RESEARCH ARTICLE
An Acoustic Analysis of the Genus Microhyla
(Anura: Microhylidae) of Sri Lanka
Nayana Wijayathilaka, Madhava Meegaskumbura*
Department of Molecular Biology and Biotechnology, Faculty of Science and Postgraduate Institute of
Science, University of Peradeniya, Peradeniya, KY, 20400, Sri Lanka
* madhavam@pdn.ac.lk
Abstract
a11111
OPEN ACCESS
Citation: Wijayathilaka N, Meegaskumbura M (2016)
An Acoustic Analysis of the Genus Microhyla (Anura:
Microhylidae) of Sri Lanka. PLoS ONE 11(7):
e0159003. doi:10.1371/journal.pone.0159003
Editor: Gianni Pavan, University of Pavia, ITALY
Received: February 5, 2016
Accepted: June 25, 2016
Published: July 12, 2016
Copyright: © 2016 Wijayathilaka, Meegaskumbura.
This is an open access article distributed under the
terms of the Creative Commons Attribution License,
which permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Vocalizing behavior of frogs and toads, once quantified, is useful for systematics, rapid species identification, behavioral experimentation and conservation monitoring. But yet, for
many lineages vocalizations remain unknown or poorly quantified, especially in diversity
rich tropical regions. Here we provide a quantitative acoustical analysis for all four Sri Lankan congeners of the genus Microhyla. Three of these species are endemic to the island,
but Microhyla ornata is regionally widespread. Two of these endemics, M. karunaratnei
(Critically Endangered) and M. zeylanica (Endangered), are highly threatened montane isolates; the other, M. mihintalei, is relatively common across the dry lowlands. We recorded
and analyzed 100 advertisement calls from five calling males for each species, except for
M. zeylanica, which only had 53 calls from three males suitable for analyses. All four species
call in choruses and their vocal repertoires are simple compared to most frogs. Their calls
contain multiple pulses and no frequency modulation. We quantified eight call characters.
Call duration and number of pulses were higher for the two montane isolates (inhabiting
cooler habitats at higher altitudes) compared to their lowland congeners. Microhyla zeylanica has the longest call duration (of 1.8 ± 0.12 s) and the highest number of pulses (of 61–
92 pulses). The smallest of the species, Microhyla karunaratnei (16.2–18.3 mm), has the
highest mean dominant frequency (3.3 ± 0.14 kHz) and pulse rate (77 ± 5.8 pulses per second). The calls separate well in the Principal Component space: PC1 axis is mostly
explained by the number of pulses per call and call duration; PC2 is mostly explained by the
pulse rate. A canonical means plot of a Discriminant Function analysis shows non-overlapping 95% confidence ellipses. This suggests that some call parameters can be used to distinguish these species effectively. We provide detailed descriptions for eight call properties
and compare these with congeners for which data is available. This work provides a foundation for comparative bioacoustic analyses and species monitoring while facilitating the systematics of Microhyla across its range.
Funding: This research was supported by the
National Research Council of Sri Lanka (NRC 11124) to MM, and the University of Peradeniya
Research Grant (RG/2012/45/S) to MM.
Competing Interests: The authors have declared
that no competing interests exist.
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Bioacoustics of Sri Lankan Microhyla
Introduction
Among amphibians, anurans (frogs and toads) are conspicuous for their calling (vocalizing)
behavior [1–4]. Acoustically well-studied vocal repertoires of anurans provide vital information on many fronts: ascertaining species identities, especially when cryptic species are involved
[5–11]; acoustic experimenting and understanding specific acoustic signaling in different
behavioral contexts [12–15]; bioacoustic monitoring, surveys, remote sensing and population
studies [16–18]. However, for this, the vocal repertoires of frogs need to be understood statistically. Such bioacoustic analyses for tropical regions of the world, where most of the anuran
diversity exists, are almost non-existent [19,20].
This is also true for the genus Microhyla, widespread throughout the tropics across India,
Sri Lanka, Indonesia, archipelagos of Ryukyu of Japan and Sulu of Philippines [21]. So far, 39
species of the genus have been identified [10,21], of which four (ca. 10%) are found in Sri
Lanka. The island is now a well-recognized hotspot of amphibian diversity and endemicity
[9,22,23], containing a unique assemblage of fauna and flora, distinct from Indian mainland,
with only a few shared species between the two regions. The genus Microhyla also shows the
same pattern of distribution, with three species being endemic to the island, and one shared
species [10].
