Unusual behaviour of a Sakhalin Leaf Warbler - presumably health related

Of the huge number of Sakhalin Leaf Warblers on Tsushima this spring, the behaviour of this bird stood out and remains a bit of a puzzle. I can only imagine it wasn't healthy but I've no idea what could have been wrong with it.


It was present on two consecutive days but apparently gone on the third after a general clear-out of warblers. It was very approachable on the ground but when it flew it did so strongly giving no hint of any problem. It occasionally flew up into overhanging bushes but mostly it sat somewhere along a 100 metre stretch of roadside verge. We saw it several times that day as the road, along a steep hillside, was an excellent birding spot which we returned to regularly. The bird was always easily picked up on arrival because it was so vocal, which isn't something I'd normally associate with sick individuals. The second day it was mostly in the trees on the downward slope from the road and seemingly feeding well abundance of caterpillars. Looking at the images I have of the bird, I'm now struck that none show legs, it's always sitting. If it had a problem with feet/legs, this may account for it nevertheless being vocal, feeding well and flying strongly.


However, it also had a colour aberation which I presume was due to the onset of whatever health problem it was suffering from. At a glance it could give the impression of having a narrow white rump patch but as can be seen in the following images there was also a faint greyish wash on the back and some lesser wing coverts suggesting perhaps that pigmentation production ceased as these feathers were growing.

It almost looks like a ground nester here, in the leaf litter it habitually kept its tail cocked like this.

In a more open situation it fanned and pumped its tail. Of course Sakhalin do pump their tails anyway but this was very pronounced.

Just once it flopped down in this abnormal position revealing the 'white rump' and pigment deficient feathers on back and lesser wing coverts.

The second day it was in the trees the whole time, and feeding well, but the continuous, vigorous tail pumping was only more apparent in that situation.



Periods of sitting still on a branch vigorously pumping its tail was very different behaviour to the many other Sakhalin Leaf which were very active.

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The next couple of images have nothing to do with this post but I want to tag them on anyway. The former I want to post because it's my best ever shot of this heron species and the latter because the nest is such an amazing structure.

Probably my best ever shot of this rather scarce heron. This is only the second Striated I've seen this year.

Perhaps a case of an ever-growing nest crushing the bush beneath it but I prefer to think this is a very traditional Osprey site which over time is creating its own micro-environment on top of the bare off-shore stack.