Sí Bheag, Sí Mhór is a well known 17th-century Irish air, composed by the blind harpist Turlough O'Carolan as his first tune. The tune was inspired by a story told to O'Carolan by Squire George Reynolds of County Leitrim. The Squire suggested he write about a mythical battle between two groups of fairies inhabiting two nearby hills: Sí Bheag and Sí Mhór. My arrangement contains variations and countermelodies of the simple tune arranged in three part counterpoint. The original tune contains several imitations of the cherished cuckoo's song which I expand into extended cuckoo duets.