Physical characteristics, categories and functions of
song in the Indian Robin Saxicoloides
fulicata (Aves: Muscicapidae)
Anil
Kumar
High
Altitude Regional Centre, Zoological Survey of India, Solan, Himachal Pradesh
173211, India
Email: anil_rathi@yahoo.com, anilsonta@gmail.com
Date of publication (online): 26 July 2011
Date of publication (print): 26 July 2011
ISSN 0974-7907 (online) | 0974-7893
(print)
Editor: Aziz Aslan
Manuscript
details:
Ms # o2630
Received 19
November 2010
Final
received 31 May 2011
Finally
accepted 30 June 2011
Citation: Kumar, A.
(2011). Physical characteristics, categories and functions of
song in the Indian Robin Saxicoloides
fulicata (Aves: Muscicapidae). Journal
of Threatened Taxa 3(7): 1909–1918
Copyright: © Anil Kumar
2011. Creative Commons Attribution 3.0 Unported License.JoTT allows unrestricted use of this article in any medium for non-profit
purposes, reproduction and distribution by providing adequate credit to the
authors and the source of publication.
Author Details: Dr. Anil Kumar is a scientist in ZSI,
Solan. Over the years his research work is focused on communication of birds.
So for, he has recorded over 200 avian species mainly from Himalaya and
contributed over 30 research papers/ articles. For ZSI, he has worked on some
departmental research projects pertaining to mainly faunal studies.
Acknowledgements: I am grateful
to Director, ZSI, Kolkata for his kind encouragement
and support. I am grateful to
Director, Wildlife Institute of India, Dehradun, for encouraging and extending
me institutional facilities during the course of study. I am thankful to Dr.
Ajeet Singh (Haridwar), Dr. Romesh Kumar Sharma (Haridwar), Dr. Himmat Singh
(Jodhpur), and Dr. Rajah Jayapal (WII) for their cooperation at various levels
during the study. Financial support from DST under SERC Fast Track scheme
(Project no. SR/FTP/LS-166/2000) is also gratefully acknowledged. Special
thanks are due to Shri Anand Arya (Noida) for providing a nice image of Indian
Robin.
Justification
for delayed publication:
During
2005, I was selected as a scientist in the ZSI and posted at Itanagar,
Arunachal Pradesh for about five years. The lack of bio-acoustic facilities and
relevant literature in the early phase of my posting, and prolonged illness of
two family members led to the delay in publication -- Anil Kumar (author).
The song
characteristics and functions of the species do not change in ten years. There
are no new studies on this topic and therfore the findings are informative and
provide a base line for the song features of the species -- Aziz Aslan (subject
editor).
Abstract: The
physical characteristics and biological significance of song in the endemic
Indian Robin Saxicoloides fulicata are
described. Songs are discrete and
composed of strophes (structural units) with frequency ranging from 1.03 to
8.00 kHz, preceded and followed by temporal intervals from 0.21 to 21.25 sec.
Occasional, monosyllabic whistles are also identified. In a song bout usually
the same type of strophe is repeated several times in a stereotyped manner with
minor structural variations of elements before switching to another type of
strophe. Most strophes are composed of two to five elements, having both simple
and complex structure. Two categories of songs have been identified on the
basis of their acoustical features and context of production. Type-A songs are
simple, stereotyped, spontaneous and common, while type-B songs are rare,
female-oriented and more complex than type-A. Song is used in both inter- and
intra-sexual contexts. It seems that type-A songs are driven by male-male
competition for territory and mates. Males also shorten the length of strophes
and reduce gaps between strophes (in type-B songs) on the arrival of females in
the vicinity, most probably to increase the song rate, suggesting it to be an
indicator of male quality.
Key words: Indian
Robin, Saxicoloides fulicata, song organisation, song characteristics, song function.
