Eurasian Wren
Troglodytes troglodytes

The Wren is on the smallest birds in Britain at just 9 - 10.5 cm in length, but makes up for its diminutive size with its explosive song. They can usually be found darting about in undergrowth and gardens where they feed on insects and other invertebrates. While very common, they can decline sharply in very cold winters, during which they may often form communal roosts in holes and nest boxes to keep warm. They are closely related to the Pacific and Winter Wrens of North America and were until recently all included as the Winter Wren. There are many subspecies of the Eurasian Wren in Europe, often with isolated island populations being darker in colour, or having longer bills.
 

1: Wokingham, Berkshire, 19/12/2012.