In the following we briefly analyze and compare voice of the different races of Japanese Bush-warbler (Cettia diphone). 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 the different vocalizations per subspecies (illustrated with multiple sonograms in the pdf version of this note):
borealis: song, alternative song and call
cantans: song, alternative song and call
Comment: there is a small breeding population of cantans in S South K, which seems to be parapatric with borealis/canturians, split as Manchurian Bush Warbler (Kennerley et al. 2010). IOC at the other hand seems to call Manchurian Bush Warbler only the race borealis.
restricta: song, alternative song and call
canturians: song (recording from the Shanghai area mid May, could be borealis on migration as well??), song (these should be true canturians)
The situation is less simple then one may deduct from the description by Kennerley et al. (2010). cantans and restricta are similar for a number of reasons:
* song starts either with a continuous whistle at about 2kHz or a lower-pitched whistle which usually starts continuously and changes to a limited number of repeated notes.
* the second part of the song is very variable, but max. freq. of the highest note is 3-5kHz
* they both have an alternative song which consists of 2-3 notes up and down repeated for long period
* they both have a short, dry "tzhik" call
borealis differs from cantans/restricta for the following reasons:
* song starts always with a long series of short notes at about 1kHz (never continuous whistle)
* the second part of the song is very variable, but max. freq. of the highest note is higher than 5kHz
* there is seemingly an alternative song, but doubled note is given without any intermediate space, thus sounding rather like a single note repeated
* call (not much recording available) is given at faster pace, rather like short rattles
diphone (only 2 recordings available) fits with cantans/restricta (max. freq. highest note, continuous whistle changing to separate notes)
canturians (only a few certain recordings) fits with borealis (max. freq. well above 5kHz, intro whistle at 1kHz and mainly sequence of short notes).
(we have found no recordings of riukiuensis)
We can thus compare group cantans/restructa/diphone/riukiuensis vs.group borealis/canturians, the latter lacking a higher-pitched continuous whistle (score 1-2), reaching higher frequencies in 2nd part of song (score 2), having a more monotonous alternative song (score 1-2), and having a faster-paced almost rattling call note (score 2).
When applying Tobias criteria, this would lead to a total vocal score of about 4.
This note was finalized on 3rd March 2016, using sound recordings available on-line at that moment. We would like to thank in particular the many sound recordists who placed their recordings for this species on XC.
Kennerley, P.R. & Pearson, D. (2010). Reed and Bush Warblers. Helm Identification Guides. Christopher Helm, London.
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: on254_japanese_bush-warbler.pdf