Due to their widespread nature, only 4 of the 39 species are listed as threatened by the
IUCN, 2015 [24]; however, of these, two species, M. karunaratnei (Critically Endangered) and
M. zeylanica (Endangered), are confined to two mountain peaks of the Central Hills and Rakwana Hills of Sri Lanka. Furthermore, M. karunaratnei is considered an EDGE (Evolutionary
Distinct and Globally Endangered) species [25], the only species amongst Microhyla and the
only Sri Lankan amphibian to be included in this category. Though these species are prioritized
for conservation, their ecology, behavior and natural history is virtually unknown. A deeper
understanding of these threatened species will enable their effective conservation.
The vocalizations of only a few species of Microhyla have been analyzed or published up to
now. These include, M. bornensis (Borneo), M. berdmorei (Thailand), M. butleri (Thailand),
M. fissipes (Thailand), M. heymonsi (Thailand, India), M. laterite (India), M. petrigina (Borneo), M. ornata (India) and M. rubra (India), M. sholigari (India) [26–33]. So far call characterization work has not focused on the Sri Lankan members of this genus except for a population
of M. ornata from India [30] and M. mihintalei, a recently described species [10].
Here, we provide a quantitative description of the vocalizations for the three Sri Lankan
endemic species, M. karunaratnei, M. zeylanica, M. mihintalei, and a Sri Lankan population of
M. ornata. We provide descriptions of eight call properties measured for 353 calls from 18 individuals, which also help us evaluate the intraspecific variation within these species. We discuss
and compare the vocalizations of these species and point out the knowledge gaps, thus providing the basis for species monitoring and systematics of Microhyla across its range.
Materials and Methods
Ethics Statement
Research was conducted under the permission of Department of Wildlife Conservation (permit
no. WL/3/2/13/13) and Forest Department (permit no. R&E/RES/NFSRC/14) of Sri Lanka.
Specific methods of collection, euthanasia, tissue sampling and fixation followed the guidelines
for use of live amphibians and reptiles in field research by the American Society of Ichthyologists and Herpetologists (ASIH) (http://www.asih.org/pubs/herpcoll.html; dated 13 March
2006), and were approved by the ethical committee of Postgraduate Institute of Science, University of Peradeniya at its 16th meeting held on 14th November 2014.
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Bioacoustics of Sri Lankan Microhyla
Fieldwork and acoustic recordings
Calling males of Microhyla karunaratnei were recorded between 20:00–23:00 hours on 9th
December 2014 from a population in Morningside forest reserve, Suriyakanda, Rathnapura
district (6.4075°N, 80.6094°E, 1050 m.a.s.l). They were calling around a breeding pool, an abandoned gem-pit in a regenerating forest patch with tall grasses and shrubs. Fairly common, calls
of M. mihintalei and M. ornata were recorded from temporary breeding pools in Mihintale,
Anuradhapura district (8.3548°N, 80.5054°E, 120 m.a.s.l) on 27th September 2014 and Maakandura, Kurunegala district (7.3245°N, 79.9887°E, 30 m.a.s.l) on 25th August 2014 respectively. Calls of M. zeylanica were recorded from a shallow ephemeral pool in a grassland
habitat at Horton Plains National Park (6.7963°N, 80.8179°E, 2135 m.a.s.l) on 22nd and 23rd
August, 2014 between 21:00–02:00 hours (Fig 1). Samples of call recordings used in the analyses with collection numbers of each species are provided as supporting information (S1–S4
Audio), which will help direct and wider comparison with other taxa [34].
Calls of five males from each species (except M. zeylanica, N = 3) were recorded using a digital recorder, Marantz PMD 620 MKII (sampling rate 44.1 kHz, 16-bit resolution) and a directional Sennheiser-ME66 microphone equipped with a foam windscreen. Microphone was
handheld to maintain a distance of 0.3 to 0.5 m between calling male’s snout and the microphone tip. Gain setting of the recorder was adjusted prior to each recording and maintained
until the end of the given recording. Ambient temperature of the calling site was taken immediately after each recording using a handheld Kintrex IRT0421 non-contact infrared thermometer to the nearest 0.1°C. Snout vent length (SVL) and body weight (BW) of all recorded males
were measured in situ using a precision digital caliper and a portable digital balance to the
nearest 0.01 mm and 0.01 g respectively; one specimen from each species were taken as a reference sample and all other animals were released back to their original habitat upon taking measurements. Collected male was placed in a moist plastic container (200 ml) with some grass
blades or leaf litter and transported to the field station in less than 3 hours. It was then
Fig 1. Four Microhyla species in life and their distribution. (A) A map showing the distribution of Microhyla karunaratnei (blue), M. zeylanica
(green), M. mihintalei (red) and M. ornata (yellow). (B) Dorsolateral view of the four species (in life).
