In the following we briefly analyze and compare voice of the different races of Northern Golden Bulbul (Thapsinillas longirostris). 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 Avian Vocalizations Center (AVoCet).
Collar et al. (2013) proposed to split present complex into five species: Sangihe Golden Bulbul (Thapsinillas platenae), Togian Golden Bulbul (Thapsinillas aurea), Halmahera Golden Bulbul (Thapsinillas chloris) and Obi Golden Bulbul (Thapsinillas lucasi), but retained race harterti in Sula Golden Bulbul (Thapsinillas longirostris).
In recent years, more voice recordings have become available of harterti and longirostris, for which we will focus here on these two taxa. Some examples of voice (illustrated with sonograms in the pdf version of this note):
* A series of croaking notes followed by more musical whistles (typically two notes alternating), presumably the song.
* a complex jumbling, possibly of several birds, of guttural and more melodious notes, presumably interaction calls.
* a high-pitched nasal drawn-out call
* A short whistled phrase with rather abrupt start and end, somewhat oriole-like. Sometimes initiated with some more scratchy notes.
Vocalizations thus seem to be very different. Differences can be quantified as follows: harterti differs from longirostris by much shorter song phrase (3) which lacks alternating note series (2), and a seemingly different vocabulary of call notes. Application of Tobias criteria would lead to a total vocal score of about 5 (based on these few recordings, assuming these are representative!).
This note was finalized on 12th July 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 AVoCet: Frank Lambert, Filip Verbelen and Peter Wilton.
Collar, N.J., Eaton, J.A. & Hutchinson, R.O. (2013). Species limits in the Golden Bulbul Alophoixus (Thapsinillas) affinis complex. Forktail 29: 19–24.
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: on426_northern_golden_bulbul.pdf