Apologies if this description is a bit vague but I was on the verge of photographing my mystery bird and was interrupted by a cyclist so any help appreciated! This was a brown bird somewhere between blackbird and collared dove in size, it was seen by a stream in woodland on the Irwell and was darting rapidly up and down across the water before perching by the waterside. The only distinguishing feature I managed to spot before being interrupted was a clear white spot in the style of a cormorant's. Has anybody any idea what I might have seen?