Notes on the vocalizations of Pale-legged Hornero (Furnarius leucopus)

In the following we briefly analyze and compare voice of the different races of Pale-legged Hornero (Furnarius leucopus). 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).

A potential split of this complex into 2 species has been discussed in http://www.museum.lsu.edu/~Remsen/SACCprop35.htm  From the discussion it is clear that while 'vocal differences' have been claimed in several field guides and elsewhere, few mention what these vocal differences are, let alone how different they are when quantified.

After having listened to recordings from all races, it seems to me that the loudsong is generally similar, a loud fairly long series of staccato notes which descend in pitch and decelerate at first and then stay at the same pitch and pace. There is thus not a race which stands apart by a 'very different song'. There is quite some variation within all races, probably depending on the level of excitement of the bird. Also, two birds often sing in asynchronous duet, and deliver somewhat different songs. Making abstraction of these variations, and choosing recordings of what looks like 'typical songs of birds which are not too excited', we found the following:

Caribbean Hornero group  (F. l. longirostris)

Measurements:

Note length in stable part of song:                0.085-0.1s

Max. freq. first notes                                     3450-3650Hz

Max. freq. notes in stable part                       2750-3000Hz

Pace of first notes (first 5 taken)                   0.43-0.58             

Pace of notes in stable part (5 notes)             0.75-1.08

Deceleration                                                   30-140%

Ratio note length/pause length                       0.7-0.9

Note shape                                                      Unique among all races, every note has at first a sharp peak and a downslurred part

Total length of song                                       5-8s

 

Pale-legged Hornero group - N of Amazon (F. l. leucopus)

Measurements:

Note length in stable part of song:                0.09-0.1s

Max. freq. first notes                                     3000-3900Hz

Max. freq. notes in stable part                       2500-3100Hz

Pace of first notes (first 5 taken)                   0.55-0.70             

Pace of notes in stable part (5 notes)            0.9-1.0

Deceleration                                                  30-70%

Ratio note length/pause length                      0.7-0.9

Note shape                                                     Every note has a completely flat top (only shared with cinnamomeus)

Total length of song                                       5-8s

 

Pale-legged Hornero group - S of Amazon  (F. l. tricolor , F. l. araguaiae, F. l. assimilis)

​Measurements:

Note length in stable part of song:                0.075-0.13s

Max. freq. first notes                                     2800-4000Hz

Max. freq. notes in stable part                       2300-2900Hz

Pace of first notes (first 5 taken)                   0.7-1.18

Pace of notes in stable part (5 notes)             0.9-1.36

Deceleration                                                   12-70%

Ratio note length/pause length                       0.5-1.0

Note shape                                                      Unique compared to other groups, every note has a burry top of several 'oscillations' and with an initial spike

Total length of song                                        4-6.7s

 

Pacific Hornero group  (F. l. cinnamomeus)

Measurements:

Note length in stable part of song:                 0.1-0.11s

Max. freq. first notes                                      3200-3300Hz

Max. freq. notes in stable part                        2700-2900Hz

Pace of first notes (first 5 taken)                    0.86-1.0

Pace of notes in stable part (5 notes)             1.0-1.2

Deceleration                                                   15-20%

Ratio note length/pause length                       0.65-0.75

Note shape                                                      Every note has a completely flat top (only shared with leucopus)

Total length of song                                        4-6s

 

From comparison of the above date, note shape seems to be the principal distinguishing feature, other basic parameters show certain differences but effect size is rather small. Note shape can be quantified by e.g. defining parameters like 'frequency range between 0.2-0.8 of note length', 'number of changes in slope from rising to falling per note' etc. and would lead to ranges not overlapping between 3 groups, although obviously it is debatable whether scoring into such detail is applicable.

 

Conclusion:

It would thus seem that vocal differences are less striking than typically assumed.

Caribbean Hornero versus all others: Unique among all races, every note has at first a sharp peak followed by a downslurred part (score 3, at most!), and song has largest deceleration with first notes shortest in length (score 1). This would lead to a total vocal score of at most 4 when applying Tobias criteria.

Pale-legged Hornero south of Amazon versus all others: Unique compared to other groups, every note has a burry top of several 'oscillations' and with an initial spike (score 3, at most!)

Pacific Hornero versus Caribbean and Pale-legged Hornero S of Amazon: Note shape has a flat top (score 3, at most!) and song has by far smallest deceleration (score 1-2). This would lead to a total score of about 4.

Pacific Hornero vs. Pale-legged Hornero N of Amazon: Song has smallest deceleration (score 2, more than previous as ranges are more divergent)

 

This note was finalized on 10th April 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: on88_pale-legged_hornero.pdf