Definition and background:
Aerophone, Edge-blown Aerophone, Percussion instrument, Auxiliary Percussion This instrument is a special effect that creates a sound similar to the whistle of a bird. The bird whistle is a hand-held mouth-blown instrument that can be made out of metal, wood, or plastic. They are created like a simple closed flue pipe with a tube leading to a sharp lip ( labium) that splits the air stream to create the whistle sound. The tube then leads to a chamber with water. The air is forced to agitate the water and produce a high- pitched gurgling sound that combines with the whistle to imitate the chirping of a bird. A screw on the top of the chamber can be used to adjust the degree of water agitation and change the quality of the sound to have more or less chirping quality. The sound of a bird whistle can closely approximate the sound of a number of bird species with an experienced performer. In most cases however, it is the generic sound of a bird that is important and there are very few compositions that expect a specific bird call. The bird whistle can provide sounds with rhythmic accuracy when necessary. The bird whistle has no way of easily altering or adjusting pitch with any accuracy, so there is no range, nor is there any specific pitch or set of pitches associated with the instrument. A composer can provide direction for higher or lower pitch. Also [Eng.] Bird Whistle; [Fr.] Sifflet d'oiseau; [It.] Gli Uccelli; [Ger.] Vogelpfeife.
For more information on the music term "Bird whistle" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary