Wednesday, 31 October 2012

Mystery acro

I decided to do a quick check of Knockadoon Head this evening after the showers had cleared. Plenty of Blackbirds, Song Thrushes and Robins about with a single Chiffchaff in the willows near the campsite.
I drove on to the Holy Ground lane and just as I got out of my car I came across this Acro feeding busily in the willows by the galvanised iron gate. It was difficult to get any detail on the bird as it moved around in fairly thick cover. However on the basis of the few shots I got in fading light I was quite happy that the bird is a juvenile Reed Warbler. The main reasons for thinking this were the long primary projection, the buffy rump, undertail coverts and flanks and it lacked the short bill that I'd expect for Blyth's Reed.

I emailed the above two shots to Owen Foley and he concurred that it lacked features for Blyth's but that I should check the emargination line for Reed and Marsh.
This is where I got confused. According to some of the on-line details I checked, the emargination on P2 for Reed should be in line with the tips of the secondaries and below the tips of the secondaries for Marsh. I cropped the above two shots to see where the emargination is and to me it would appear to be below the tips of the secondaries.

Not easy to tell in this photo but the P2 emargination would appear to sit below the secondary tips

Emargination on P2 seems below the line of the secondaries
And several other things occurred to me as I worked on these shots. The tips of the primaries are buff / off-white as in Marsh and the feet are yellow - as in Marsh.
So I have several questions;

Can juvenile Marsh Warblers appear buffy?
Is Marsh likely this late in the autumn?
Is the bill right for Marsh - looks a little large to me.

Two final points I might add, firstly the posture looked more 'Reedy' to me. Secondly, the bird was pretty quiet but did give the odd soft tick or tchek but then again I think most unstreaked Acro's do that anyway.

Comments and thoughts welcomed!


  1. Hi Graham, I seem to remember Killian telling me that if the longest tertial stretched beyond the secondaries - forming a step - then it's a Marsh Warbler. HOWEVER!! I could be remembering that completely the wrong way around!! If not, this bird looks like it's a Marsh Warbler....

  2. Hi all,
    To me, the following features make this a Reed Warbler:
    -the emargination on the third primary falls well back on the wing, more of less level with the tip of the innermost primary or even the secondary tips. This is much better for Reed than Marsh, on which the same emargination often falls level with the tip of the seventh primary, more or less.

    -the facial pattern, with the broken eyering being far and away the most obvious feature, is typical for Reed. Marsh often have a pale supraloral area...though this is not as blindingly obvious as on a classic Blyth's Reed, it certainly does give identifiable individuals a different appearance.

    -the bill seems too thin for Marsh.

    -I'd like a Marsh Warbler to have a slightly longer primary projection than this, but, of course, there is some overlap.

    -I'd also expect an identifiable Marsh Warbler to perhaps show a greater contrast between dark tertial centres and well-defined pale fringes than this bird shows.

    Also, the calls. To my ears, Reed's tacking call is reminiscent of that of a Eurasian Stonechat, with a definite 'ch' sound, 'chak', whereas Marsh (like Blyth's Reed) give a more Blackcap/Lesser Whitethroat-like 'tak'. Subtle, but they do sound different.