In the following we briefly analyze and compare voice of the different races of Russet-crowned Warbler (Basileuterus coronatus). 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).
An overview of song per race (illustrated with multiple sonograms in the pdf version of this Note): regulus, Colombia, Ecuador (excl. castaneiceps/chapmani), castaneiceps/chapmani, N Peru (inaequalis), coronatus, S Peru, notius.
Geographical variation of song is rather complex. It would seem that especially song at the two extremes of the range has evolved in a rather similar direction, compared to the races in the central part of its range: regulus in the north has clearly higher-pitched staccato notes in the first part of its song, and a distinct fairly long trill at the end. notius and to a lesser extent coronatus have developed a similar song. On the contrary, birds from Colombia S to N Peru (incl. castaneiceps/chapmani) have a lower-pitched song with longer notes, sounding more melodious and at a slower pace.
A more in depth analysis would be required to unveil all consistent differences that exist among the various races, as the situation is clearly more complex than simply white-bellied vs yellow-bellied birds, given that the former group (castaneiceps and chapmani) does not differ substantially in song from adjacent races.
This note was finalized on 27th June 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: on378_russet-crowned_warbler.pdf