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I am certain what you describe is a Dipper. It is not easy to mistake one. If you had mentioned its short underwater expeditions and the wonderful call (no song in Feb I guess) you'd have got lots of responses already.
It is an interesting thought - that we should all practise this sort of description and sometimes leave our cameras in the bag.
There are lots of very good Naturalists prectising here in iSpot but they might be losing the knack of describing things.
It is worth noting that while the OU was running the now sadly defunct Neighbourhood Nature course (for which iSpot participation was mandatory) they made a point of saying having a camera was not a course requirement and a good description should elicit agreements.
I have agreed with this observation; the description is reasonable and I assume underwater is implicit when Gwyl Taf1 says "...diving, ...".
I am back because I feel it needs emphasising that descriptions are worth a special effort. It is becoming customary for people to post a picture and say NOTHING - bad show. (no-one is listening though!)
I quoted this post here http://www.ispotnature.org/node/315747
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