The Strange Warbler at The Lhen 15 & 16/06/03

By Chris Wormwell

 

 On Sunday 15th. June, Pete Hadfield sent me a photo, which he had taken of an unfamiliar (to him) warbler at the seaward end of the Lhen trench. Unfortunately the bird was very active and Pete’s photo didn’t show the head pattern, but it was enough to set my ‘alarm bells’ ringing.

click on the photo to see a larger image

 The bird was obviously of the acrocephalus family of warblers – long under-tail coverts, emarginated primaries and generally drab colouration.  Of this family, there is only Sedge Warbler that is regular here on the Isle of Man. But this bird was obviously not a Sedge Warbler, due to its very plain mantle and wing feathers (Sedge Warbler has a distinctly streaked mantle and dark centres to the wing coverts and tertials). That left me having to consider that the bird was either a Reed Warbler (a rare passage bird on the island) or the even rarer Marsh Warbler (no records, from the main island) and therefore definitely worth further investigation. I must admit that my initial reaction was to lean towards the bird being a Marsh Warbler as it appeared to lack any warm colouration (although this was subjective from one photo) and had very pale legs. Pete also mentioned that bird was frequenting the bracken and brambles in the area rather than the nearby phragmites bed, which also lent credence to my Marsh Warbler theory (Reed Warblers are almost exclusively a reedbed species).

 Pete then really set the cat amongst the pigeons by releasing a second photo of the bird which revealed it to have a very strong, flared supercillium, dark eye-stripe and dark edges to the crown. This threw the Reed/Marsh theory right out of the window, as neither species show these characters. I now had to consider a serious rarity – Paddyfield Warbler. Fortunately, from the photo, I could clearly make out the length of the primary projection (the amount by which a bird’s primary flight feathers extend beyond the secondaries on the closed wing) and they were just too long for Paddyfield Warbler. Also, Paddyfield has a longer tail, which is exaggerated by their short-ish primary projection.

click on the photo to see a larger image

 Some discussion then took place on the excellent Bird Forum website http://www.birdforum.net/ and the best that we could come up with was that it was some kind of hybrid between Sedge and Marsh/Reed Warblers. There was a further, more exciting possibility of it being an eastern species called Black-browed Reed Warbler, but as this species has never been recorded in Europe (let alone the IOM!) it was just too fanciful – plus, I knew very little about that species’ field characters.

There was only one thing for it, I had to go and see if the bird was still present and to see if I could get any more helpful photos/notes on the bird.

After a hairy 7 mile drive through back lanes of the northern plain of the island, I arrived on site and could immediately hear several Sedge Warblers, Whitethroats and a Grasshopper Warbler singing from the area. There was nothing out of the ordinary singing from where Pete had directed me to.

After about 15 minutes of looking at ‘classic’ Sedge Warblers, I noticed a bird that was singing from a patch of bracken some 50 yards away. I set the ‘scope on the bird and, even though it was facing away from me, I was immediately struck by it’s plain appearance. I then also noticed that several of the phrases it was using in it’s song ‘belonged’ to other species! House Sparrow, Chaffinch, Swallow and Pied Wagtail phrases were all ‘thrown in’ at regular intervals along with what sounded like the more usual Sedge Warbler phrases. Eventually the bird turned sideways-on to me and revealed it’s head pattern – just as it appeared in Pete’s second photo. However, what Pete’s shot didn’t show was that it had a really long (compared to Sedge Warbler) bill.

click on the photo to see a larger image

The bird was completely ignored by the other singing warblers and at one stage even shared a song perch with a ‘Sedgey’. This now showed me how much bigger the bird was than Sedge Warbler (I’d estimate 10% to 15% in length and more ‘pot-bellied’).

Prolonged views allowed me to study the head pattern and, whilst reminiscent of Sedge Warbler, the crown wasn’t as dark and only really extended from the base of the bill to approximately a ¼ of the way back. There was a clear dark border to the upperside of the supercillium (which flared behind the eye). The rump appeared to be more warmly coloured than the rest of the upperparts, which had none of the olive tones often associated with Marsh Warbler.

click on the photo to see a larger image

Given all this evidence, I can only assume that the bird was (and may well, still be!) a hybrid – most likely between Sedge Warbler and Reed Warbler.

I must thank several people on the Bird Forum website for their valued input, in particular; Michael Frankis, Darrell Clegg, Simon Woolley and Harry Hussey. Also the several people who replied to my request for help on the Surfbirds http://www.surfbirds.com/ website.