Notes on the vocalizations of Rough-legged Tyrannulet (Phyllomyias burmeisteri)

In the following we briefly analyze and compare voice of the different races of Rough-legged Tyrannulet (Phyllomyias burmeisteri). 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).

Typical vocalization is a repeated single overslurred note "pseet". Less often, a faster series of similar notes is given (often slightly descending). While structurally about identical, there are clearly 2 vocal groups based on basic sound parameters:

Group 1: All races north of the Peruvian/Bolivian border (n=9)

Measurements:

Note length                          0.22-0.37s (race zeledoni seemingly longest notes)

min. freq.                              4100-5200Hz

max. freq.                             6400-7100Hz

pace*                                    0.33-0.40s (for fast series)

Group 2: South and east of Peruvian/Bolivian border (burmeisteri) (n=9)

Measurements:

Note length                          0.14-0.24s

min. freq.                              3100-3500Hz

max. freq.                             4900-5700Hz

pace                                      0.25-0.33s (for fast series)

* pace measured here as period, duration between two consecutive notes

Note: recording XC4080 of La Paz, Bolivia seems to fit rather Group 1, and may be an indication that this group extends somewhat further south (or alternatively that there is a hybrid zone where both groups meet, see also http://www.xeno-canto.org/forum/topic/12389)

Group 2 differs from Group 1 in having lower-pitched notes (score 3) which are slightly shorter (score 1-2). Fast note series tend to be delivered at a slightly higher pace (and seem to have slightly more notes) (score 1-2). When applying Tobias criteria this would lead to a total vocal score of about 4.

This note was finalized on 19th August 2015, using sound recordings available on-line at that moment. We would like to thank in particular the many sound recordists who placed their recordings for this species on XC.

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: on137_rough-legged_tyrannulet.pdf