In the following we briefly analyze and compare voice of the different races of Thick-billed Flowerpecker (Dicaeum agile). 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) and Macaulay Library (ML).
An overview of vocalizations per group (illustrated with multiple sonograms in the pdf version of this note):
Nominate group (agile/zeylonicum): Commonly heard voice is a sharp "spick". Also a fast series of higher-pitched notes (presumed song), a chattered series of more raspy short notes, and slightly longer high-pitched notes.
SE Asia group (pallescens, modestum, obsoletum a.o.): Vocalisations include chattered series of short raspy notes, and high-pitched notes, and seemingly also a fast series of higher-pitched notes (presumed song, very similar to previous group). Only the "spick" call of previous group apparently has not been recorded (yet).
Philippine group: We have found only 2 recordings, of the 'single, high-pitched note' type and possibly also a "spick" call (sonogram 2).
There are only a few recordings available of the SE Asia and Philippine group, and thus it is likely that vocal repertoire is more extensive than what can be deducted from the recordings. Nevertheless, it is quite clear that all groups share several vocalization types.
With the above evidence, we can only conclude that there is not a strong indication of vocal difference. At most, we can conclude that the sharp "spick" call (reaching c. 6kHz) has not been recorded in the SE Asian group, and furthermore there are some minor differences in note shapes. More recordings are needed to allow for a more in depth analysis.
The SE Asia group has been split from nominate Indian group, partly based on vocal differences (Rasmussen & Anderton 2012), but this is seemingly based on a single recording of SE Asia group, failing to document the entire vocabulary of this group.
This note was finalized on 23rd June 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 and ML: Patrik Åberg, Desmond Allen, Marc Anderson, Greg Budney, David Farrow, Vir Joshi, ben King, Albert Lastukhin, Petter Olsson, Rajgopal Patil, Craig Robson and Arnoud Van den Berg.
Rasmussen, P.C. & Anderton, J.C. (2012). Birds of South Asia: the Ripley Guide. Vols. 1–2. 2nd edition. National Museum of Natural History, Smithsonian Institution, Michigan State University & Lynx Edicions, Washington, D.C., Michigan & Barcelona.
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: on333_thick-billed_flowerpecker.pdf