In the following we briefly analyze and compare voice of the two races of Long-billed Wren (Thryothorus longirostris). 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).
Just like some other members of this genus, T. longiostris has a 'short song' consisting of a short phrase of one or a few notes repeated at intervals, and a synchronous duet song in which both members of a pair sing continuously over a longer period. The latter is heard much less than the 'short song'. An overview of vocalizations per race (illustrated with multiple sonograms in the pdf version of this note): bahiae (Short song and duet song) and longirostris (Short song and duet song).
Both races show quite some variability in song. Short song of bahiae on average consists of simpler notes, typically 1-3 notes vs 2-6 notes in longirostris. Duet song of both races is quite similar, with basic sound parameters about the same: phrases consist of 2-6 notes, with phrase length quite variable, frequency range is similar, with especially in bahiae a very wide range. A larger set of recordings would be needed to prove consistent differences, if any. All in all, vocal differences between the two races seem to be quite minor.
Based on a slight difference in short song (average number of notes) a vocal score of 1-2 could be given.
This note was finalized on 15th April 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.
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: on292_long-billed_wren.pdf