In the following we briefly analyze and compare voice of the different races of Barred Antshrike (Thamnophilus doliatus). 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).
When listening to the loudsong of the many subspecies of Barred Antshrike, it becomes quickly apparent that there are some vocal differences between races north and south of the Amazon river. Furthermore, the caatinga race capistratus was proposed as a separate species (Assis et al. 2007), for which we will consider this as a third group in our comparison.
We have taken a random sample of 10 songs for each of the following 3 groups: capistratus, races north of the Amazon and races S of the Amazon (excl. capistratus). We measured several basic sound parameters, and given that differences may be rather small, we have calculated for all average, standard deviation and effect size in order to reach calculated scores.
data range Av SD
total length 2.09-3.0 2.56 0.32
# notes 14-20 17.9 2.13
max pace* 0.094-0.115 0.101 0.008
length last note 0.11-0.21 0.158 0.034
max. freq. start 750-1120 937 171
max. freq. middle 720-930 852 56
max. freq end 640-780 730 40
max. freq last note 620-790 745 51
delta end vs last note -20 to 55 15 26
N of Amazon
data range Av SD
total length 2.48-3.6 2.94 0.39
# notes 20-30 25.9 4.4
max pace 0.07-0.1 0.088 0.011
length last note 0.11-0.165 0.135 0.017
max. freq. start 700-940 836 75
max. freq. middle 870-1000 945 46
max. freq end 750-920 860 56
max. freq last note 800-1040 940 85
delta end vs last note 30-180 80 48
S of Amazon
data range Av SD
total length 1.9-2.76 2.24 0.29
# notes 12-20 14.9 2.4
max pace 0.08-0.16 0.12 0.021
length last note 0.105-0.20 0.137 0.027
max. freq. start 1000-1340 1102 103
max. freq. middle 960-1200 1112 132
max. freq end 718-900 786 69
max. freq last note 730-990 877 90
delta end vs last note 25-210 89 57
* pace is here measured by the period, duration between 2 subsequent notes
capistratus capistratus North vs South
vs North vs South
total length 1.065 1.048 2.037
# notes 2.31 1.32 3.1
max pace 1.35 1.20 1.91
length last note 0.86 0.68 0.089
max. freq. start 0.76 1.17 2.95
max. freq. middle 1.81 2.56 1.69
max. freq end 2.67 0.99 1.18
max. freq last note 2.78 1.8 0.72
delta end vs last note 1.68 1.67 0.17
Assis et al. (2009) state that capistratus has 'more elements' and 'longer final element' . The former could be confirmed, although with considerable overlap. Length of final note seems to be rather similar in the samples checked.
At the other hand, in comparison with other races south of the Amazon, capistratus seems to reach a higher pace. Also, there is more a tendency for the song going up and down in pitch, rather than going down in pitch in other races, possibly linked with a slightly different note shape. Differences are however not large at all, and may well blur further when a larger set of recordings is investigated, for all races south of the Amazon.
From the above, we can conclude that there is no parameter where capistratus differs from birds N and S of Amazon with an effect size larger than 2 (needed to reach a score of 2).
There are however differences that reach a score of 1: capistratus has a last note which is on average lower in frequency, and which does not rise a lot versus the previous note. Also in the middle and end of the note series, the max. frequency is lower. Other differences are in between N and S birds, and would thus be even less outspoken if these 2 groups were to be merged. Total score for capistratus vs. all others is thus 1 or 2.
N and S birds differ mainly in number of notes (score 2), total length (2), etc. and would thus reach a total score of 4 (when capistratus is not included in S birds) or about 3 (when capistratus is included in S birds). One could argue that with more recordings for N and S groups, differences may get less distinct. However, the recordings were taken randomly from a wide range, and we did not distinguish between male/female song or whether playback was used or not, which typically increases the variability. All in all, this score is thus quite representative we believe, and reflects a clear but moderate difference in loudsong between birds north and south of the Amazon river.
This note was finalized on 31st 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.
Assis, C.P., Raposo, M.A., Stopiglia, R. and Parrini, R. (2007). Validation of Thamnophilus capistratus Lesson, 1840 (Passeriformes: Thamnophilidae). Auk 124(2): 665-676.
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: on53_barred_antshrike.pdf