In the following we briefly analyze and compare voice of the two races of Black-capped Sparrow (Arremon abeillei). 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).
A comparison of song (illustrated with multiple sonograms in the pdf version of this note): A.a. abeillei and A.a. nigriceps.
In both races, song consists of two parts: part 1 is a sequence of 2-4 notes, often alternating rising and falling but sometimes just all identical notes, part 2 (only in a few cases not present) is a more rapid series of repeated identical notes.
There is quite some variability in song, and differences between the two races are rather subtle, but they can be safely told apart because of part 2: abeillei has notes in part 2 which are sharply decreasing in pitch and which cover a large frequency range (bandwidth c. 5-7kHz). nigriceps has notes in part 2 which are rising in pitch (or occasionally sharply overslurred) and which have a smaller frequency range (c. 2-4kHz).
The difference in frequency range of part 2 (over 5000Hz for abeillei vs around 3000Hz for nigriceps) would lead to a score of at least 2, with notes rising in nigriceps (1-2). Another difference seems to be that the total length of the (full) song is on average shorter in abeillei (less than 2s vs over 2s for nigriceps (due to the repeated notes of part 2 delivered slower and/or more numerous) (to be measured, allow 1-2).
This note was finalized on 4th January 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: Roger Ahlman, Paul Coopmans, Ross Gallardy, Niels Krabbe, Frank Lambert, Mitch Leisinger, Huw Lloyd, Hans Matheve, John V Moore, Jonas Nilsson, Leonardo Ordoñez-Delgado, Fabrice Schmitt, Andrew Spencer and Charlie Vogt.
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: on362_black-capped_sparrow.pdf