Arctic Warblers from Hong Kong

Details of specific status and identification of forms xanthodryas, borealis and examinandus can be found here:

Alström et al 2011: The Arctic Warbler Phylloscopus borealis – three anciently separated cryptic species revealed, Ibis (2011), 153, 395–410

Songs and calls be found here:

Per Alström's web page

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!).


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.

1. 29. April 2012 Po Toi

All syllables are of the same type. Therefore this should be a borealis.

2. 6 May 2012 Po Toi

A very poor recording, but again all the syllables are similar.

3. 6 May 2012 Po Toi

Again a poor recording, but all the syllables seem to be similar.

4.7 May 2012 Tin Shui Wai

This song sounds a little pulsating, and some of the notes are slightly different, but still this should be a borealis.

5. 7 May 2012 Tin Shui Wai

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.


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).

1. 6 May 2012 Po Toi (1058)

A fast call with most energy centered around 6000 Hz is clearly a borealis call.

2. 6 May 2012 Po Toi (1059)

Again, a borealis.

3. 6 May 2012 Po Toi (1063)

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.