When visiting Quintana Sanctuary I observed one Prothonotary Warbler taking this pose for a longer moment when perching on a sunny branch.

Can anybody tell me what kind of behavior is that. Do you see it often? I do not spend much time with warblers, except migration time. This was done by the bird not by the wind. Bird spread its flank feathers wide open (like you can see on photo) and hold them spread for several seconds then put them back to 'normal' position. I had a thought of maybe sunbathing but never heard of warblers doing this. So far nobody gave me any possible explanation for this behavior.


Thanks for any information.