The wrens are mostly small, brownish passerine birds in the mainly New World family Troglodytidae. There are approximately 80 species of true wrens in approximately 20 genera. Only the Eurasian Wren occurs in the Old World, where in Anglophone regions it is commonly known simply as the “wren” as it is the originator of the name. The name wren has been applied to other, unrelated birds, particularly the New Zealand wrens (Acanthisittidae) and the Australian wrens (Maluridae).
Most wrens are small and rather inconspicuous, except for their loud and often complex songs. Notable exceptions are the relatively large members of the genus Campylorhynchus, which can be quite bold in their behavior. Wrens have short wings that are barred in most species, and they often hold their tails upright. As far as known, wrens are primarily insectivorous, eating insects, spiders, and other small arthropods, but many species also eat vegetable matter and some will take small frogs and lizards.
The English name wren derives from Middle English wrenne, Old English wraenna, attested (as werna) very early, in an 8th-century gloss. It is cognate to Old High German wrendo, wrendilo and Icelandic rindill (the latter two including an additional diminutive -ilan suffix). The Icelandic name is attested in Old Icelandic (Eddaic) rindilþvari. This points to a Common Germanic name *wrandjan-, but the further etymology of the name is unknown.
The wren is also known as kuningilin “kinglet” in Old High German, a name associated with the fable of the election of the “king of birds”. The bird who could fly to the highest altitude would be made king. The eagle outflew all other birds, but he was beaten by a small bird who had hidden in his plumage. This fable is already known to Aristotle (Hist. animalium 9.11) and Plinius (Naturalis hist. 10.74 ), and was taken up by medieval authors such as Johann Geiler von Kaisersberg, but it concerns Regulus, and is apparently motivated by the yellow “crown” sported by these birds (a point noted already by Ludwig Uhland). In modern German the name is “Zaunkönig”, king of the fence (or hedge). In Dutch the name is “winterkoninkje” (little winter king).
The family name Troglodytidae is derived from troglodyte, which means “cave-dweller”, and the wrens get their scientific name from the tendency of some species to forage in dark crevices.
The name “wren” is also ascribed to other families of passerine birds throughout the world. In Europe, species of Regulus are commonly known as “wrens”, the Common Firecrest and Goldcrest as “fire-crested wren” and “golden-crested wren”, respectively.
The 27 Australasian “wren” species in the family Maluridae are unrelated, as are the New Zealand wrens in the family Acanthisittidae, the antwrens in the family Thamnophilidae, and the wren-babblers of the family Timaliidae.
Wrens are medium-small to very small birds. The Eurasian Wren is among the smallest birds in its range, while the smaller species from the Americas are among the smallest passerines in that part of the world. They range in size from the White-bellied Wren, which averages under 10 centimetres (3.9 in) and 9 grams (0.32 oz), to the Giant Wren, which averages about 22 centimetres (8.7 in) and weighs almost 50 grams (1.8 oz). The dominating colours of their plumage are generally drab, composed of grey, brown, black and white, and most species show some barring, especially to tail and/or wings. There is no sexual dimorphism in the plumage of wrens, and little difference between young birds and adults. All have fairly long, straight to marginally decurved bills.
Wrens have loud and often complex songs, sometimes given in duet by a pair. The song of members of the genera Cyphorhinus and Microcerculus have been considered especially pleasant to the human ear, leading to common names such as Song Wren, Musician Wren, Flutist Wren and Southern Nightingale-
Wrens are principally a New World Family, distributed from Alaska and Canada to southern Argentina, with the greatest species richness in the Neotropics. As suggested by its name, the Eurasian Wren is the only species of wren found outside the Americas, as restricted to Europe, Asia and northern Africa (it was formerly considered conspecific with the Winter Wren and Pacific Wren of North America). There are a number of insular species, including the Clarion Wren and Socorro Wren from the Revillagigedo Islands in the Pacific Ocean, and the Cobb’s Wren in the Falkland Islands, but few Caribbean islands have a species of wren, with only the Southern House Wren in the Lesser Antilles, the Cozumel Wren of Cozumel Island, and the highly restricted Zapata Wren in a single swamp in Cuba.
The various species occur in a wide range of habitats, ranging from dry, sparsely wooded country to rainforest. Most species are mainly found at low levels, but members of the genus Campylorhynchus are frequently found higher, and the two members of Odontorchilus are restricted to the forest canopy. A few species, notably the Eurasian Wren and the House Wren, are often associated with humans. Most species are resident, remaining in Central and South America all year round, but the few species found in temperate regions of the Northern Hemisphere are partially migratory, spending the winter further south.
Wrens vary from highly secretive species such as those found in the genus Microcerculus to the highly conspicuous genus Campylorhynchus, the members of which will frequently sing from exposed perches. The family as a whole exhibits a great deal of variation in their behaviour. Temperate species generally occur in pairs, but some tropical species may occur in parties of up to twenty birds.
Wrens build dome-shaped nests, and may be either monogamous or polygamous, depending on species.