"Yes it certain is a Siberian Flycatcher – small, largely dark bill; folded primaries reaching as far as the tip of the longest uppertail coverts but no further; rather retarded moult with still a few juvenile feathers on its rear head, nape, lower back and uppertail coverts (Asian Brown almost never show so many retained juvenile feathers in their upperparts, Grey-streaked very rarely) – but that said it is surprisingly advanced for a first calendar year bird.
If any more was needed the dark centres to its undertail coverts are diagnostic for Siberian Fly.