doi:10.1371/journal.pone.0159003.g001
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euthanized using Tricaine Methanesulfonate (MS-222), fixed in 4% formalin and preserved in
70% ethanol (M. karunaratnei DZ1530, M. zeylanica DZ1420, M. mihintalei DZ1445, M.
ornata DZ1427). The species identification was done using morphology [10, 35–38]. Tissue
samples (thigh muscles or liver) were taken immediately after euthanization and stored in
absolute ethanol at -20°C for further analyses at the Department of Molecular Biology and Biotechnology, University of Peradeniya (reference numbers: DZ1530, DZ1420, DZ1445,
DZ1427). Video recordings of vocalizing males were collected for all four species using a
Canon EOS 60D digital SLR Camera and a Sony DCR-SR45 camcorder using the night vision
mode.
Acoustical analyses
Only calls having a high signal to noise ratios that were free from overlapping calls of nearby
males were used for the analysis. A total of 100 calls were measured from each species (20 calls
per individual) except for one species, M. zeylanica, for which only 53 calls from three individuals were used due to the paucity of non-overlapping calls. Calls emitted by all species contained multiple pulses. Two species, M. karunaratnei and M. zeylanica, vary their call by
dropping pulses (discontinuing the pulse train while maintaining longer duration between
pulses several times within a call); however, this was observed only in five and four calls of the
two species respectively. We excluded such calls from the analysis.
We measured eight call properties for this study (Table 1). These included temporal properties
(call duration, call rise time, call fall time, 50% call rise time, 50% call fall time, number of pulses
per call and pulse rate) and a spectral property (call dominant frequency by averaging spectrum
over an entire call). Call characters were measured using methods and terminology from previous
studies [1,19,20] as illustrated in S1 Fig. Raven Pro 1.4. was used to measure the call characters;
temporal call characters were measured using Raven’s waveform display and spectral properties
were measured by averaging the spectrum over the entire duration of a call (256 pt. fast fourier
standard
transform, Hanning window). Descriptive statistics of the call characters; mean (X),
deviation (SD), range and percent coefficient of variation (CV ¼ SD=X 100; calculated as
within species CV, where SD is divided by the mean value of a species) were computed using
Microsoft Excel 2010. Median and interquartile range were calculated for indivisible characters
(number of pulses per call). Systat version 11 (SYSTAT 11) was used to conduct a principal component analysis (PCA) on the correlations matrix, using four call property variables. Call variables with high CV values (i.e. having CVs above 35%); Call rise time, Call fall time, 50% call rise
time, 50% call fall time were excluded from the PCA analysis. We also did a discriminant
Table 1. Descriptions of acoustic properties measured.
Properties of calls
Call duration (ms)
Time between onset of first pulse and offset of last pulse in a call
Call rise time (ms)
Time between onset of first pulse and pulse of maximum amplitude
Call fall time (ms)
Time between pulse of maximum amplitude and offset of last pulse
50% Call rise time (ms) Time between call onset and the half-amplitude point of earliest maximum peak in
the call waveform
50% Call fall time (ms)
Time between the half-amplitude point of the last maximum peak in the call
waveform and pulse offset
Pulses per call
Count of pulses (k)
Pulse rate (pulses/s)
(k– 1)/t, where t is the time between onset of first pulse and onset of last pulse
Dominant frequency
(kHz)
Maximum frequency using Raven’s selection spectrum function over the duration
of the entire call
doi:10.1371/journal.pone.0159003.t001
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Bioacoustics of Sri Lankan Microhyla
function analysis (DFA) using six call variables (two highly correlated call variables to call duration, call rise time and 50% call rise time, were removed from the DFA analysis) and produced a
canonical means plot using the first two canonical variables to verify the results of the PCA. For
all four species, we assessed the relationship of the call variables with temperature, SVL and body
weight using Pearson product moment correlation analyses (correlation coefficient = ρ).
