In the following we briefly analyze and compare voice of the different races of Mexican Jay (Aphelocoma ultramarina). 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).
Vocabulary of the Mexican Jay is quite limited, the most common vocalization being an upslurred grating call note, repeated singly, doubled or in series. As comparison of voice between the different races basically boils down to putting this call note 'under the microscope', I have taken randomly some 5 recordings of the 3 groups: EAST group (couchii), WEST group (arizonae, wollweberi, (gracilis=no recordings)) and SOUTH group (colimae, ultramarinae)(illustrated with multiple sonograms in the pdf version of this note).
Call notes are remarkably constant within each group. Surprisingly, the eastern group is the most diagnostic, having shorter notes with steeper increase in pitch and lowest two frequency bands are close and 'smudged together'. Differences between WEST and SOUTH are much more subtle, the latter seems to start every note typically grating and ends rather less so.
longest note gap between lowest min. freq.
2 freq. bands
EAST 0.11 - 0.15s 600 - 1000 Hz 900 - 1100Hz
WEST 0.14 - 0.18s 900 - 1100 Hz 1400 - 1800 Hz
SOUTH 0.17 - 0.20s 1000 - 1200 Hz 1200 - 1500 Hz
Which would lead to following scores for vocal difference:
EAST vs. SOUTH: 2 for note length and 2 for min freq. -> total score 4
WEST vs. SOUTH: 1 for note length and 1 for min. freq. and freq. band pattern -> total score 2
EAST vs. WEST: 2 for note length and 2 for min. freq. -> total score 4
Vocally, EAST group is thus the most distinctive. WEST and SOUTH groups only differ in minor details. (We should also note that the frequency measurements are less precise than length measurements here, due to 'smudging' on the sonogram).
We have finally also analyzed two recordings of the so-called CENTRAL group (potosina): the call notes look less 'smudged' than couchii, but measurements are closest to EAST group:
longest note gap lowest min. freq.
2 freq. bands
CENTRAL 0.10 - 0.12s 700 - 900Hz 1100 - 1150Hz
Thus, if we merge EAST group and CENTRAL group, this hardly changes the picture of vocal differences , as explained above.
In conclusion, the EAST/CENTRAL group (couchii and potosina) shows the highest vocal differentiation, while WEST group (arizonae, wollweberi, (gracilis=no recordings)) and SOUTH group (colimae, ultramarinae) show minor vocal differences. Other vocalizations may add information to this conclusion, but at present there are hardly any recordings of these.
This note was finalized on 3rd March 2016, 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.
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: on211_mexican_jay.pdf