For figures,
images, tables -- click here
INTRODUCTION
Mate acquisition and
male-male competition are responsible for the evolution of song in passerine
birds (Catchpole & Slater 1995). Song characteristics such as acoustical features, mode of production,
temporal patterns and structural complexity (variability of elements) are
highly diverse among oscine birds (Marler & Slabbekoorn 2004). Many passerine species sing two
categories of songs that differ in their patterns of temporal, spatial and
contextual use (Spector 1992). The
first category songs are often simple and highly stereotyped, sung at
relatively low rates. In contrast,
second category songs are usually more complex and variable, and sung at higher
rates (Highsmith 1989; Kroodsma et al. 1989; Staicer 1989; Bolsinger
2000). Studies on the functions of
song (with some exceptions) suggest that type-A songs (more stereotyped) are
used as intersexual signals, while type-B (more variable) are used
intrasexually (Kroodsma 1981; Spector 1992; Bay 1999). Mode of singing also varies in birds.
Mostly oscine birds use two types of singing mode i.e., ‘repeat’ or ‘eventual
variety’ (singer produces one song type/strophe repeatedly before switching to
another type of strophe), and ‘serial’ or ‘immediate variety’ mode (singer
produces a variety of song strophes/ phrases without any apparent rule) (Molles
& Vehrencamp 1999).
In many species song
repertoire is organised around a limited number of strophes or song types, such
as in the White-crowned Sparrow Zonotrichia
leucophrys, where each male uses only a single,
simple, monotonous song in stereotyped manner (Baptista 1975). Some other species, namely European
Redwing Turdus iliacus(Bjerke & Bjerke 1981), Splendid Sunbird Necterina coccinigastra (Grimes 1974) and
Ovenbird Seiurus aurocapillus(Falls 1978) are also known for their small repertoire size. While in others, such as in Mokingbird Mimus polyglottos (Howard 1974) and Sedge
Warbler Acrocephalus schoenobaenus(Kroodsma & Parker 1977; Catchpole 1976), the songs composed of a large
number of dissimilar structured song elements with an unrestricted number of
combinations (Catchpole & Slater 1995).
Robins belong to old
world Chats-Flycatchers (Muscicapidae) with some exceptions; the American RobinTurdus migratoriusand Mountain Robin T. plebejusbelong to family Turdidae, the Scarlet Robin Petroica multicolor belongs to the family
Petroicidae (del Hoyo et al. 2006). Robins use both simple and complex vocalisations for communication
(Bhatt et al. 2000; Kumar & Bhatt 2001). For example, European Robin Erithacus rubecula use a complex,
melodious song (made up of prolonged notes, short warbles and trills) for
territory defence, almost throughout the year (Hoelzel 1986, 1989; Scriba &
Goymann 2010). African Forest
Robins (Stiphrornis)
have been reported to use two types of vocalisations (Beresford & Cracraft
1999). However, functions of these
categories remain unclear. Similar
patterns of vocalisations were also reported in a recently discovered species
of African Robin, the Olive-backed Forest Robin Stiphrornis pyrrholaemus (Schmidt et al.
2008). Oriental Magpie Robin Copsychus saularis also use two distinct
categories of songs, which differ in structure and functions (Bhatt et al.
2000; Kumar 2003).
The Indian Robin Saxicoloides fulicata (Muscicapidae) is an
endemic, small-sized (19cm), passerine species, distributed throughout the
Indian subcontinent except northeastern, higher Himalaya and Thar Desert, and
is divided into a few races. It is
a common, resident, territorial and sexually dimorphic bird. Males have glossy black under parts and
a white shoulder patch (Image 1), while females have grayish-brown upperparts
and grayish under parts and lack white shoulder patch. It prefers dry, stony areas with sparse
scrub, arid stony ridges, low rocky hills outcrops, edges of cultivation and
deserted buildings, gardens and groves (Ali & Ripley 1983; Grimmett et al.
1998). Information is scanty on
the singing behaviour & sociobiology of the species (Nirmala & Vijayan
2003). In this article, I describe
and quantify the organisation of song in terms of physical characteristics,
categories and context of production in the Indian Robin for the first time.
