maintain that budgerigar warbling is "functionally equivalent" to
passerine song. Warble song consists of call notes as well as song-
specific syllables (Wyndham, 1980; Farabaugh et ai, 1992; Brittan-
Powell et al, 1997), providing psittacine support for the theory that bird
song evolved from calls (Thorpe, 1958; Thielcke, 1966; Catchpole,


Brockway (1964) described "loud warble" as "the chatter so
commonly associated with this species". The use of the word "chatter"
suggests the speech-like quality of budgerigar warble song, and the
spectrograms of Farabaugh et al. (1992) and Wyndham (1980) confirm
this similarity. Some warble song syllables are broad-bandwidth sounds
with formant-like concentrations of energy - particularly in the region
of human second-formant frequencies (about 800-2,500 Hz).

Behavioural parallels between warble song and speech imitation

Brockway (1964), Farabaugh et al. (1992) and Wyndham (1980) all
remark on the highly variable nature of warble song. In spite of its wide
range of syllable types and the high variability of its sequencing,
Farabaugh et al. (1992) detected the possible existence of combinatorial
rules and therefore of a learnt "syntax" in the structure of warble song.

Warble song is primarily a courtship vocalization (Brockway,
1964; Wyndham, 1980; Farabaugh et al, 1992), but can be used in
other forms of social interaction (Farabaugh et al., 1992) . Wyndham' s
(1980) observations, and the studies of Farabaugh et al. (1992, 1994),
indicate that warble song contains cues for individual (and group)
identification. Warble song is most commonly performed by males, but
can also be performed by females (Ferrell and Baptista, 1982). Its
performance is highly "mimetic" (Bockway, 1964; Ferrell and Baptista,
1982): one budgerigar is stimulated to warble by hearing another.
However, a warbling performance is not obviously directed at any other
individual (Brockway, 1969).

Vocal imitation plays an important role in warble song acquisition
and modification, with social factors influencing the pattern of imitative
learning. Farabaugh et al. (1992) found that males in the same social
group shared a significantly greater percentage of syllable types than
males in different social groups. The contact call, which is one of the
most common components of warble song, is both learnt from adults
and matched among siblings. Even if the adult model is aberrant (due to
deafening) or of another species (e.g. zebra finch, Taeniopygia guttata),
its influence is evident in the contact calls of juvenile budgerigars
(Brittan-Powell et al., 1997).

These characteristics of the budgerigar's warble song have their
parallels in the "verbal" (i.e., speech-imitation) behaviour of the birds.
Male budgerigars are recognised by fanciers as the best "talkers", but
females are capable of imitating speech. Verbal behaviour in this
species is usually stimulated by human chatter or noise in the
environment; thus it is "mimetic" in Brockway's sense, as well as being


imitative in its use of vocal copying. The budgerigars recorded during
the present study showed, when "talking", no interactive orientation
towards any human companion; their verbal utterances were seldom in
direct response to utterances of a human speaker.

In contrast to the verbal behaviour of budgerigars, that of some
other "talking" species, such as some larger parrots and the Indian hill
mynah, is often an overt interaction with human companions. Whereas
the budgerigar, once in the necessary psycho-physical state of arousal,
tends to run right through the verbal repertoire in a fixed order, these
other species are more inclined to produce particular verbal utterances
as a direct and specific response to verbal or other environmental
stimuli. I have argued [Scanlan, 1988] that this behavioural distinction
reflects the modelling of budgerigar "speech" on singing behaviour, in
contrast to the modelling of mynah "speech", or that of the larger
parrots, on calling behaviour.

The following three sections discuss the ontogeny and
neuroethology of learnt avian vocalizations with relation to budgerigar
"speech" and human speech. For a review of the literature relating to
ontogenetic and neuroethological correspondences between human
speech and oscine song, see Doupe and Kuhl (1999).

The development of avian "speech": ontogeny of song in birds parallels
that of speech in humans

The two Melopsittacus undulatus subjects of this study had been
carefully trained by their owners to repeat a fixed repertoire of phrases
and verses. Both these birds, before entering upon their repertoires,
would go through a preparatory performance which began as species-
specific warble song and included an ever-increasing number of speech-
like sounds until the repertoire itself was begun. This sequence, which I
have called "pre-performance warble" (Scanlan, 1988), contains speech
phrases and syllables which are not part of the performance repertoire.
This conforms with the eclectic nature of warble song as described by
Brockway (1964), Wyndham (1980), and Farabaugh et al. (1992). It
also suggests a possible connection with the plastic song of songbirds,
which includes a wide variety of vocalizations and, in some cases,
imitations of other species. (See Thorpe, 1955, and Marler, 1956,
although these early studies had not yet distinguished between "plastic
song" and the ontogenetically earlier "subsong".) Physically, oscine
plastic song as presented in the literature has a broader - and therefore
more speech-like - spectral envelope than full song. (See spectrograms
in, for example, Thorpe and Pilcher, 1958, and Marler and Peters,
1982.) Like warble song and speech imitation in budgerigars, it is


mainly performed by males, but can be performed by females.

