Notes on the vocalizations of Olive-brown Oriole (Oriolus melanotis)

In the following we briefly analyze and compare voice of the two races of Olive-brown Oriole (Oriolus melanotis). 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).

We have located recordings of race finschi from Wetar, and of race melanotis from both Timor and Roti. We have measured a number of basic sound parameters and calculated effect sizes:

finschi (n=10): Song often consists of a single loud whistle, which often rises in pitch before dropping. Sometimes whistle is preceded by one or (rarely) a few very short notes.

                                                    range                            Average            Standard Dev.

min.freq.                                    580 - 1600Hz                   889Hz                298Hz

max. freq.                                   2300 - 3150Hz                 2821Hz             277Hz

freq. range                                 1430 - 2500Hz                 1930Hz              340Hz

min. phrase length                       0.32 - 0.75s                      0.50s                 0.14s

max. phrase length                       0.35 - 0.86s                      0.61s                 0.25s

shortest note length                     0.025 - 0.46s                    0.24s                  0.19s

longest note length                       0.35 - 0.50s                      0.44s                 0.07s

# notes/phrase                                1 - 3                                  1.7                    0.85

 

melanotis(n=10): Song typically consists of one or a few short notes followed by a slightly longer loud whistle, which typically drops abruptly in pitch about halfway (thus sounding bisyllabic).

                                                   range                          Average                Standard Dev.

min.freq.                                    520 - 960Hz                717Hz                    139Hz

max. freq.                                 1520 - 2500Hz            1906Hz                  308Hz

freq. range                                 850 - 1870Hz             1190Hz                  289Hz

min. phrase length                      0.52 - 0.98s                  0.77s                      0.14s

max. phrase length                     0.55 - 1.00s                   0.80s                      0.15s

shortest note length                    0.03 - 0.18s                    0.10s                    0.04s

longest note length                     0.24 - 0.54s                    0.40s                    0.09s

# notes/phrase                              2 - 5                               3.0                       0.9

 

Main differences in basic parameters are:

                                                          effect size                             score

max. freq.                                           3.12                                       2

freq. range                                         2.35                                       2

min. phrase length                             1.93                                       1

shortest note length                          1.02                                       1

#notes/phrase                                    1.49                                       1

 

Unlike finschi, song phrase of melanotis apparently never consists of a single long whistle, whistles don't reach as high frequencies as finschi and lack the rather typical (irregular) overslurred shape of finschi , resulting in a smaller frequency range. When applying Tobias criteria, this would lead to a total score of 3-4 (depending whether we consider max. freq. and freq. range independent or not).

 

This note was finalized on 9th October 2015, 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: Timothy Burr, Stijn Coleman, Hervé Jacob, Frank Lambert, Mike Nelson, Colin Trainor and Philippe Verbelen.

 

References

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: on160_olive-brown_oriole.pdf