In the following we briefly analyze and compare voice of the different races of Spotted Towhee (Pipilo maculatus). 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).
There are apparently no recordings available of race socorroensis from Socorro Island.
Song of the other races is quite variable, but typically consists of a few introductory notes followed by a trilled series of identical notes. The main difference in song seems to be between Pacific birds (which lack introductory notes, or just utter a single note without pause linked to the trill) and the other races. (Illustrated with sonograms in the pdf version of this note: Pacific (from Oregon to Baja California coastal races) and other races).
There are also vocal differences in the main call note: Southern races (Olive-backed group) utter a piercing upslurred buzzy note not shared by other races (examples from Guatemala (repetens), S Mexico (oaxacae), Distrito Federal (macronyx) and Chiapas (chiapensis). All other races utter a nasal call. In Pacific birds, call is mainly rising while for interior birds the call is usually overslurred, but there is seemingly quite some overlap.
The difference in call note can be quantified and scored based on min. frequency, max. frequency of the base harmonic, freq. range (bandwidth) of the base harmonic (or end. freq. minus start freq.) or number of harmonics. Although this is not the primary vocalization, scoring would lead to a vocal score of about 4.
Note that vocal difference vs Eastern Towhee P. erythrophthalmus is also mainly the call rather than song. These are clearly closer to the Olive-backed group (see examples).
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.
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: on363_spotted_towhee.pdf