METHODS
Field recordings
Songs of 23 male Indian
Robin were recorded in their natural habitat from four different places in
northern India. Recordings on 11
individuals were made in Dehradun (30026’N & 78006’E)
during May 2002 to February 2005; during the same period, five birds were
recorded at Srinagar, Garhwal (30021’N & 78077’E);
two at Haridwar (29055’N & 78008’E); and five
recordings in and around Jodhpur (26021’N &73006’E)
during March–April 2001. All
birds recorded were unbanded. To avoid recording the same individual twice,
each bird was recorded only when it was within view and recordings were made in
each area only once. A total of
183 recordings (2–9 per individual) were made ranging 2–14 minutes
duration. Signals were recorded
using Sony CFS 1030S or Sony PCM-M1 or Marantz PMD 222 sound recorders and JVC
MZ-500 or Sennheiser ME-66 microphones. Behavioural correlates were used to infer the possible meaning of the
song.
Data analysis
Recordings were
digitised using M-Audiophile 2496 (sound card) at the sampling rate 48kHz and 16 bit resolution. After editing, cuts of high quality recordings (excluding recordings of
five individuals due to poor quality) were analyzed with the help of windows
based sound analysis software, Avisoft SAS Lab Pro (version 4.1). Spectrograms were displayed on a
computer monitor and measurements of variables were made using frequency and
time courser. Dominant frequency
of given strophe was analysed generating power spectrum. The frequency of highest peak was
recorded. For the sequential
analysis of strophes, spectrograms were printed using several line mode. In this
mode, about 40sec long recording was printed in seven lines on A4 size paper in
landscape page setup. All
spectrograms were calculated using following setting of SAS Lab: 512
FFT-length, 75% Frame, Hanning window and 87.5% time window overlap. In the present study, minimum and
maximum frequency, frequency bandwidth, dominant frequency (frequency of
maximal amplitude), duration and intervals in song strophes were measured. Number and types of elements per
strophe, song rate (strophes per minute) and complexity level (types of
elements per min.) were calculated to define the acoustical features of songs. Results were expressed as mean±SE. Non-parametric statistics was used to
measure the level of significance in differences, since most data were not
normally distributed. Windows
based software SPSS was used for the analysis.
Song terminology
Study of literature
reveals that there is no standardization of terminology for the songs of
different species. Indeed,
different authors used different terms for the same songs features (Spector
1992). I labeled structural units
of song on the basis of morphological features, using terminology partly
adopted from literature (Staicer 1989; Bay 1999). The song in Indian Robin consists of a number of distinct
sections, called strophes or phrases and each strophe consists of several
smaller units known as elements (Fig. 1). An element is a short tracing on the spectrogram. On the basis of frequency modulations
the elements can further be classified into simple (constant pitch,
un-modulated or slightly modulated frequency) and complex (varied pitch,
rapidly modulated or multi harmonic frequency) elements. In a song bout, in
different phrases, often bird use a combination of one to three elements
together and is named as a syllable (Catchpole & Slater 1995).
RESULTS
Physical characteristics
Males sang during the
breeding season mostly in the morning (0500–0900 hrs) and evening (1700–1730
hrs). Individuals were observed
singing from exposed branches of trees, rocks, walls, electricwires and on the ground. The song
of Indian Robin was composed of strophes with occasional whistles (Fig.
2). The strophes were made up of
one to nine elements, with dissimilar structure and occasional repetition of
elements. The frequency of song
ranged from 1.03 to 8.00 kHz. Dominant frequency of most songs was 4.2 kHz (2.3–6.5 kHz). Average duration of strophes was 0.68±0.03
to 0.21±0.02 sec. preceded and followed by temporal intervals ranging 6.34±0.46
to 0.61±0.03 sec. Songs were
produced at variable rate; 9.33±0.67 strophes per
minute in song type-A and 70.56±3.71 strophes per minute in song type-B (Table
1).
Indian Robin sang in
moderate sized song bouts ranging one to six minutes duration (sometimes <1
or >6 min). Different types of
temporal patterns were identified. On the basis of sequence of strophes, three categories were
observed. However, distinction is
purely temporary and individuals do not follow strict rule in sequencing. Two to nine types of phrases with
modulated frequency were identified in song bouts. However in most cases (74%) males used two to three types of
phrases. Occasional whistles were
also observed. These were monosyllabic in structure and uttered 1–5 times
between any two consequent phrases of a song bout.
