The call of Rhinella festae (Peracca, 1904) (Anura: Bufonidae) from Morona Santiago, Ecuador

ABSTRACT

We describe for the first time the call of Rhinella festae (Peracca, 1904), recording it in captivity inside a plastic bag. The call is composed of 1 to 2 multi-pulsed notes (2–5 pulses), has an average duration of 0.72 s, and a dominant frequency of 1.40 kHz. This species is characterized by the absence of vocal slits and sacs, so the emission of this call would be considered unusual and uncommon. In addition to the purpose of improving the knowledge of species suggested as mutes, we have also compiled information from other anuran species that emit sounds with the absence of these anatomical structures.

KEYWORDS:

• Acoustic communication
• vocal slits
• vocal sacs
• mute
• ex situ

Rhinella festae is a nocturnal species that is assigned to the Rhinella festae species group that inhabits the undergrowth of tropical and piedmont primary forests [1–3]. This species is distributed in middle and low elevations, up to 1700 m in the Cordillera de Kutukú and Cordillera del Cóndor in Ecuador and Peru [4,5].

One of the most conspicuous and important ethological features of anurans is their acoustic communication [6,7]. Anuran species have different types of calls, which express a wide variety of behaviours and are associated with a specific social context and function [8–11]. Anuran calls present specific characteristics for each species (i.e. spectral and temporal parameters), being used in the herpetology as an identification trait [6,12,13].

The call of Rhinella festae is a particularly unusual record because this species has no vocal slits and sacs [4], anatomical structures that are related to the sound production mechanism in anurans [7,14]. In this work, we present for the first time the call of Rhinella festae after remaining unknown more than 100 years later of its description as a new species.

Recordings were made on 26 November 2016 in the locality Rio Abanico (2° 13’ 25”S, 78° 14’ 45”W, datum WGS84, 1,570 m.a.s.l), at the province of Morona Santiago, Ecuador, at 18:00 h (16°C, 85% relative humidity). One male was unexpectedly recorded in captivity several hours after being collected while emitting calls from inside a plastic bag (ex situ) in a base camp. Calls were obtained using an Olympus WS-802 digital recorder about 1 m distance from the specimen. Calls were analyzed at a 44.1 kHz sampling rate and 16–bit resolution. The collected male was deposited at the División de Herpetología del Instituto Nacional de Biodiversidad, Quito, Ecuador (DHMECN 15830; SVL 34 mm). The recording was deposited at the Fonoteca Zoológica (www.fonozoo.com) del Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain (FZ sound code 12,022).

For the analysis of the calls, we used Raven Pro version 1.4 [15]. In the settings, we applied a Hann window with 50% overlap and a DFT window width of 512 samples. Oscillogram and spectrogram images were obtained using R software version 3.6.3 [16], with the package Seewave version 2.1.5 [17] using a Hanning window type with 90% overlap, a fast Fourier transform (FFT) window width of 1024 samples, and a frequency limit of 4 kHz. Audio files in WAV format were imported with the tuneR package version 1.3.3 [18]. Definitions, terminology, and measurements in the description of the call follow Köhler et al. [11] and Sueur [19].

The call of Rhinella festae is composed of 1 to 2 multi-pulsed notes (2–5 pulses), with a mean dominant frequency of 1.40 kHz. The lowest dominant frequency values occur in the last pulses of the notes (Figure 1). We report the spectral and temporal parameters in Table 1. The analyzed calls were not assigned to a specific call type (see Toledo et al. 2015 [10]). They could tentatively be classified as advertisement calls, as these are most common in anurans [7,11]. Considering the low number of samples and the special condition of recording (i.e. calls emitted from inside a plastic bag). The calls of Rhinella festae analyzed in this report could not be considered like common of this species, because their calls in natural environments are not known.. The emissions of an individual in captivity may vary. Under this context, Batallas and Brito [20] described the advertisement call of Noblella lochites (Lynch, 1976) and mentioned that it is clearly different from calls recorded in captivity.

Table 1. Descriptive statistics of call parameters of one individual of Rhinella festae.

