A tale of the Sulphur-bellied Warbler on the island of Christiansø
Christiansø in the Baltic Sea is one of the best Danish sites for rare birds. Egyptian nightjar, Rufous-tailed Robin, Swainson’s Thrush, Siberian Rubythroat and Siberian Accentor have all been recorded here within the last 35 years. But on the 30th may 2016 an even rarer bird appeared on the island!
I arrived on Christiansø by boat at 1100 for my annual "I-need-to-find-rare-birds-or-I-will-surely-die-vacation".
It was quite a hot day with a steamy mist around the island. Already after a few hours I managed to locate a singing Blyth’s Reed Warbler at the southend close to “Slottet”. It was quite a good find and I immediately called Peter Lyngs who was also on the island, to tell him about the bird. Shortly thereafter, I noticed a small bird calling with a peculiar “djep” – somewhat similar to a single call of a distant Bearded Tit or the soft call of a Radde’s Warbler. I turned to find a small Phylloscopus warbler perched in a small bush. The yellow supercillium and pale legs led me to believe it was just a Willow Warbler and I quickly turned my attention back on the singing Blyth’s. Peter Lyngs soon appeared but again the Phyllosc called. This time it flew past us up in a nearby tree.
“That’s a weird call for a Willow Warbler” I said. “A Willow Warbler surely can’t call like that!”, Peter replied. We now noticed that the yellow supercillium seemed profoundly longer than on Willow Warbler and was especially bright in front of the eye. The bird kept calling and left us utterly confused. Both of us are familiar with pretty much all of the Western Palearctic species of Phylloscopus – but this bird didn't match any of them!
After a couple of minutes, the bird started singed. The song sounded a bit like that of Lesser Whitethroat or perhaps Linnet, which only added to our confusion!
Lars Christansen, Anders Myrtue and Hans Ole Mathiessen joined us, but found themselves equally ignorant of the birds ID.
Arctic Warbler and Radde’s warbler were discussed but could both easily be ruled out. And it didn't take us long to realize that the bird might actually be something very, very rare. To confident in our own birding skills or perhaps because of lack of ambition, we had however neglected to bring literature on the rarer Asian Phylloscs to Christiansø. Instead we tried to get some photos of the bird and record the call and song. I got some decent shots of the birds head and started texting the photos to other birders. Most of them had no idea what the bird was, but were all eager to help distributing the photos to other birders. Meanwhile I desperately started checking Xeno Canto for pretty much every rare Asian warbler-species I could possibly think of. Tickells, Yellowstreaked, Tytlers, Pale-legged leaf were all checked but obviously wrong - and I struggled to remember the English names for all the different Phyllosc-species, when decent help finally arrived!
My old friends Henrik Haaning Nielsen and Troels Eske Ortvad had seen my photos and both suggested the bird could be a Sulphur-bellied Warbler. I remembered having seen that species in India and that it actually had had a supercillium like our bird. A quick check of the call and song on xeno canto proved to be a perfect match!
It was indeed a Sulphur-bellied Warbler and although I kept thinking “It can’t be – it’s to bloddy impossible!” – there were no doubt about it. Luckily the bird was quite confiding and kept singing frequently the rest of the day. We even got some good photos and decent song-recordings.
The bird was again present on the 31st may and seen by 25 visiting twitchers. Tomorrow we expect even more to come and visit this Western Palearctic first. And if anyone should feel the urge to see this exclusive LBJ, you’re all very welcome.
Kind regards Sebastian Klein