In the following we briefly analyze and compare voice of the two races of Gray's Warbler (Locustella fasciolata). 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 of both races is structurally similar, a loud explosive phrase starting with a few staccato notes quickly accelerating into a descending stuttering warbled finish. Some examples of song (illustrated by sonograms in the pdf version of this note): amnicola and fasciolata.
Voice of both races can be separated e.g. by the difference in pace and total length of song phrase. amnicola typically has a song phrase duration of c. 2.2 - 3.4s vs 1.5 - 2.2s for fasciolata, both with roughly the same number of notes (8-12) resulting in a marked difference in pace. If we consider song length and pace as independent variables, then application of Tobias criteria would lead to a score of at least 2+2 =4.
These findings concur with the vocal differences noted in Kennerley et al. (2010).
This note was finalized on 12th February 2016, using sound recordings available on-line at that moment. We would like to thank in particular the sound recordists who placed their recordings for this species on XC: Peter Boesman, Klaas Jachmann, Frank Lambert and Anon Torimi.
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: on234_grays_warbler.pdf