In the following we briefly analyze and compare voice of several races of Chestnut-capped Brush-finch (Arremon brunneinucha). 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).
Our main interest is to compare voice of race apertus with other races, as the former has been suggested to represent a distinct species (Navarro-Sigüenza et al. 2004).
We have found only a single recording of song for race apertus, to be compared with geographically closest race brunneinucha (illustrated with multiple sonograms in the pdf version of this note): there seem to be no obvious differences in song.
As a matter of fact, differences of Mexican races vs other races are more outspoken, e.g. Costa Rica/Panama highlands (elsae) : shorter, simpler phrases with narrower freq. range, and South America, where there is quite some variation within wide-spread race frontalis, but notes on average cover a narrower frequency range.
We can thus conclude that song of race apertus is not markedly different from its neighboring race, but at the other hand there seems to be a slight change in voice south of the isthmus of Tehuantepec, with song covering a narrower frequency range and note shapes somewhat less steeply changing pitch (lacking the multiple 'vertical lines' on a sonogram). A more detailed analysis would be required to have a better quantification of this vocal change.
This note was finalized on 25th May 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.
Navarro-Sigüenza, A.G. & Peterson, A.T. (2004). An alternative species taxonomy of the birds of Mexico. Biota Neotropica 4(2): 1–32.
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: on360_chestnut-capped_brush-finch.pdf