Julien Meyer has done extensive work in covering the anthropology of whistling languages as well as other non-spoken languages. In his academic paper mentioned in the title, I found an account where he delves into the linguistic nature of Silbo documenting it’s phonetic structure in order to compare it with other whistling languages he has researched. He alludes to the fact that Silbo is a highly developed language in comparison to the simplistic herder/farmer based whistling language’s purpose to communicate basic messages over long distance. We see this as Meyer mentions how the language employs vowels and their distinct tonal properties, displaying the ability to articulate well informed messages. “The spoken vowels /i, e, a, o, u/ are therefore whistled in five bands, some of which overlap strongly.” … “Four intervals are statistically different (/i/, /e/, /a/ and /o, u/) in a decreasing order of mean frequencies”.

 The graph displays certain frequency bands that whistlers recognise as pitches correlating to Spanish vowels. This hints the language to be a proxy language, adapted for telephonic purposes rather than a primordial whistling language. There is no mention however in this paper the phonetic production of consonants in Silbo.