Stereotyped mode
In many cases (58%), the
bird repeated a particular strophe in stereotyped order with minor structural
variations of elements (Fig. 2A, element g in P1 is replaced by f in P2 and
elements c, d & e showed variations in their minimum and maximum
frequencies, respectively, and adding or deleting of an element, such as in
Fig. 2B, element f of P1 is omitted in P3). This mode was observed mainly in isolated birds (N=9) with
no conspecific neighbor.
Alternative mode
In this mode individuals
produced two or three types of phrases in alternative manner (Fig. 2C). For instance, bird D1 (Table 2)
produced a and b phrases alternatively and bird J1
produced a, b, c and d phrases alternatively without fixed number and sequence
and new phrases such as e and f, in a recording. In some recordings occasional whistles were also used
between phrases (Fig. 2D). This
mode of singing was observed only in birds (N=3) having conspecific neighbours.
Complex mode
Contrary to type-A songs
in stereotyped mode (Fig. 3A), in some cases (16 %) such as type-B songs, birds
produced large number of phrases randomly with out any strict order in sequence
(Fig. 3B, C). However, repetition
of phrases (such as in Fig. 3B and C, Type 1 repeated as P1, P5 and P7) and
re-assortment of elements/ phrases (such as Type 2 as P2, P8 and P12 in Fig. 3B
and C) were identified, for example type-B (Table 2) songs of bird D1.
Song categories and functions
Syntactically two
categories of songs were identified (Fig. 3). Type-A songs were common (84% of
total songs recorded) in breeding season and consisted repeated strophes having
0.68±0.03 sec duration and followed by 6.34±0.46 sec gap.
Usually, the bird repeated a particular strophe several times before switching
to another strophe. These songs
usually uttered during territory advertisement and to maintain pair-bond. However, territorial conflicts were not obvious (n=5). This could be the result of low
population densities of this species in northern India (pers. obs.; unpub.
data). Mostly solitary pairs were
observed in a particular area.
Type-B songs were more
complex (Mann-Whitney U-test; U=8.5, p<0.001) and rare (only 16% of songs
recorded) as compared to type-A songs. Most acoustical characteristics significantly differ (Table 1) from
type-A songs except dominant frequency (P=0.844). Type-B songs were consisted of short strophes having 1–4
elements. The duration and gap of
strophes were significantly lower (p<0.001) then type-A songs. The males produced 70.56±3.71 strophes
per minute. These songs were observed only in the presence of females and
during courtship. Courtship
displays were also associated with these songs. During these displays male birds were observed running on
the ground or on a wall 0.65 to 2.15 m towards a female with splayed and
erected tail, forwarded beak and lowered head while emitting a complex
song. Within a few seconds the
male mounted the female for insemination.
DISCUSSION
Physical characteristics
In the present study,
the Indian Robin used stereotyped songs, organised around a limited number of
strophes (except type-B songs). Studies on temperate song
birds provide some insights on how song output is organised. Like the Indian Robin, Chaffinch Fringilla coelebs use three or four song
types (phrases) in its song, with a sequence of each in turn before returning
to the first (Slater 1983). Sequence of song types is not always the same and
the phrases are not necessarily sung with equal frequency. It is quite common in many species for
one song to comprise a much larger part of the bird’s output than another
(Catchpole & Slater 1995). Degree of song variability is highly diverse in birds and song
characteristics may also vary temporally and spatially (Catchpole & Slater
1995). Tawny Pipit Anthus campestris use short and simple
songs (Osiejuk et al. 2007) and males are known to have single song type
repertoire (Neuschultz 1986). In contrast, Chaffinch Fringilla coelebs, Great Tit Parus major, Ring Ousel Turdus torquatus and Dark-eyed Junco Junco hyemalis use several song types
(Krebs et al. 1978; Slater 1981; Ince & Slater 1985; Williams &
MacRoberts 1977), while others, like Red-eyed Vireo Vireo olivaceus and Marsh Wren Cistothorus palustris use 12 to >100 song
types in their repertoire (Borror 1981; Kroodsma & Verner 1987). Common Nightingale Luscinia megarhynchos have a large repertoire
(up to 260 different song types) divided into whistle songs and nonwhistle
songs (Kipper et al. 2004; Kunc et al. 2005).
