The Purity of Birdsong

Birdsong Sounds Sweeter Because Throats Filter Out Messy Overtones The purity of birdsong is owed in large part to rapid, controlled changes in the shape of the birds' upper vocal tracts, according to a new study of Northern Cardinals by scientists. Their report will appear in next week's (April 4) Proceedings of the National Academy of Sciences. PNAS, Vol. 103, No. 14, 4-Apr-2006 --Indiana University