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The 'Kelynack' Warbler - some comments by Brian Small

(pictures by Pete Wragg - submitted to GB Scarce Birds Gallery)

During October an Acrocephalus warbler was found at Kelynack, Cornwall. Pete Wragg managed to get these instructive shots of the bird on the 14th October. Initially thought by some observers to be a Marsh Warbler (Acrocephalus palustris), others tentatively suggested the eastern race of Reed Warbler known as Caspian Reed Warbler (accorded full species status by some - Acrocephalus fuscus). Brian Small now offers some thoughts.


"I have looked carefully at a number of the images, though it is hard to get much of the colour as described by Julian Hough (*1). There may be structural features of the wing to help, and I lay out my feelings here more as a catalyst for discussion rather than fact.

I believe that this is not a Marsh Warbler. The overall impression is wrong. The underparts colour (hard to tell) should be washed ochre or yellowish and the upperparts should have a greenish tone if this was a Marsh Warbler. The wing length of Marsh Warbler averages only one mm longer than fuscus so that won't help.

Reed Warbler

The length of p2 is interesting and on the 'Kelynack' bird falls short (just short) of p4 - use a piece of paper held at 90 degrees to the wing point and then slide it towards the tip of p2. On only 16% of Marsh Warblers is it this short - on the remaining 84% it is level to or longer than p4 (on 1% of 1st winters it is even longer than p3!).

The emargination of p3 on Marsh is nearer the wing tip - falling roughly equal to p7; here it seems to fall at arround p10, and with the length of p2, it tends to confirm a Reed Warbler of some sort. The arguments for fuscus are based on the plumage colour and tone, with greyish and slightly olive tones to the head (like 1st winter Marsh Warbler) and whiter underparts than expected for nominate scirpaceus (hard to tell from the pictures).

Reed Warbler

The primary projection looks long, but is not going to help, I don't think - unless it was trapped and a wing length of 68mm or higher is measured. The length of p2 on fuscus averages shorter than on scirpaceus: on fuscus, 72% fall shorter than p4 in 1st winters and 86% of adults; on scirpaceus, only c.36% have p2 falling shorter than p4. It is not conclusive but gives a bit of support to the plumage features.

How much further we can go on the evidence we have here? I do not know - not much I suspect. However, if it was trapped and feather samples taken we might be able to get a result. If it were to be fuscus, then all of the characters described might have been helpful in future identifications of fuscus; if scirpaceus then we will probebly never be able to identify fuscus in the field in 1st winter plumage.

Reed Warbler

As a final "throw-away" comment, I would suspect that many claims of Marsh Warbler from the second half of October are very likely not. As this bird has shown, there are 1st winter Reed Warblers out there (possibly fuscus) that match Marsh Warbler in all expected ways, but close examination (as here) proves they are not. I have seen a number of birds on the Isles of Scilly claimed (and published) as Marsh Warbler which in my opinion were not - including one published in BB. Be careful, its a dangerous world out there!

As always your opinions are welcome !"


These images are also available in the GB Scarce birds gallery - simply enter "Kelynack" into the location field to deliver a fast search.

(*1) This discussion was first initiated by Julian Hough, CT, through the surfbirds UK rare birds discussion forum. You can catch up on the earlier discussion by joining the group and accessing the archive.