Boophis ankarafensis

behaviour · bio.acousti.ca

Vocalisations of Boophis ankarafensis sp. n. were recorded on thirteen occasions between October 2011 and January 2012. No males were found in calling activity between January and February 2013 (later in the wet season). Calls were detected from just 8 of the 37 locations monitored on the peninsula (Fig. 4). All eight of these locations were along the banks of a single stream in Ankarafa Forest. Vocalisations were detected within 3978 minutes of acoustic recordings and averaged 306 ± 181 minutes per night (n = 13). A total of 59.8% of these minutes contained vocalisations emitted by a single male caller, with the remainder emitted as a chorus of two or more callers. Total activity equalled 5576 minutes and average per night activity amounted to 429 ± 273 minutes (n = 13). Levels of calling fluctuated throughout the night (Fig. 5); there was a peak in activity just after dusk, followed by a slow decline until dawn, when the fewest vocalisations were detected (y = 0.019e-0.015x; R2 = 0.582). The acoustic repertoire consists of two note types: a multi-pulsed trill (type 1; Fig. 6A) and a 1-3 pulsed click (type 2; Fig. 6B). Only 11 of the 13 occasions produced recordings of a sufficient audio quality to perform spectral analysis. Measurements were taken from five representative notes of each call type per night, thus a total of 55 trill notes and 55 click notes were measured (Table 3). From a subset of five trill notes, acoustic parameters were measured for ten sequential broadband pulses and ten sequential narrowband pulses per note. The environmental temperature of the recorded trill notes ranged between 25.2 and 30.3 °C (27.4 ± 1.08 °C, n = 55) and of the click notes between 22.9 and 29.7 °C (26.7 ± 1.41 °C, n = 55). The trill note measured 4.29 ± 1.29 s (1.614–8.091 s, n = 55) and is composed of alternating broadband and narrowband pulses. These notes had a broadband pulse rate of 15.0 ± 1.19 pulses/s (11.7–17.3 pulses/s, n = 25) and peak frequency of 4.14 ± 0.131 kHz (3.69–4.48 kHz, n = 55). Broadband pulses measured 3.47 ± 0.485 ms (2.50–5.06 ms, n = 50) whereas narrowband pulses were slightly longer at 17.9 ± 2.56 ms (11.2–25.1 m; n = 50). The broadband pulse had a peak frequency of 4.19 ± 0.122 kHz (3.91–4.34 kHz; n = 50), whereas the narrowband pulse measured 4.15 ± 0.108 kHz (4.00–4.31 kHz, n = 50). Bandwidths were 0.288 ± 0.169 kHz (0.120–0.780 kHz, n = 50) for the broadband pulse compared to just 0.155 ± 0.036 kHz (0.129–0.280 kHz, n = 50) for the narrowband pulse when measured at a -10 dB threshold. The majority of click notes consisted of two pulses, although singular and triple pulses were also observed. Click notes had a total duration of 52.9 ± 5.20 ms (40.0–68.7 ms; n = 55) and peak frequency of 3.95 ± 0.162 kHz (3.57–4.30 kHz; n = 50). Bandwidth of the click note measured 0.538 ± 0.234 kHz (0.120–0.143 kHz) at a -10 dB threshold. The advertisement call of Boophis ankarafensis sp. n. sounds similar to that of the morphologically similar Boophis bottae; with both species possessing a trill note and a click note in their acoustic repertoires (Vences et al. 2006; Rosa et al. 2011). However, a number of differences can be used to distinguish them. In our comparison with Boophis bottae we selected only those notes recorded at a similar ambient temperature, and we have also distinguished the two pulse types of the trill by their relative differences in bandwidth, rather than duration as used by Vences and Glaw (2002); the broadband pulse and narrowband pulse of Boophis ankarafensis sp. n. are equivalent to the shorter and longer duration pulses of Boophis bottae respectively. The trill note (type 1) of Boophis ankarafensis has a faster broadband pulse rate than the trill of Boophis bottae (13.4–13.5 pulses/s, 25.2 °C versus 8.12–11.6 pulses/s, 23.0 °C). The click note (type 2) of Boophis ankarafensis sp. n. usually contains just two pulses, and only rarely consists of three, in contrast the click notes of Boophis bottae are usually three-pulsed. Although only slightly divergent, it is discernable that the spectral frequency of the click note is lower in Boophis ankarafensis sp. n than in Boophis bottae (3.75–3.84 kHz, 22.9 °C versus 4.23–4.42 kHz, 23 °C). The trill note of Boophis ankarafensis shows a slightly lower broadband pulse peak frequency (4.10–4.24 kHz, 25.2 °C versus 4.30–4.64 kHz, 23 °C) but a similar narrowband pulse peak frequency (4.18–4.31 kHz, 25.2 °C versus 4.23–4.42 kHz, 23 °C) in comparison to Boophis bottae.

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