Villancico has gained some modern notoriety as a Christmas carol.
Attributed by some sources to Mateo Flech in others described as anonymous.
The song bears a strong resemblance to the villancico `Falalanlera` written by the Aragonese Bartomeu Carceres.

The apparently nonsensical syllables `ríu ríu chíu` are often interpreted as representing the nightingale`s song.
The main theme of the song is the Nativity of Christ and the Immaculate Conception.
The refrain that gives Villancico its name is
Ríu ríu chíu la guarda ribera
Dios guardó el lobo de nuestra cordera.
`Ríu ríu chíu the kingfisher God kept the wolf from our Lamb.`

https//en.wikipedia.org/wiki/Ríu_Ríu_Chíu