Results
Among the four species, M. mihintalei is the largest (mean SVL = 24.6 ± 2 mm, N = 5), and M.
karunaratnei the smallest (SVL = 16.7 ± 0.9 mm, N = 5) with M. ornata (mean SVL = 19.2 ±
1.7 mm, N = 5) and M. zeylanica (mean SVL = 18.3 ± 1 mm, N = 3) were in between in body
size. The body sizes of the two cool-adapted montane isolates were smaller than the two warmadapted lowland dry zone forms; air temperature of the calling sites of M. karunaratnei and M.
zeylanica, the two montane isolates, were 19.1°C and 18.2°C respectively; the temperatures at
the two dry lowland habitat of M. mihintalei and M. ornata were 24.6°C and 25.2°C respectively. Temperature of the calling sites did not vary beyond ± 0.2°C across all recordings for
each of the species. This was because, for a given species, the recordings were made at a single
location within maximum of two consecutive nights. Results of the correlation analyses of all
call variables against SVL, temperature and body weight for the four species show that temperature of the calling site negatively correlate with call duration (ρ = -0.86), call rise time (ρ =
-0.88), 50% call rise time (ρ = -0.89) and pulses per call (ρ = -0.97), whereas SVL and body
weight negatively correlate with dominant frequency (ρ = -0.73, ρ = -0.70) and pulses per call
(ρ = -0.70, ρ = -0.78) respectively.
Hierarchical organizations of calls (i.e. call groups and call bouts) were not considered as
they vary widely across the recordings. For these species, calls were emitted as duets or in
groups. A single male always initiated calling following periodic pauses, which induced other
males to call; this was observed for all four species. Waveform, spectrogram and power spectrum of the most common call type (hereafter referred to as advertisement call) of the four
Microhyla species are illustrated in Fig 2. Pulsatile structure of the call, emitted as a short series
and the presence of a single prominent frequency band is common to all species (Fig 2). Frequency modulations were not observed in any species.
The advertisement call of M. karunaratnei contains between 50 to 95 pulses having an
average pulse rate of 77 pulses per second. The call duration ranged between 700 and 1172
¼ 866 101 ms). Call dominant frequency ranged between 3.1 and 3.4 kHz
ms. (X
(X ¼ 3:3 0:1 kHz). It takes an average of 661 ms to reach its maximum amplitude and
decreases rapidly within the next 205 ms. Call duration of M. zeylanica ranged between 1500
¼ 1852 123 ms). It contains 61 to 92 pulses having an averaged pulse
and 2000 ms (X
rate of 44 pulses per second. The call rises gradually within 1273 ± 243 ms and decreases
slowly over the last 575 ± 178 ms. The advertisement call of M. mihintalei and M. ornata
were short, less than half a second. Advertisement calls of M. mihintalei consist of 9 to 15
pulses, which had a rate of 58 pulses per second. Call duration ranged between 141 and 245
¼ 187 24 ms). Call typically reached its full amplitude under 144 ms
ms (X
¼ 80 30 ms) and decreased in amplitude over the last 106 ± 44 ms. Dominant fre(X
quency ranged between 1.3 and 2.6 kHz. Call duration of M. ornata was 300 ± 44 ms (210–
795 ms). It composed 9 to 14 pulses, having a pulse rate of 41 pulses per second. Dominant
frequency ranged between 2.2 and 3.4 kHz. Average call rise time and fall time were 154 ± 43
ms and 145 ± 61 ms respectively (Table 2).
Four temporal characters, call rise time, call fall time, 50% call rise time and 50% call fall
time of the four species show the highest variation within species (CV range between 19% and
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Fig 2. Advertisement calls of the four Microhyla species. (A) Ten second segment of a call by a single male. (B) Two second segment showing a
single call underlined in A. (C) Spectrogram of the call shown in B. (D) Power spectrum of the call averaged over the duration of each call depicted in B
(256 FFT size, Hanning window).
doi:10.1371/journal.pone.0159003.g002
86.4%), whereas other four characters, call duration, dominant frequency, pulse rate and pulses
per call were less variable, CV below 19% (Table 1).
