In the following we briefly analyze and compare voice of the different races of Brownish-flanked Bush-warbler (Cettia fortipes). 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).
Song is structurally similar to e.g. Cettia diphone but higher-pitched: a long pure whistle (sometimes preceded by a single or several short notes) followed by a short loud phrase of several different notes. Our main interest is to compare the Taiwanese race with the mainland races. An overview (illustrated with multiple sonograms in the pdf version of this note):
Other races (from west to east): Pakistan, India, Vietnam, China
It is clear from the above examples that vocal variation of robustipes falls well within the range of other races. All basic sound parameters (note length, frequency, # of notes..) are about the same. One minor difference seems to be that robustipes reaches on average lower frequencies in the song phrase (with considerable overlap): 1600 - 1900Hz (n=7) vs 1600 - 2500Hz in other races (n=15)(score 1).
Vocal differences are thus very small.
This note was finalized on 2nd November 2015, 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:
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: on255_brownish-flanked_bush-warbler.pdf