In the following we briefly analyze and compare voice of the different races of Bay Wren (Thryothorus nigricapillus). 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. nigricapilus 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.
Some examples of duet (illustrated with multiple sonograms in the pdf version of this note): Northern group (W Panama) and Southern group (W Ecuador).
From the above examples, it would appear that northern birds have a song covering a larger frequency range (c. 4.5 - 7kHz) vs southern birds (c.3-4.5kHz). Recordings from Colombia are however somewhat intermediate: Antioquia, Colombia: freq. range c. 5kHz and Cali, Colombia: freq. range c. 5.5kHz. This vocal difference may thus be rather clinal from North to South.
Other parameters such as # notes/phrase, phrase duration, note length etc. don't show clear differences, given the broad range of variation.
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: on293_bay_wren.pdf