The Principal Component analysis (Fig 3) on the correlations matrix, using four call property variables (Call duration, Dominant frequency, Number of pulses per call and Pulse rate)
from the four species shows that none of the species overlap in PC space. PC 1 axis explains
53% of the total variation, mostly by the number of pulses per call (factor score = 0.985) and
call duration (factor score = 0.874); PC 2 axis is explained by the pulse rate (factor score =
-0.805), which explains 25% of the variance. Microhyla zeylanica overlaps with M. karunaratnei in PC1 axis, but does not overlap with any other form in PC2 axis. Microhyla karunaratnei
slightly overlaps with both M. ornata and M. mihintalei in PC2 axis. Though M. ornata and M.
mihintalei are separate on the PC space, they overlap in both axes. Further the stepwise backward DFA (Fig 3) identified each species more than 99% as correct (100% of M. karunaratnei
and M. zeylanica and 99% of M. ornata and M. mihintalei, Wilks' lambda 0.0002); similar
results were obtained for the jackknifed dataset. Three discriminant functions were generated,
and eigenvalues of the first two variables were 59.09 and 15.76 respectively. The centroids are
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Table 2. Descriptive statistics for calls of the four Microhyla species based on values determined
from a sample of 100 calls from 5 males of each species (except M. zeylanica, 53 calls from 3 males).
Mean
SD
Range (min–max)
CV%
Microhyla karunaratnei
Call duration (ms)
866
101.7
699–1172
11.7
Call rise time (ms)
661
121.3
473–1009
18.3
Call fall time (ms)
205
40.6
112–306
19.8
50% Call rise time (ms)
353
113.5
199–763
32.1
50% Call fall time (ms)
44
13.6
16–92
31
Dominant frequency (kHz)
3.3
0.1
3.1–3.4
4.2
a
b
Pulses per call
66.5
14.2
50–95
14.4
Pulse rate
76.9
5.8
64.6–86.7
7.5
Microhyla zeylanica
Call duration (ms)
1852
123
1503–1999
6.6
Call rise time (ms)
1273
243
784–1634
19
Call fall time (ms)
575
178
157–979
31
50% Call rise time (ms)
527
169
204–802
32
50% Call fall time (ms)
70
27
18–141
38.6
Dominant frequency (Hz)
2.6
0.2
2.2–2.9
10.2
Pulses per call
84a
5b
61–92
6.8
Pulse rate (pulses/s)
44.5
3.2
37–49
7.1
Microhyla mihintalei
Call duration (ms)
187
24
141–245
12.8
Call rise time (ms)
80
29.9
44–144
36.8
Call fall time (ms)
106
44.2
35–199
41.4
50% Call rise time (ms)
27
11.2
14–53
40.6
86.4
50% Call fall time (ms)
26
22.7
3–79
Dominant frequency (kHz)
2.1
0.4
1.3–2.6
21.3
Pulses per call
13a
2.5b
9–15
10.3
Pulse rate (pulses/s)
58.6
2.8
49.8–66.1
14.0
Microhyla ornata
Call duration (ms)
300
57
210–795
19
Call rise time (ms)
154
43
47–207
28
Call fall time (ms)
145
61
75–675
42.4
50% Call rise time (ms)
31
7
19–46
23.2
50% Call fall time (ms)
34
18
3–89
52.5
Dominant frequency (kHz)
3.1
0.4
2.2–3.4
13.4
Pulses per call
13a
1b
9–14
8.2
Pulse rate (pulses/s)
41.6
1.5
36.8–44.9
9.6
a
Median instead of mean
b
Interquartile range instead of SD.
doi:10.1371/journal.pone.0159003.t002
3.27, 5.562 for M. karunaratnei, -6.132, 0.465 for M. mihintalei, -5.4, 3.746 for M. ornata and
15.588, -4.304 for M. zeylanica. The first canonical variable represents mostly call duration
(canonical discriminant function, CDF, 14.116), 50% call fall time (CDF 4.356) and call fall
time (CDF 3.325). The second canonical variable represents mostly 50% call fall time (CDF
6.478) and call fall time (CDF -2.386).
