Notes on the vocalizations of Plain Xenops (Xenops minutus)

In the following we briefly analyze and compare voice of the different races of Plain Xenops (Xenops minutus). 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).

Based on a screening of all available recordings over the entire range, it would seem that there are clearly 3 vocal groups:

NW group (from Mexico to NW Ecuador, N Colombia and NW Venezuela)

Song is a fast series of high pitched notes, which typically starts with a few spaced notes. Within this group, northern birds south to about C Panama (mexicanus, ridgwayi) can be distinguished from birds further south (littoralis, olivaceus, neglectus): the former have a song that accelerates and goes up and down in pitch, the latter have a song rising in pitch with less acceleration and fewer notes.

Measurements:

                                              northern subgroup (n=7)         southern subgroup (n=10)

# of notes                              18-20                                       8-15

max. pace                              0.05-0.065s                             0.09-0.14s           

max. freq.                              6800-7600Hz                          6630-8100Hz

min top freq.                         3800-6200Hz                          3800-7000Hz

min. freq.                               2500-3300Hz                         2400-3800Hz

min. note length                     0.035-0.04s                            0.05-0.055s

max. note length                    0.055-0.07s                            0.052-0.058s

 

 

Amazonian/Guianan group with extreme NE Brazil (S and E Venezuela, Guianas, E Colombia, E Ecuador, E Peru, Amazonian Brazil and extreme NE Brazil)

Song over most of its range (remoratus, ruficaudus, obsoletus) is a simple series of about 5-7 high-pitched overslurred notes delivered at a steady pace, and (usually) going up and down in pitch. In SE Amazonia (genibarbis) there seems to be a tendency to start with some faster notes (not always). In extreme cases, there is some resemblance with the southern subgroup of 'NW group'. This is apparently not seen in alagoanus, where typical song is delivered.

Measurements:

                                               most of region (n=14)           SE subgroup (n=6)

# of notes                               3-9                                         3-10

max. pace                               0.16-0.25s                             0.10-0.17s           

max. freq.                               6100-8000                            6100-7000Hz

min top freq.                          4300-7100Hz                        5600-5800Hz

min. freq.                                1800-2600Hz                       1900-2300Hz

min. note length                      0.06-0.08s                            0.065-0.08s

max. note length                     0.06-0.09s                            0.085-0.09s

 

S Atlantic group (from Bahia, Brazil to Argentina)(minutus)

Song over its entire range is a series of about 4-5 upslurred notes, the first one slightly lower-pitched and subdued.

Measurements:

                                                most of region (n=14)                                                      

# of notes                                2-6                                                                       

max. pace                               0.26-0.35s                                                                          

max. freq.                               6400-7600Hz                                                                     

min top freq.                           5300-6200Hz                                                                     

min. freq.                                3100-3700Hz                                                                     

min. note length                      0.12-0.18s                                                                          

max. note length                     0.15-0.23s           

           

Differences among the 3 vocal groups are thus quite clear:

 

S Atlantic group ( minutus) is unique in having longer upslurred notes (note length: score 3-4) and the slowest pace (score 2). It differs further from the NW group in having less notes, and from the Amazon/Guianan group in not reaching that low frequencies (score 1-2). This would lead to a total vocal score of 5-6 applying Tobias criteria.

The two remaining groups are also quite distinct, although the level of variation masks somewhat the obvious differences between typical songs. Nevertheless, the NW group has the highest number of notes (score 1-2), the fastest pace (score 1-2), higher low frequencies (score 1-2), and the shortest notes (score 2). This would lead to a total vocal score of about 4.

Furthermore, within the last two groups, two subgroups can be distinguished, having minor vocal differences.

        

This note was finalized on 28th 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 and ML.

 

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: on85_plain_xenops.pdf