I was walking down South Valley about 10ish this morning when a Blackcap flew up followed by a second bird that I thought was going to be a Garden Warbler, but it was an acro!
I watched it off & on, more off than on, for an hour or so & got quite a few not massively helpful photos & was leaning towards it being a Marsh Warbler.
Looking at the photos on the computer & doing some reading up I'm still not 100% sure, partly because its been suggested any very late acro isn't going to be a Marsh Warbler and partly because I'm not sure if the photos undisputably show the wing formula.
The vast majority of Marsh Warblers have the 2nd primary longer than the 4th - in the photos of this bird primary 2 looks about the same, possibly longer in one photo, possibly shorter in another depending on the angle - there is one photo of the closed wing slightly from underneath that possibly shows the 2nd primary clearly longer than the 4th, if the dark mark is the tip of the 2nd primary! So not sure on that.
If you draw a line across from where the emargination ends on the 3rd primary of a Marsh Warbler it should line up with tip of about the 7th primary, on Reed Warbler it should fall level with about the 10th primary - all the photos seem to show it being about the 7th or 8th primary depending on what angle you draw the line at. Bit happier about this feature.
Bill looks stout in most of the photos, more pointy in a couple - leaning towards Marsh on this. Obvious pale tips to the primaries? - apparently not a brilliant feature in the autumn, this bird has got pale tips but I'm not convinced anything above and beyond a Reed Warbler. The claws look very pro-Marsh to me, fairly plain, lacking obvious contrast between the dark upperside and yellowish underside.
I've seen quite a few 'interesting' looking autumn acros on the east coast that just looked and sounded like Reed Warblers to me but this bird never looked like a Reed Warbler & it was making a low 'chuck' call which isn't a call I would associate with a Reed Warbler.
I've got to do some work now but I'll hopefully be able to make the time to go and have another look - a Yellow Wagtail flew over calling while I was watching the acro.
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