ajohn

Today during the bird race our team discovered a Yellow-streaked Warbler near Ping Che in the northern NT.
We had initially identified the bird as possibly Radde's Warbler, but fortunately the bird was singing and when we checked the songs on xeno-canto later we were able to confirm ID as Yellow-streaked. The song was a series of fairly short, accelerating notes followed by a short trill; this can be heard at http://www.xeno-canto.org/asia/b ... ler&species_nr=

Directions (unfortunately the location is not easy to describe!):
The bird was along the road connecting Ping Yeung village to Wo Keng Shan Road.
From Wo Keng Shan Road (just before the NENT landfill) follow the road through some plantation woodland. After the track comes out of the woodland, it bends around the base of the small hill. Before you reach the burnt area, on the left is a single house. The bird was alongside the track, initially just above the track but it later flew down towards the house. It was perching mostly in low trees and singing frequently.

ajohn

It was initially very close but slightly silhouetted against the sky, and I thought that the structure was closer to Dusky - the bill was not as heavy or the legs as thick as I would expect of Radde's. This was one reason my mind had started to consider Yellow-streaked.
It then flew overhead and downhill to a point where it was not against the sky and disappeared for a couple of minutes. When it hopped out again, I thought it looked very similar to Radde's in terms of plumage but the view was so short that I didn't manage to get much by way of detail.

ajohn

There is a summary of the features Paul Leader thinks are useful on this thread: http://www.hkbws.org.hk/BBS/viewthread.php?tid=9047. There are some pictures on OBI: http://orientalbirdimages.org/search.php?Bird_ID=1830

Given that Dusky Warbler is the 'default' species of this group in HK, I think that familiarity with that species is very important, including familiarity with the range of variation. The Ping Che bird struck me as being similar in structure to Dusky but with a head pattern unlike that I have ever seen on Dusky, and more similar to Radde's (particularly the long supercilium, white behing the eye).

I wonder if habitat may be a useful indicator as well. The Ping che bird was in low shrub on the edge of a dry hillslope. I have seen Yellow-streaked in similar habitat in China. Dusky will use this habitat in HK (and was present in the same area at Ping Che) but in  my experience Radde's tends to be found in more mature wooded areas.

But as Mike mentioned voice is really the key. I was fortunate that the Ping Che bird was singing. It was this song which initially drew my attention and which finally led to clinching the ID. Again, familiarity with the song of Dusky (there are many singing at the moment) is useful in this respect. Knowing the calls of the species would also be crucial to picking out Yellow-streaked at other times.

ajohn

The Ping Che bird was singing continuously on the day it was found, when it was not affected by the use of tapes. I don't know the extent to which tapes were used in subsequent days, but it is possible this did not increase the frequency of singing. However, the bird wasn't certainly heard to call during the period of observation.

I had actually assumed that, rather than being a passage bird, this could be an individual which has overwintered undetected in this location (where there are few birdwatchers), and that it had started to sing as spring arrived, in the same way as Dusky Warblers. It's not so unusual for some Phylloscopus to sing while in HK despite being distant from breeding grounds (Dusky, Yellow-browed, Pallas's and Arctic/Japanese all sing relatively regularly).