The "pre-performance" or speech-like warble of pet budgerigars
has its parallels in the vocal behaviour of other "talking" species.
Groups of captive Indian hill mynahs (Foss, 1964) and European
starlings, Sturnus vulgaris (West et «/., 1983), exposed daily to the
speech of their human carers, developed vocal timbres and cadences
which resembled those of speech.

Many authors, including Charles Darwin in The Descent of Man
(1871), have compared subsong and plastic song in songbirds with
babbling in human infants. (See, e.g., Thorpe, 1961; Kuhl, 1989; Locke,
1993.) Menyuk and Menn (1979), in discussing the babbling of infants,
describe the boundary between babble and speech as "in general a fuzzy
one". At this stage in the child's development, they say, there are
"recurrent entities" in a child's production that cannot be classified
unequivocally as either "babble" or "speech". In some children these
entities "occupy a pivotal position in language development, and
careful consideration of their form and function illuminates the nature
of the transition from babble to speech in the general case" (Menyuk
and Menn, ibid.). This paper examines some analogous "entities" in the
pre-performance warble of "talking" budgerigars. These "entities" are,
in their acoustic structure, transitional between species-specific sounds
and speech-imitation sounds. In this, as well as in their loose overall
organization and their preparatory, exploratory function, they resemble
avian plastic song. Thus they provide clues to the motivation and the
mechanisms involved in the transformation of budgerigar sounds into
"speech". (The word "transformation" in this paper refers both to
modifications of acoustic structure, and to the - much more dramatic -
change in the corresponding aural impression.)

Social and sequential factors involved in avian vocal learning

At least some songbirds - e.g. zebra finches (Slater et ai, 1988) and
white-crowned sparrows, Zonotrichia leucophrys (Marler, 1970) -
appear to be genetically predisposed to learn species-specific song, but
cross-fostering experiments with both finches (Immelmann, 1969;
Eales, 1987, 1989) and white-crowned sparrows (Baptista and
Petrinovich, 1984, 1986) have demonstrated that any such
predisposition can be overridden by social factors. Furthermore, in
laboratory finches, social interaction - visual as well as vocal - between
tutor and pupil is necessary for song learning to occur with a precision
comparable to that observed in the wild (Eales, 1989).

Although, in captivity, some birds can learn species-specific song
from tape recordings (Marler and Tamura, 1964; Adret, 1993), the


learning of species-specific calls and songs by a bird typically involves
a familial (e.g. Clayton, 1987), social (e.g. Payne, 1981) or antagonistic
(e.g. Baptista and Petrinovich, 1984) relationship with the model/tutor.
In the earlier study on which this paper is based (Scanlan, 1988), it was
argued that learning of non-species-specific vocalizations by birds is of
two distinct kinds - that in which there is such a relationship with the
model, and that in which there is no such relationship. In the former
case, the overall behaviour pattern (including ontogeny,
neurophysiology, and social context) is exactly the same as that in the
learning of species-specific sounds and should thus be referred to by the
same term ("vocal imitation"). The term "vocal mimicry", then, should
be restricted to those instances of non-species-specific vocal copying in
which no familial/social/antagonistic relationship is involved (and in
which, as a corollary, ontogenetic and neurophysiological patterns
differ from those associated with "imitation"). The argument of this
paper involves classifying speech imitation by budgerigars as "vocal

Social factors determine the species-specific call-learning
behaviour of budgerigars. Farabaugh et al. (1994) found that the contact
calls of unrelated budgerigars converged on a common acoustic pattern
soon after they had been confined together in the same cage. (Nowicki,
1989, reported a similar result with the flock-recognition call of the
black-capped chickadee, Panis atricapillus.) Evidence presented below
will demonstrate that modification of the contact call is an important
ingredient in the process of a budgerigar's transforming species-specific
sounds into "speech".

Early experiments on song learning in captive birds (e.g. white-
crowned sparrows - Marler, 1970, and zebra finches - Immelmann,
1969) established the concept of a "sensitive period", after which
normal learning could not occur. However, further experimental work
with both these species (white-crowned sparrows - Baptista and
Petrinovich, 1984, 1986; zebra finches - Eales, 1985, 1987) made it
clear that the sensitive period was not immutable, but could be
extended if a suitable model had not been found by the end of the usual
song-learning period.

There is a growing body of evidence that, in the wild, vocal

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