The Winter Wren (Troglodytes troglodytes), also known as the Northern Wren, is a very small bird, a member of the mainly New World wren family Troglodytidae. It is the only one of nearly sixty species in the family that occurs in the Old World; in Anglophone Europe it is commonly known simply as the Wren, and is the originator of the name. It is noteworthy among songbirds both because of its long and complex songs and because it is one of the few passerine species that has a distribution spanning both North America and Eurasia. It is also highly polygynous, an unusual mating system for passerines.
(From Wikipedia, April 23, 2010)