The brown creeper, also known as the American treecreeper, is a small songbird, the only North American member of the treecreeper family Certhiidae. Only the male sings, and usually only on the breeding grounds, though sometimes during migration as well. His song is a jumble of high, thin notes that lasts up to 1.5 seconds. It’s sometimes likened to singing the phrase trees, beautiful trees. Creepers may join single songs together two or three times in a row. Although the delicate song carries well through the woods the thin, high notes can be easily missed. Males and females make high, wavering call notes that sound like a small chain being dropped into a heap; these notes are noticeably longer than the very short call notes of many other birds. Creepers give these calls all year long and especially while foraging. Their calls can be hard to distinguish from the calls of Golden-crowned Kinglets. They use other variations of calls during flight, courtship chases, courtship feeding rituals, and aggressive interactions. Here is a link so you can listen to the tree creeper itself.