Notes on the vocalizations of Slaty-capped Shrike-vireo (Vireolanius leucotis)

In the following we briefly analyze and compare voice of the different races of Slaty-capped Shrike-vireo (Vireolanius leucotis). 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).

Song of all races is structurally the same: a single loud melodious whistle endlessly repeated. This whistle is however slightly different among races:

V. l. mikettae (W Colombia (S of R San Juan) and W Ecuador (S to NW Azuay))

n=8                                                 range                            average                 SD

start freq.                                    2700 - 3100Hz               2876Hz                  176Hz

end freq.                                     1760 - 2300Hz               2141Hz                  163Hz

freq. drop in main part                  0 - 120Hz                        54Hz                   40Hz

length                                             0.66 - 0.84s                    0.75s                   0.06s

V. l. leucotis (S Venezuela (Bolívar, Amazonas) and the Guianas S to N Brazil (N of Amazon); extreme S Colombia (SE Nariño), E Ecuador and N Peru (S to San Martín)).

n=15                                              range                            average                 SD

start freq.                                   2500 - 2920Hz                2705Hz                  152Hz   

end freq.                                    1750 - 2000Hz                 1892Hz                 65Hz                     

freq. drop in main part               200 - 470Hz                    360Hz                   84Hz

length                                           0.48 - 0.65s                     0.55s                    0.06s

V. l. simplex (E Peru (Huánuco S to Ayacucho and Cuzco) and NC Brazil S of Amazon (R Purús E to R Tocantins, S to NW Mato Grosso)) and V. l. bolivianus (SE Peru (Cuzco) S to NC Bolivia (La Paz, Cochabamba and Santa Cruz)).

n=12                                              range                            average                 SD

start freq.                                   2500 - 3000Hz               2718Hz                  172Hz

end freq.                                    1530 - 1950Hz               1693Hz                  118Hz

freq. drop in main part                350 - 700Hz                  560Hz                    145hz    

length                                            0.42 - 0.86s                   0.60s                    0.12s

 

Effect size calculation:

                           mikettae vs. leucotis    mikettae vs. simplex     leucotis vs simplex

end freq.                           2.0                               3.15                               2.07

freq. drop                         4.65                              4.76                               1.69

length                              3.33                               1.58                               0.53

 

When applying Tobias criteria, this translates in the following vocal scores:

                                       mikettae vs. leucotis    mikettae vs. simplex    leucotis vs simplex

end freq.                                     2 (just)                          2                               2 (just)

freq. drop                                    2                                  2                                1

length                                         2                                  1                                 1

TOTAL VOCAL SCORE          4                                 4                                 3 (just)

mikettae has a whistle which hardly drops in pitch (between about 10% and 90% of its length), as a consequence reaches not that low frequencies. Whistle is also longer in length. -> total score of 4 vs both other races

leucotis is closer to simplex/bolivianus, but its whistle drops less in frequency, and as a consequence doesn't reach that low frequencies, although there is some overlap. -> total score 3 at most (may be reduced to 2 with larger set of recordings)

 

This note was finalized on 19th October 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: on167_slaty-capped_shrike-vireo.pdf