Parameters	Range (Mean ± SD)
Dominant frequency (kHz)	1.21‒1.55 (1.40 ± 0.10)
Call duration (s)	0.18‒0.98 (0.72 ± 0.29)
Interval between calls (s)	1.87‒29.45 (6.55 ± 7.95)
Call rate (calls/min)	1.98‒27.60 (14.29 ± 7.91)
Notes per call	1‒2 (1.75 ± 0.45)
Note duration (s)	0.14‒0.29 (0.22 ± 0.04)
Interval between notes (s)	12‒26 (18.75 ± 3.37)
Note rate (notes/s)	1.20‒1.58 (1.47 ± 0.12)
Pulses per note	2‒5 (3.86 ± 0.79)
Pulse duration (s)	0.011‒0.058 (0.024 ± 0.01)
Interval between notes (s)	0.022‒0.061 (0.041 ± 0.01)
Pulse rate (pulses/s)	11.63‒19.61 (14.91 ± 1.81)

Figure 1. Oscillogram and spectrogram of the call of a male individual (DHMECN 15830; SVL 34 mm) of Rhinella festae, recorded in the locality Rio Abanico, Morona Santiago province, Ecuador.

The call of R. festae is the first known and described call for the Rhinella festae species group. The unusual emission with the absence of vocal slits and sacs is not a characteristic and unique trait of R. festae, and it also occurs in other species of anurans (Table 2). One example to be noted is the case of Chiasmocleis antenori (Walker, 1973), in which Duellman [21] suggested that it must be a mute species due to the absence of these anatomical structures. However, the genus Chiasmocleis have been described the calls of this and several species that are characterized by the absence of vocal slits and sacs (Table 2).

Table 2. Studies that report call descriptions with absence of vocal slits or sacs in anurans

Species	Vocal slits	Vocal sac	Type	Reference
Chiasmocleis antenori	Absent	Absent	Quantitative*	[23]
Chiasmocleis carvalhoi	Absent	Absent	Quantitative	[24]
Chiasmocleis mantiqueira	Absent	Absent	Quantitative	[25]
Chiasmocleis parkeri	Present	Absent	Quantitative	[26]
Craugastor aff. Persimilis	Absent	Absent	Quantitative	[27]
Craugastor gabbi	Absent	Absent	Quantitative	[27]
Craugastor galacticorhinus	Absent	Absent	Qualitative**	[28]
Craugastor gollmeri	Absent	Absent	Quantitative	[29]
Craugastor noblei	Absent	Absent	Quantitative	[30]
Craugastor stejnegerianus	Absent	Absent	Quantitative	[31]
Craugastor stejnegerianus	Absent	Absent	Quantitative	[27]
Craugastor underwoodi	Absent	Absent	Quantitative	[27]
Craugastor yucatanensis	Absent	Absent	Quantitative	[32]
Gastrotheca cornuta	Absent	Absent	Qualitative	[33]
Megaelosia goeldii	Absent	Absent	Qualitative	[34]
Pristimantis dorado	Absent	Absent	Quantitative	[35]
Pristimantis nelsongalloi	Absent	Absent	Quantitative	[36]
Pristimantis paquishae	Absent	–	Quantitative	[37]
Pristimantis trachyblepharis	Absent	Absent	Qualitative	[38]
Rhinella festae	Absent	Absent	Quantitative	This study
Stefania evansi	Absent	Absent	Quantitative	[33,39]
Stefania riveroi	Absent	Absent	Quantitative	[33,39]
Triprion spinosus	Absent	–	Quantitative	[40,41]

*Based on an analysis of the spectral and temporal parameters of calls.

**Based on comments and onomatopoeia of sounds.

Rhinella festae is an uncommon species in Ecuador, and the current state of its population is unknown [4,22]. Describing the call of this species will not only generate an identification trait, but it will allow with passive acoustic methods (knowing beforehand that it emits sounds and is not mute) to monitor and expand the knowledge of this species.

Acknowledgments

We thank Cecilia Ortega (Ecotono) for the facilities provided during fieldwork. We are very grateful to Claudia Koch, who generously revised and provided suggestions on an early version of this manuscript. We thank three anonymous reviewers for their valuable and constructive comments that helped improve the manuscript. We thank Ministerio del Ambiente de Morona Santiago for research permit N°. 11–16–IC–FLO–FAU–B–DAPMS/MAE.

Disclosure statement

No potential conflict of interest was reported by the author(s).