In the following we briefly analyze and compare the voice of the different races of White-browed Shrike-babbler (Pteruthius flaviscapis). 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 online at Xeno Canto (XC).
Voice had already been analyzed in Rheindt & Eaton (2009), and was part of the evidence to split this complex as four BSC species. If we score vocal differences based on the measurements of voice (Table 3 p. 36, based on 30 recordings of eight races, which is quite small), by applying Tobias criteria, we get:
* ripleyi: vs. validirostris: score 2 based on longer intra-motif breaks, but score 0 vs. two other groups.
* annamensis: shorter intra-motif breaks vs. aeralatus, but as this is part of group ‘Blyth’s’, comparison with overall group gives score 0. Score vs. ripleyi about 1 and vs. flaviscapis score 0.
* flaviscapis vs. Blyth’s group: score 0
Considering the limited number of samples, the wide variation of measurement results within recordings of the same race, and the minimal differences identified, the stated conclusions on vocal differences are rather weakly supported by data and, at least within the framework of quantification by application of Tobias criteria, vocal differences fall in the category ‘minor’.
Since publication of this study, quite a few additional recordings have become available on XC. Some confirm the statements in the above paper, e.g. nominate flaviscapis: the rhythmic 1+2 phrase continues to be seemingly the only song variant, with occasionally a 1+3 motif.
Others weaken the statements in the aforementioned study, e.g. the claimed ‘dramatic vocal break’ between slow singing ripleyi vs. fast singing validirostris can no longer be maintained, as can be seen from the following sequence of sonograms (in the .pdf version of this note) from west to east, or the vocal divergence of ‘Da Lat Shrike-babbler’ annamensis vs. ‘Blyth's Shrike-babbler’ now showing considerable overlap.
With more recordings gradually becoming available, it would seem there is need for a thorough new vocal analysis, which investigates a higher number of (possibly more complex) parameters such as, e.g., average delivery of x+y motifs (annamensis often utters a 2+3 or 2+4 song, flaviscapis 1+2) etc. Nevertheless, given that there is little difference in the basic sound parameters, it seems unlikely that scoring according to Tobias criteria will lead to scores higher than 3 in pair-wise comparisons, and scores of any group vs. all other groups will obviously be lower.
This note was finalized on 30th January 2016, using sound recordings available online at that moment. We would like to thank in particular the many sound recordists who placed their recordings for this species on XC.
Rheindt, F.E. & Eaton, J.A. (2009). Species limits in Pteruthius (Aves: Corvida) shrike-babblers: a comparison between the Biological and Phylogenetic Species Concepts. Zootaxa 2301: 29–54.
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: on165_white-browed_shrike-babbler.pdf