Wren Day, also known as Wren's Day, Day of the Wren, or Hunt the Wren Day (Irish: Lá an Dreoilín), is celebrated on 26 December, St. Stephen's Day. The tradition consists of "hunting" a fake wren and putting it on top a decorated pole. Then the crowds of mummers, or strawboys, celebrate the wren (also pronounced wran) by dressing up in masks, straw suits, and colourful motley clothing. They form music bands and parade through towns and villages. These crowds are sometimes called wrenboys.
In past times and into the 20th century, an actual bird was hunted by wrenboys on St. Stephen's Day. The captured wren was tied to the wrenboy leader's staff or a net would be put on a pitchfork. It would be sometimes kept alive, as the popular mummers' parade song states, "A penny or tuppence would do it no harm". The song, of which there are many variations, asked for donations from the townspeople. Often the boys gave a feather from the bird to patrons for good luck. The money was used to host a dance or "Wren Ball" for the town on a night in January. Wrenboys would go from house to house in the countryside collecting money but in the towns the groups were more organised and there was often an element of faction-fighting. In both cases there would be a Wren Captain, usually wearing a cape and carrying a sword; musicians; strawboys and others dressed as old women or other things. It is a day of wild revelry and people usually conceal their identities so they can play tricks on their friends. This type of behaviour is typical of Celtic festivals as a sort of purge. The band of young boys has expanded to include girls, and adults often join in. The money collected from the townspeople is usually donated to a school or charity.
Similar traditions of hunting the wren have been performed on the Isle of Man on Boxing Day and in Pembrokeshire, Wales on Twelfth Day (6 January) and, on the first Sunday of December in parts of Southern France, including Carcassonne.  The custom has been revived in Suffolk by Pete Jennings and the Old Glory Molly Dancers and has been performed in the village of Middleton every Boxing Day evening since 1994.
The Celtic Theory
The wren celebration may have descended from Celtic mythology. Ultimately, the origin may be a Samhain or midwinter sacrifice and/or celebration, as Celtic mythology considered the wren a symbol of the past year (the European wren is known for its habit of singing even in mid-winter, and its name in the Netherlands, "winter king," reflects this); Celtic names of the wren (draouennig, drean, dreathan, dryw etc.) also suggest an association with druidic rituals.
Lleu Llaw Gyffes, a Celtic hero, wins his name by hitting or killing a wren. He strikes a wren "between the tendon and the bone of its leg", causing Arianrhod, his mother, to say "it is with a skillful hand that the fair-haired one has hit it". At that Gwydion, his foster father, reveals himself, saying Lleu Llaw Gyffes; "the fair-haired one with the skillful hand" is his name now".
The Christian theory
The myth most commonly told in Ireland to explain the festival is as follows; God wished to know who was the king of all birds so he set a challenge. The bird who flew highest and furthest would win. The birds all began together but they dropped out one by one until none were left but the great eagle. The eagle eventually grew tired and began to drop lower in the sky. At this point, the treacherous wren emerged from beneath the eagle's wing to soar higher and further than all the others. This belief is shown is the song that begins:
"The wren, the wren, the King of All Birds, St. Stephen's Night got caught in the furze."
This also illustrates the tradition of hunting the wren on Christmas Day (St. Stephen's Eve/Night)
The Norse theory
The tradition may also have been influenced by Scandinavian settlers during the Viking invasions of the 8th to 10th centuries though it is usually attributed to the "Christianising" of old pagan festivals by saints to ease the transition and promote conversion.Various associated legends exist, such as a wren being responsible for betraying Irish soldiers who fought the Viking invaders by beating its wings on their shields, in the late 1st and early 2nd millennia, and for betraying the Christian martyr Saint Stephen, after whom the day is named. This mythological association with treachery is a possible reason the bird was hunted by wrenboys on St. Stephen's Day, and/or why a pagan sacrificial tradition was continued into Christian times. Despite the abandonment of killing the wren, devoted wrenboys continue to ensure that the Gaelic tradition of celebrating the wren continues, although it is no longer widespread.
In Galicia, Spain, the Caceria del rey Charlo (Chase of King Charles) was performed. The inhabitants of Vilanova de Lourenza would chase down a wren and, after tying it to a pole, would parade it and show it to the abbot of the local monastery, who would then to offer them food and drink and appoint two leaders of the local town council out of the four candidates proposed by townsmen. This tradition has been recorded since the 16th century. The sources are somewhat misleading about the day, since they call it "New Year`s Day" but might mean "The day after Christmas", which was regarded then as the end of the year. It is also commonly practised in Ireland by children aged from (8-15)
In 1955 Liam Clancy recorded "The Wran Song" ("The Wren Song"), which was sung in Ireland by wrenboys. In 1972 Steeleye Span recorded "The King" on Please to See the King, which also reflects the tradition. They made another version, "The Cutty Wren", on their album Time. "Hunting the Wren" is on John Kirkpatrick's album Wassail!. The Chieftains made a collection of wrenboy tunes on The Bells of Dublin. In the song "The Boys of Barr na Sráide", which is based on a poem by Sigerson Clifford, the wren hunt is also prominent.
"The Wren [Wran] Song" is also on the Clancy Brothers and Tommy Makem's 1995 album Ain't It Grand Boys: A Collection of Unissued Gems, as the last song in "Children's Medley". The spoken introduction tells how as boys they would go out on Christmas Day and kill a wren, and on the next day, St. Stephen's Day, they would go from house to house singing this song and asking for money "to bury the wren".
- "Christmas and New Year in Ireland Long Ago".
- Something for everybody (and a garland for the year) by John Timbs, 1861. pp. 152-155
- The Golden Bough by James George Frazer, NuVision Publications, LLC, 2006, ISBN 1-59547-959-7, ISBN 978-1-59547-959-4. pp.294-295
- "old Glory & The Cutty Wren" by Pete Jennings.
- The British and European symbolic hunting of the Eurasian wren is investigated by Elizabeth Atwood Lawrence, Hunting the Wren: Transformation of Bird to Symbol (University of Tennessee) 1997.
- "La cacería del reyezuelo: análisis de una cacería ancestral en los países célticos" by Fernando Alonso Romero at Anuario Brigantino, issue 24, 2001
- Example:"The Wren The Wren", Celtic Tradition , Amiga, 1987.
- "Ain't it Grand Boys: A Collection of Unissued Gems", the Clancy Brothers and Tommy Makem, Columbia Records, 1995. Children's Medley, ibid.
- Archived audio recording of The Wren Song, sung by Will Murphy, Colliers, Newfoundland
- Discussions about the Wren song
- Recording of the Wren dance/song on the Isle of Man
- Handbook of Birds of the World: Wrens family account
- Hunting the Wren on the Dingle peninsula - An excellent account of the origins, history, contemporary aspects and international connections of the wren.
- Hunt the wren in the Isle of Man
- The Weird Side of St. Stephen's day in Ireland & Elsewhere (Fustar.info)
- Wren Boy Festival
- Wren Day
- Wren Day Songs