Arctic Warblers from Hong Kong
Details of specific status and identification of forms xanthodryas, borealis and examinandus can be found here:
Songs and calls be found here:
Both borealis and xanthodryas have been recorded in Hong Kong. The former mostly in autumn and the latter mostly in spring.
The following recordings were recorded in Hong Kong in spring of 2012. The quality of the recordings is mostly quite poor for a variety of reasons (noisy background, quiet songs, even the condition of the recording equipment was not at its best at the end of the long trip!).
Songs
Many Arctic Warblers did sing in Hong Kong. However, many of the songs seem to be not fully crystallized. In short, borealis song is fast with similar syllables throughout. Examinandus and xanthodryas songs have a pulsating rhythm with alternating syllables.
All syllables are of the same type. Therefore this should be a borealis.
A very poor recording, but again all the syllables are similar.
Again a poor recording, but all the syllables seem to be similar.
This song sounds a little pulsating, and some of the notes are slightly different, but still this should be a borealis.
This was thought to be a different individual from the previous one, although it was quite close and the song was similar, ie most probably borealis.
Calls
In short, the borealis call is high-pitched and very fast, examinandus slower (and therefore clearly rattling) and xanthodryas fast but lower-pitched (see the above mentioned references).
A fast call with most energy centered around 6000 Hz is clearly a borealis call.
Again, a borealis.
Again, a borealis.
4. 7 May 2012 Tin Shui Wai (1066)
Again, a borealis.
So, all individuals we identified in Hong Kong in late April and early May 2012 were borealis. This is somewhat surprising because xanthodryas is thought to occur in Hong Kong in spring.