My Chiffchaff puzzle may have become a bit clearer today. With only a short period of time available for birding I headed to Bygdøy just before 2pm. I tried playing the songs of Common and Siberian Chiffchaff (gransanger) from the car hoping this would attract the birds and give me good views. It didn't!
Switching to plan B I got out of the car. A few Blue Tits (blåmeis) and Wrens (gjerdesmett) made their presence known so I concentrated on them knowing that the Chiffchaffs have often been with these birds. And sure enough there was a Chiffchaff there, and it was brown. This bird was a classic tristis with tobacco brown ear coverts, brown mantle and just some olive edging to the wing feathers. It was quite close but amongst the grass and gave good but brief views through the bins but no chance of pictures. It moved off into the reeds and then a tristis call came from where it was but without me seeing who gave it. This might help explain my experiences of the last two days if the tristis has been present all the time and calling but I just haven't seen it. I recorded this call and the sonogram is a bit clearer than previous ones and just shows a flat line which is a good match for tristis. I see though that I still have work to do: I need to record the call of a bird (ideally all of them that have been present) I see calling and capture it all on video auch that the bird and its call can be linked.
Two Sparrowhawks flew in and took prey (one being most likely a Blue Tit) whilst I was there so the Chiffchaffs have more than just the weather to contend with.