In most oscine birds,
song complexity serves as an honest signal of male quality (Hesler et al.
2011), and selection may also favour song parameters such as song rate and song
length (Garamszegi & Møller 2004; Kunc et al. 2005). In species with large
repertoire, sexual selection might favour the evolution of structural song
traits such as whistle songs in nightingales (Kunc et al. 2005), thought to be
evolved to attract migrating females at night (as structurally simple whistles
suffer less from spectral degradation during propagation over long distance;
Slabbekoorn et al. 2002). While, in species with a small repertoire, it may favour song
length and song rate, as reported in some species such as Willow Tit Parus montanus(Welling et al. 1997) and Hoopoe Upupa
epops (Martiu-Vivaldi et al. 2002). In the present study, Indian Robin used song in both inter-
and intra-sexual contexts. When inferred with the behavioral observations,
type-A songs were driven by male-male competition for territory and mate acquisition. Males also shortened the length of
strophes and reduced gap between strophes (in type-B songs) on the arrival of
females in close vicinity, most probably to increase song rate, which could
also be an indicator of male quality as suggested for other species.
The songs of Indian
Robin range from 2.19 to 6.96 kHz frequencies. The dominant frequency (i.e. 4.2 kHz) of songs was considerably higher
then expected for its body weight. Wallschlager’s regression function
(Wallschlager 1980) of ‘central frequency’ on body weight predicts a frequency
of 3.6 kHz for birds having body weight (i.e. 18–19 g) like Indian Robin
(Ali & Ripley 1983). Similar
trends have also been reported in some South American passerines (Ryan &
Brenowitz 1985). Lambrechts (1996)
suggested that birds should have greater performance at about one-fourth of
their frequency range.
Indian Robin produced
its song in three different modes. In stereotyped mode, in a song bout bird
produced same phrase again and again (like …AAAAA….), while, in alternative
mode bird used two or three types of phrases (like ….AAA…BBBB…AAAA….BB….CCCC…). Third mode of production was complex and
observed only in type-B songs. In
the literature, singing mode refers to the sequential pattern of song type
(strophes/ phrases) production (Molles & Vehrencamp 1999). It is classified as ‘repeat/ eventual
variety’ such as ‘stereotyped/ alternative mode’ of singing in Indian Robin,
and ‘serial/ immediate variety’ analogue to ‘complex mode’ of singing in
present study. Previous studies
showed that in some species singers increase their switching rate among song
types during agonistic conflicts and on the arrival of female (Kramer et al.
1985; Langmore 1997). In the
present study it seems that Indian Robin used the stereotyped mode of singing
in low territorial pressure situations (where conspecific territorial neighbors
were absent) and the alternative mode in relatively high territorial pressure
situations (when the singing male had a conspecific neighbour). Although not substantiated conclusively
in the present study, it opens scope to test this hypothesis in future studies.
In the present study, it
was observed that the Indian Robin mostly sing in morning and evening hours,
like many other passerines (Catchpole & Slater 1995). Catchpole (1973)
studied the diurnal rhythms of song production in two European Acrocephalus species, the Reed (A. scirpaceus) and Sedge (A. schoenobaenus) warblers. He observed a marked peak of singing
activity around dawn and dusk in these species. The acoustic transmission hypothesis (ATH) predicts that
birds sing their full songs most intensively at dawn because this is the time
of the day when these songs propagate most effectively and hence should be most
effective for long-range communication (Henwood & Fabrik 1979). However, experiments made by Dabelsteen
& Mathevan (2002) on Blackcap Sylvia
atricapilla in temperate deciduous forests, indicate
that the dawn singing can’t be understood only by ATH, some other factors such
as feeding and social conditions may also be responsible for dawn singing. I am
unable to contribute to these ideas but the Indian Robin can be a suitable
model to test the ATH in tropical habitats in future studies.
