Notes on the vocalizations of Black-and-white Triller (Lalage melanoleuca)

In the following we briefly analyze and compare the voice of the two races of Black-and-white Triller (Lalage melanoleuca). We also endeavour 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 online at Xeno Canto (XC), Macaulay Library (ML) and Avian Vocalization Center (AVoCet), and a larger set kindly provided by Rob Hutchinson, for a total of eight recordings of minor and 15 of melanoleuca.

Song of both taxa is a short phrase repeated several times (typically 3–12). After a pause, either this same song bout is repeated, or there is a switch to a slightly different one. The phrase typically consists of one or more short buzzy/scratchy notes followed by one or more whistles. In melanoleuca, there seems to be on average more buzzy/scratchy notes, with longer series as an introduction to an entire song bout, and the whistles are typically overslurred (rendered “weew”). In minor, there are usually only one or two buzzy/scratchy notes, and whistles are typically not overslurred (sharply rising or falling, or underslurred). Also, in melanoleuca, the song bout may possess two alternating, slightly different phrases, something not clearly identified in recordings of minor.

Differences are thus quite subtle or with overlapping characteristics, but nonetheless some are clearly quantifiable. The longest whistles in each phrase of melanoleuca are longer than in minor (range 0·17–0·45 seconds vs. 0·05–0·22 seconds). The whistles in each phrase of melanoleuca reach marginally lower frequencies than in minor (range 1500–1700 Hz vs. 1650–1950 Hz).

Calculation of Effect Size:

                           minor                                  melanoleuca                  Effect Size

Note length    Av. 0.16s SD 0.049s         Av. 0.276s SD 0.06s              2.11

Min. Freq.     Av. 1764Hz SD 109Hs     Av. 1573Hz SD 134Hz          1.56

When applying Tobias criteria, this leads to a total calculated vocal score of 2 + 1 = 3

This note was finalized on 7th January 2016, using sound recordings available online at that time. We would like to thank in particular the sound recordists: Desmond Allen, Rob Hutchinson, Robert Kennedy, Mike Nelson and Pam Rasmussen.

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: on181_black-and-white_triller.pdf