In the following we briefly analyze and compare voice of the different races of Slender-billed Cicadabird (Coracina tenuirostris). We also try to quantify the extent of any vocal differences using the criteria proposed by Tobias et al. (2010), as a support for taxonomic review. We have made use of sound recordings available on-line from Xeno Canto (XC), Macaulay Library (ML) and Avian Vocalizations Center (AVoCet).
With thirty(!) subspecies, many confined to single islands, this is obviously a complex case, and this note should rather be seen as a preliminary analysis. An overview of the different races (of which we have already grouped a few based on morphology and distribution)(illustrated by many sonograms in the pdf version of this note):
E. t. monacha: A quiet, upslurred whistle, variable, sometimes louder and repeated in song-like fashion (HBW, Taylor 2016). Confirmed by 4 available recordings.
E. t. nesiotis: Voice includes a quiet, upslurred whistle (like monacha), often given in pairs, and quiet, somewhat complaining phrases of 3-4 notes rapidly repeated (based on a single available recording).
E. t. insperatum: Cat-like whistles and low churrs, rolling “preeer” and short “chip-chip-breer” (HBW, Taylor 2016). Confirmed by 6 available recordings, mainly nasal cat-like overslurred whistles, given either leisurely more or less drawn-out, or in fast and loud chattering series, occasionally, a rolling rising “preeer” or "prueeur", and a subdued, short “chip-chip-breer”.
E. t. pelingi: Presumed song a repeated double downslurred note, the second slightly lower-pitched, sounding quite strident "chee-che...chee-che..." (based on a single recording).
E. t. grayi: Voice includes: a burry slightly rising drawn-out rattle (slightly longer in Morotoi, shorter with intro note in Halmahera, c. 1.5s versus c. 1.0s ), and short sharply rising fairly mellow "wit", sometimes given in series (Morotai) (sounding quite like some notes of monacha, but distinctly different on sonogram being polyphonic).
E. t. obiense: Only a single recording available. Voice includes a burry drawn-out rattle at flat pitch about 0.9s long (marginally shorter than in Halmahera and lacking a clear intro note), short sharply rising fairly mellow "wit" (about identical to grayi) sometimes given in a rapid series sounding harsher. (Overall quite similar to grayi)
E. t. meyerii (+ numforanum): A single recording available of numforanum. Presumed song is a repeated overslurred whistle, about 0.6s long and sounding quite burry, especially towards the end.
E. t. admiralitatis: In Admiralty Is (admiralitatis) a repeated downslurred “seeu” (HBW, Taylor 2016). No recordings available. HBW description may or may not match the song of remotum group...
E. t. remotum (+ [below barred]: matthiae, heinrothi, rooki, nisorium, + [below unbarred]: ultimum, saturatius, erythropygium Based on 11 recordings, voice includes presumed song, a long series of pure whistles, either upslurred or downslurred (saturatius, erythropygium), a chattered series of notes without harsh timbre (saturatius, erythropygium), doubled or tripled notes sounding like short chatters (saturatius), a short upslurred "wit" call (heinrothi) quite like grayi. A recording from Choiseul island is quite unusual (ML202665), a burry whistle (somewhat like meyerii group) but this may well be Solomons Cuckoo-shrike C. holopolia !?
E. t. rostratum: No recordings available.
E. t. tenuirostre + [A] edithae, pererratum, emancipatum, kalaotuae, timoriense + [B] amboinense, nehrkorni, muelleri, aruense, tagulana, melvillense: Presumed song a long repeated series of notes, either very burry (cicada) or pure whistled (tenuirostris), or similar or notes slightly bisyllabic (muelleri), or much slower and much more nasal (melvilense/tenuirostris).
From the available recordings, which in many cases are just a few, it would seem that:
monacha has a limited vocabulary closest to nesiotis, which seems to have a slightly more extensive vocabulary. Both differ from all other groups by the mellow (mono-phonic) upslurred whistles.
insperatum is unique in having nasal cat-like whistles and a high-pitched ringing rising whistle.
pelingi is unique in having a simple song consisting of a repeated double downslurred note.
grayi and obiense are vocally very similar. More recordings would be needed to determine whether there are any consistent differences.
meyerii group seems also to have a unique song, a slowly repeated burry overslurred whistle.
admiralitatis: based on description, may well be very close to remotum group.
remotum group is close to tenuirostre group, but seems to exclusively utter a song of rapidly repeated upslurred or downslurred whistles , while the latter has a very variable song.
tenuirostre is vocally the most diverse group, also within the single race tenuirostre, and with so many races lacking any recordings, it is too early to say whether there are more vocally distinct groups in here.
While these findings all need to be confirmed by many more recordings when these become available, we could very tentatively score:
monacha vs. nesiotis: score 1, these two versus all others at least 2
inesperatum: at least 2 versus all others
pelingi : at least 2 versus all others
grayi vs. obiense: score 0-1, at least 2 versus all others
meyerii group: at least 2 versus all others
admiralitatis vs remotum group: possibly 0 (?), these two versus tenuirostre group: score 1
This note was finalized on 5th February 2016, using sound recordings available on-line at that moment. We would like to thank in particular the sound recordists who placed their recordings for this species on XC, ML and AVoCet: Marc Anderson, Patrik Åberg, Alexandra Class, Scott Connop, Bram Demeulemeester, Pratt Douglas, Phil Gregory, Emma Greig, Frank Lambert, Niels Krabbe, Greg McLachlan, John Mittermeier, John V Moore, Mike Nelson, Mark Robbins, Marc Thibault, Mark Todd, Colin Trainor, Bas Van Balen and Adrian Walsh.
Taylor, B. (2016). Slender-billed Cicadabird (Coracina tenuirostris). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/57864 on 5 February 2016).
Tobias, J.A., Seddon, N., Spottiswoode, C.N., Pilgrim, J.D., Fishpool, L.D.C. & Collar, N.J. (2010). Quantitative criteria for species delimitation. Ibis 152(4): 724–746.
More Information: on180_slender-billed_cicadabird.pdf