Wren

Eurasian-Wren by Andreas Trepte - Own work. Licensed under CC BY-SA 2.5 via Wikimedia

I don't know about you, but over the last week or so I've gradually realised that the bird I most often hear singing is the wren, Troglodytes troglodytes. I'm sure I read somewhere that the wren is Britain's commonest bird, which is odd when you consider how infrequently you get a good view of one. 
The male wren builds several nests in a bid to impress potential mates. If a female decides that one is suitable she moves in and finishes off lining it ready for egg laying.
But the most remarkable thing about wrens is the incredible power of their song. The decibel to weight ratio must knock the pants of every other bird; it is just incredibly loud. It is also very distinctive, with its intermittent trills and fluty cadences. 
Britain has four distinct subspecies of wren: the St Kilda wren T. t. hirtensis; the Fair Isle wren T. t. frideriensis; and the Shetland wren T. t. zetlandicus; the common subspecies T. t. indigenus.