Song categories and functions
On the basis of
acoustical features and context of production, two categories of songs were
emerged in Indian Robin. Type-A songs were simple, stereotyped, spontaneous and
common, while type-B songs were rare, female oriented and more complex
(Mann-Whitney U-test; U=8.5, p<0.001) than type-A. In such a manner, two or more acoustically distinct song
classes have been reported for some passerine birds (namely Dark-eyed Juncos,
Titus 1998; Field Sparrow Spizella pusilla,Nelson & Croner 1991; Yellow-throated Vireo Vireo flavifrons, Smith et al. 1978;
Yellow-rumped Caciques Cacicus cela,Trainer 1987; Red-vented Bulbul Pycnonotus cafer,Kumar 2004; Oriental Magpie Robin, Kumar 2003). In some species, such as European Blackbird Turdus merula (Dabelsteen & Pedersen 1990),
European Robin (Dabelsteen et al. 1997), Lesser Whitethroat Sylvia communis (Balsby 2000) and Song
Sparrow Melospiza melodia(Anderson et al. 2008), songs are described as ‘broadcast songs’ (type-A songs
of Indian Robin) and ‘soft songs’ (type-B songs of Indian Robin) also termed as
‘quiet song’, ‘twitter song’ or ‘whisper song’ in previous studies (Anderson et
al. 2008). Like the Indian Robin,
the first category songs of these species were loud and conspicuous and second
category songs were soft, low amplitude and rare, used in different contexts
such as female courtship, male-male aggression or both (Dabelsteen et al. 1998;
Titus 1998; Anderson et al. 2008). However, in Indian Robin, type-B songs were used only for mating/ courtship
purpose but the scope of present study limits us from discounting this feature
for other functions in other seasons. Some species of North American wood-warblers(Parulidae) also sing two categories of songs. The first category songs of these species were often simple
and highly stereotyped, sung at relatively low rates and near females. While, second category songs were
usually more complex and variable, sung at higher rates and in male-male
interactions (Spector 1992; Bolsinger 2000). In contrast with wood-warblers song system, in the present
study, Indian Robin used simple and stereotyped songs for territory/pair-bond
maintenance and, complex and varied songs for mating.
Some hypotheses have
been proposed to explain the proliferation of song categories in birds (Nelson
& Croner 1991). It is hypothesized
that all song types (phrases) within the vocal repertoire of a species may have
the same purpose. Evolution of
large numbers of song types in a species may be favored by both inter- and
intra-sexual selection. Large
repertoires may effectively repel the rival males by appearing to represent the
presence of several singing males. Large repertoires might also be favored by femalesduring mate selection (Catchpole 1980). Another hypothesis assumes that different song categories/ song types
within a repertoire contain different information (Smith et al. 1978; Trainer
1987). Different song types are
sung in different behavioural contexts, and thus appear to provide different
information to listeners. In the
present study, the Indian Robin used two categories of songs in different
behavioural contexts; it seems that second classhypothesis may fit to understand the evolution of song in this species.
CONCLUSION
Studies carried out
during the last five decades on the quantification of complexity and
variability in bird song provides deep insights in understanding the evolution
of song and sexual selection in temperate birds. It is now well-understood that the
complexity of songs in passerines play an important conceptual, theoretical and
empirical role. Studies on the
singing behaviour of Indian birds are restricted to comparatively few
species. It is believed that most
tropical birds exhibit quite different social systems than temperate
species. Communication
systems of most Indian birds cannot be properly understood based only on the
information available from temperate birds. So, extensive long-term investigations are needed for the
characterisation and documentation of the vocal repertoire of Indian birds to
understand the evolution of song in these species. The present study is a base-line effort in this direction
and may possibly enable more detailed studies to be carried out in the future,
especially on repertoire size, individual variations, regional dialects, and
ecological and behavioural constrains on the evolution of song in Indian
birds.
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