Here's the song, sung in the Ponderosa Pines near the top of Oak Creek Canyon of Central Arizona, 4/10/99. The song is so high (between 4500 and 8000Hz) that many humans just can't hear it at all!
Brown Creepers (Certhia americana) are known as the ultimate recluse - unobtrusive, and the epitome of a quiet existence, they sing seldom, "peep" this very high-pitched peep occasionally. This recording, made on San Juan Island in Washington state, is from 20 feet with a parabolic mic - very quiet! 1
