BIRD GUIDING AROUND OSLO

Friday, 10 June 2016

Mystery acro warbler

There are number of Hedmark Installments to come (I’ve discovered by the way that as a Brit I should spell it “instalment” and that “ll” is the US way but I think the double l looks better so I will stick with it!) but here is something completely different.

Since Per Christian and I heard 2 singing Blyth’s Reed Warblers last Thursday night at Skjerven in Maridalen there have been a number of other reports of these birds but also of Marsh Warblers in the same place and of course one begins to wonder how many birds have actually been there (a bit like the situation at Torp where Per Christian and I didn’t have Blyth’s and only Marsh but others have had the opposite). My attempts to record the Blyth’s Reeds were irritatingly unsuccessful due to distance (and the noise of the Grasshopper Warbler) but a (typical) Marsh Warbler was recorded there a couple of days later.
I haven’t had a chance (or the energy after my Hedmark exertions) for another nocturnal outing in Maridalen (there has also been quite a bit of wind) but yesterday and today I made daytime visits to Maridalen. I didn’t try to locate the birds at Skjerven (where close access is not possible) but instead went to Nes. Here a warbler was recorded on Saturday night that was initially reported as a possible Blyth’s Reed but I heard the recording and reckoned it was an Icterine and what I believe is the same bird has since been reported as a Marsh! The bird is in exactly the same place as last year breeding Blyth’s Reed and where a Marsh Warbler sang the year before. There are also Icterine Warblers nearby. The middle of the day is not the best time for these species but a bird was singing when I got there yesterday. It was singing 3-5 metres up in bushes and trees and was incredibly difficult to see. I got to see it a few times in flight and also saw there was another bird with it which I saw in l flight a couple of times (presumably a pair). In flight they were clearly not Icterine Warblers but I found/find the song difficult. It is clearly similar to both Marsh and Icterine Warbler (but these songs are to my unmusical ears quite similar anyway) but I also think it was missing some of the scratchy elements of Marsh Warbler song and there were associations to Blyth’s Reed including the tacking notes. I eventually got to see the bird poorly singing and it had a fairly noticeable supercilium which extended behind the eye, seemingly very short primary projection, what appeared to be plain coloured tertials and primaries and I saw no white tips to the outer tail feathers when I flight. The colour of the upperparts was also quite cold and brown. My views were brief but the video captures most of these details.  I never saw the non-singing bird well so who knows what this one is!

What I found strangest with this bird was that it often sang high up in trees something that I have never experienced with Marsh Warbler before but have with Blyth’s and it repeatedly sang from exactly the same bush that last year’s male Blyth’s favoured. It did however also sing from the new growth reeds in the area a few times but both the Blyth’s Reeds and Marsh Warblers at this site have sung here. It is also my experience that Marsh Warblers are normally much less shy than Blyth’s Reed and easier to see whereas this bird was exceptionally skulky and also flew off whenever I tried to get closer and see it.

So what is this bird (and also its mate)? It is definitely not a pure Blyth’s Reed Warbler but I have big problems with it being a pure Marsh Warbler. A hybrid between the two is therefore a plausible solution. This hybrid pairing is said to occur in the fringe areas of the range of Blyth’s and with both Marsh and Blyth’s Reed having sung at this same location in previous years it is tempting to think that it was born here. Better pictures will help.

Today I visited again hoping to take some better pictures. I heard an acro singing 200m west of where I had yesterday’s bird and this bird sounded and acted (kept low) like a Marsh. It was skulky but less so than the other bird and I was able to see the “kind” face of a Marsh Warbler and in flight the white outer tail feathers were noticeable (these, the long primary projection and pale edged primaries and tertials are all visible in the one picture I managed). I also thought that there may have been two birds here. So this couldn’t possibly be yesterday’s bird, could it? As I walked on I was relieved (!) to hear the other bird singing in the same place as yesterday. Again it was incredibly skulky and I only saw it in flight. And again it sang high up in bushes and trees (but also from the reeds). The difference in behaviour between the two birds was noticeable and the songs were also clearly different. There is much individual variation amongst Marsh Warblers but the “classic” bird had lots of tit sounds in its repertoire which are missing from the mystery bird. My money is still on the mystery bird being a Marsh x Blyth’s Reed hybrid…. But I guess only a feared ringer and a DNA test will prove it for certain J
 



 
 
the only picture I managed of either of the warblers. This is the classic Marsh Warbler and here you can see the pale corners to the tail, long primary projection and pale edges to primaries and tertials all of which appear to be missing on the other bird

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