In the following we briefly analyze and compare voice of the different races of Olivaceous Flatbill (Rhynchocyclus olivaceus). 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).
There seem to be 2 groups which have a very different song:
Group 1: birds from Panama south to Bolivia and E to NE Venezuela (races bardus, mirus, flavus, aequinoctialis and jelambianus): Song is a series of typically 5-10 whistles, initially flat and burry, gradually shifting to louder purer whistles which accelerate and rise in pitch (sometimes ending in a stuttered series, possibly when excited or after playback).
We measured following parameters (n=12):
# of notes 5-10 (up to 18 in excited songs)
total length 1.72-3.0s
longest note 0.31-0.47s (down to 0.20s in excited songs)
start mid freq. 1940-3000Hz
end mid. freq. 2900-3600Hz
start minus end freq -550Hz to -1100Hz
total freq range 1700-3000Hz (less in poor recordings not capturing all frequencies)
average pace 0.31-0.46s (down to 0.14s in excited songs)
Group 2: birds from the Guianas and S of the Amazon east of the river Madeira (races guianensis, sordidus and olivaceus): Song is a fast series of very buzzy notes (covering a wide freq. range with many close frequency bands), which descend in pitch. There is no clear acceleration/deceleration.
# of notes 8-20
total length 0.85-2.9s
longest note 0.075-0.13s (up to 0.26s when excited, with emphasized initial notes)
start mid freq. 3500-4500Hz
end mid. freq. 2100-2900Hz
start minus end freq +600Hz to +1900Hz
total freq range 2100-3000Hz
average pace 0.08-0.11s (up to 0.145s when excited, with emphasized initial notes)
Comparison of the 2 groups: The rising vs. descending series is reflected in the parameter 'start freq. minus end. freq.' (score 3-4), also average pace is much faster in eastern birds (score 2-3), while song of the latter group is further typified by a higher start frequency and a lower end frequency (score 2-3), shorter notes (score 2-3). When applying Tobias criteria this would result in a total score for vocal difference of about 6.
Some caution is needed however: There is a single recording (XC90673) from W Amazonia (the only recording in a radius of c. 800km), which has a somewhat intermediate voice, lacking the typical parameters of any group. This may be an indication of a clinal zone in W Amazonia south of the Amazon river.
More vocal differences may be found in call notes, as Group 1 frequently utters a short explosive harsh rising rattle while this is not the case in Group 2.
This note was finalized on 18th August 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: Peter Boesman, Paul Coopmans, Fernando de Godoy, Rodrigo Dela Rosa, Dan Lane, Alex Lees, Niels Krabbe, Gabriel Leite, Curtis Marantz, Oscar Marin, Sjoerd Mayer, Jeremy Minns, Mark Robbins, Paul Schwartz, Andrew Spencer and Herman Van Oosten.
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: on120_olivaceous_flatbill.pdf