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Fig 3. The principal component analysis and the discriminant function analysis of call characters for the four Microhyla species. (A)
Plot of principle components 1 and 2 (PC1 vs. PC2) of the four call characters (call duration, dominant frequency, number of pulses per call
and pulse rate). (B) Canonical variables plot of the discriminant function analysis of eight call character variables with 95% confidence ellipses
and the centroids indicated.
doi:10.1371/journal.pone.0159003.g003
Discussion
All four species studied here have pulsatile calls, which also seem to be a characteristic feature
of the genus [26–33]. Hence the vocal repertoire within the genus is less complex when compared to other taxa studied from the region, such as most rhacophorids, ranids and bufonids
[9,14,20,39,40]. Most of the call characters can be explained in relation to phylogenetic relatedness and by habitat occupation. For microhylids, the phylogenetic relatedness seems to have
played a greater role than the habitat influence in the evolution of call characters [41].
Almost all members of the genus are pool breeders where the physical resources needed for
females are concentrated. The males advertising in choruses from such optimal habitats are
well known for Microhyla [26,29,31]. Choruses are also useful in several aspects such as
increasing attraction to females and reducing predation risk by finding refuge in numbers [1].
But the cost of calling is higher in choruses due to individual reproductive success; hence the
males make periodic pauses, which are essential to recover and conserve their energy.
A well-known strategy for adapting to increasing ambient temperature is shortening the call
duration and reducing the number of pulses [42,43]. This is evident for the cool-adapted M.
karunaratnei and M. zeylanica in having comparatively longer calls with higher number of
pulses when compared to the members inhabiting the warmer drier lowlands.
Among the four Sri Lankan species, M. mihintalei shows the highest within species variation
in all call characters except for call duration and call fall time. However wider comparisons cannot be done because most other studies have considered only a single individual.
Vocalization of M. karunaratnei and M. zeylanica were distinct from all others especially
having longer call durations where the call duration of all other members were below 0.85 s (S1
Table). In fact M. zeylanica has the longest call duration (1.5 to 2 s) among all microhylids.
Pulse rate of M. rubra from India has been reported as having the highest (108 pulses/s) among
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Bioacoustics of Sri Lankan Microhyla
the clade (S1 Table). This may have occurred as a result of following a different terminology
when characterizing the pulses. Microhyla petrigena is distinct within the group in having several unique characters such as the smallest in body size (SVL = 14 mm), highest dominant frequency (5100 Hz) and highest pulse rate (89 pulses/s). Call characters of M. ornata from India
are similar to that of the Sri Lankan population. Vocalization (call characters) of M. laterite
and M. sholigari are closer to the two Sri Lankan species M. karunaratnei and M. zeylanica
than to other members of Microhyla. Microhyla laterite, so far, has the highest number of
pulses per call among all congeners (S1 Table).
The only known locations of M. karunaratnei had been subjected to small-scale gem mining. These frogs however now are utilizing those abandoned gem pits, now overgrown with
vegetation, for breeding. It shows that they are somewhat adaptable to changing conditions.
Acoustic exploration of potential habitats can be used for rapid and accurate identification of
new populations of this cryptic frog.
Acoustic analysis made here facilitates the comparative understanding of vocalization for
the genus. Furthermore, this work will help non-destructive anuran surveys, identification of
new populations, population monitoring and behavioral experimentation.
Supporting Information
S1 Fig. Illustration of the eight call characters measured.
(JPG)
S1 Audio. Sample recordings of the advertisement call of Microhyla karunaratnei.
(ZIP)
S2 Audio. Sample recordings of the advertisement call of Microhyla zeylanica.
(ZIP)
S3 Audio. Sample recordings of the advertisement call of Microhyla mihintalei.
(ZIP)
S4 Audio. Sample recordings of the advertisement call of Microhyla ornate.
(ZIP)
S1 Table. Summary of the common call characters of the members representing the genus,
Microhyla that have been studied so far.
(DOCX)
Acknowledgments
The authors thank the following individuals and institutions for contributions to this paper:
Rafael Marquez and an anonymous researcher for reviewing and suggesting improvements;
Gayani Senevirathne for providing feedback to improve the paper; Mark Bee, SD Biju and
Robin Suyesh for helping with refining bioacoustics techniques and training of analysis; Gayani
Senevirathne, Nuwan Karunarathne and Champika Bandara for data collection and field work;
the Department of Wildlife Conservation of Sri Lanka and the Forest Department of Sri Lanka
for research permits.
Author Contributions
Conceived and designed the experiments: MM NW. Performed the experiments: NW MM.
Analyzed the data: NW MM. Contributed reagents/materials/analysis tools: MM NW. Wrote
the paper: MM NW.
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