Tuesday, October 14, 2014

Sakhalin Leaf Warbler?

I took an early morning walk around the Ministry of Public Relations today.

Migrants were in evidence with two Brown Shrikes,  a couple of Black-naped Orioles, and a calling Ashy Minivet, whilst one small area of trees held an Asian Brown Flycatcher and three Phylloscs: one Eastern Crowned Warbler, one Yellow-browed Warbler and one Pale-legged/Sakhalin Leaf Warbler.

The PLLW/Sakhalin obviously held my interest - the conundrum of how to separate these birds in the field is one that is still very poorly understood, with the only birds confirmed as Sakhalin having been spring passage migrants in song. Current indications of the numbers of Sakhalins passing through Thailand on migration are based upon mist-netted long-winged male birds who's biometrics put them outside the range of PLLW.  Phil Round has also commented to me that "It's not that clear-cut, but generally PLLW looks to have a pale, or only slightly sullied lower mandible", so it may well be that this is another feature that can be used to support in-the-field ID.

Regarding this morning's bird, it was foraging in the mid-storey of a tree, about 6 metres off the ground, but then responded strong to pishing by dropping lower and giving views at close range (sadly I didn't have the camera with me).  I played the contact call of Sakhalin LW (a wintering bird confirmed in Sinagpore last winter) and my bird responded immediately with an identical call. By contrast it did not respond at all when I played a PLLW call a couple of minutes later.  Although the views were close it was difficult to judge the colour of the lower mandible, and the upperparts (and thus primary projection) could not be seen.

Given the immediate response to playback, should I tick this bird as a Sakhalin? It doesn't seem unreasonable.  Sakhalin LW is evidently not uncommon as a passage migrant, and in fact Phil suggests that, based on his ringing data during spring passage "the numbers of Sakhalin LW swamp those of PLLW in the Bangkok area".

What I'm aiming to do is really examine each PLLW/Sakhalin that I encounter, to see if there are other features or behavioral traits that can be used to help identify these two species in the field, but this remains a tough challenge.

1 comment:

Mark James Pearson said...

Following your PL/S encounters with interest Dave....