In the following we briefly analyze and compare voice of the different races of Common Scaly Thrush (Zoothera dauma), and Sri Lanka Scaly Thrush (Zoothera imbricata). 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).
An overview of song per race (illustrated with sonograms in the pdf version of this note):
aurea/toratugumi: Song is a drawn-out whistle at flat pitch (or slightly descending), given at intervals (even on the small distant islands such as Ogasawara and Haha-Jima far south of the Japanese mainland).
major: Song consists of a sequence of well-spaced different short phrases, which typically include 1-2 rich low-pitched throaty whistles, sometimes combined with a short high-pitched note.
dauma: Song of nominate described as a rather rapid but disconnected series of abrupt, simple, rich notes mixed with squawks, e.g. “pur-loo-trii-lay [repeated] dur-lii-dur-lii [repeated twice] drr-drr-chew-you-wi-iiii [repeated]”, sometimes a more languid, continuous stream of notes of same type, “chirrup chwee chueu weep chirrol chup” (HBW Alive, Collar 2013). This description may be based on the single recording we have found (ML169652). A sonogram depicted in Ripley's guide (Rasmussen et al. 2012) is slower-paced, and the corresponding voice description says: A varied but halting series of short, abrupt, simple disconnected, near-vertical notes, some clear and slurred, some rich and/or burry, others squawking and unmelodious (some combine above qualities, but usually have only 1-3 elements) (pitch 1.5 - 4kHz, note duration 0.1 - 0.3s, 0.5-2 notes/s (suggesting a closer resemblance to race major).
neilgherriensis: Voice apparently 'never directly reported' (Rasmussen et al. 2012)
horsfieldi: Voice is said to be 'a soft monotonous whistle' (MacKinnon et al. 1993), but it is not clear if this is based on the song of birds in that region.
imbricata: Song is a drawn-out slightly down-slurred whistle (duration 0.7-08s, 2.3-2kHz). We have only found a single recording (Warakagoda et al. 2008).
breeding population Taiwan (race ???): Based on the following recording from June, presumably resident population has a song consisting of a drawn-out whistle at flat pitch.
From the above, it is clear that vocally there are several distinct groups, but given that voice of several races is basically unknown, the picture is incomplete.
It would seem that vocally, major and dauma are the most distinctive races (both have a song consisting of complex notes vs. the simple whistle of other races (which results in a score 3-4 for larger freq. range, a score 3 for # of different notes, etc.). In between these two taxa, differences are smaller, but with only 1 available recording (and two somewhat different descriptions) of dauma difficult to assess. It would appear that major has more separated phrases of a few notes, which are more complex, but this is highly speculative.
Song of the breeding population in Taiwan is about identical to aurea/toratuguma.
imbricata is slightly different from aurea/toratuguma, in having a down-slurred start of every whistle (but birds in Japan also have occasionally down-slurred whistles, e.g. XC200561, XC285231, XC372117) (at most score 2 for larger freq. range).
neilgherriensis and horsfieldi lack information on voice.
This note was finalized on 19th April 2016, using sound recordings available on-line at that moment (and update July 26th 2017 with info about small Japanese islands). We would like to thank in particular the many sound recordists who placed their recordings for this species complex on XC.
Collar, N. (2016). Common Scaly Thrush (Zoothera dauma). 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/58349 on 19 April 2016).
MacKinnon, J. & Phillipps, K. (1993). A Field Guide to the Birds of Borneo, Sumatra, Java and Bali. Oxford University Press. Oxford, New York and Tokyo.
Rasmussen, P.C. & Anderton, J.C. (2012). Birds of South Asia. The Ripley Guide. Second Edition. Lync Edicions. Barcelona.
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.
Warakagoda, D. & Hettige, U. (2008). Birds of Sri Lanka. MP3 sound and image collection. Birdsounds.nl. The Netherlands.
More Information: on300_common_scaly_thrush.pdf