The Eurasian wren (Troglodytes troglodytes) or northern wren is a very small insectivorous bird, and the only member of the wren family Troglodytidae found in Eurasia and Africa (Maghreb). In Anglophone Europe, it is commonly known simply as the wren. It has a very short tail which is often held erect, a short neck and a relatively long thin bill. It is russet brown above, paler buff-brown below and has a cream buff supercilium. The sexes are alike.
The species was once lumped with Troglodytes hiemalis of eastern North America and Troglodytes pacificus of western North America as the winter wren. The Eurasian wren occurs in Europe and across the Palearctic – including a belt of Asia from northern Iran and Afghanistan across to Japan. It is migratory in only the northern parts of its range. It is also highly polygynous, an unusual mating system for passerines.
The Eurasian wren was described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Motacilla troglodytes. The specific epithet is from the Ancient Greek trōglodutēs meaning "cave-dweller". In 1555 the German naturalist Conrad Gessner had used the Latin name Passer troglodyte for the Eurasian wren in his Historiae animalium. The species is now placed in the genus Troglodytes that was introduced by the French ornithologist Louis Pierre Vieillot in 1809.
The Eurasian wren was formerly considered conspecific with two North American species: the winter wren (Troglodytes hiemalis) and the Pacific wren (Troglodytes pacificus). Some ornithologists place the Eurasian wren, the winter wren and the Pacific wren in a separate genus Nannus that was introduced by the Swedish naturalist Gustaf Johan Billberg in 1828 with the Eurasian wren as the type species.
Common but inconspicuous in woodland habitats with dense undergrowth, gardens, farmland hedgerows, heathland and coastal cliffs. It usually sings from a fairly exposed perch, but on other occasions it behaves like a mouse, moving between the brambles and undergrowth. It is easily identified by its small size, brown plumage, and the habit of keeping its tail elevated. It is heard more frequently than it is seen. The song is powerful and lively with a diverse series of repeating trills and chirps.