Black-crested titmouse
Chapter 10: More birds! More Sounds!
Subchapter: More birds! More Sounds!—Americas
From page 169 in the book.
The titmice illustrate well the "species problem." It was not a unanimous decision in 2002 to recognize the black-crested titmouse of central Texas and northern Mexico as a species different from the tufted titmouse. The singing behavior of these two birds seems indistinguishable: Songs are similar, both have smallish song repertoires and sing with "eventual variety," and neighboring males match each other's songs.
♫694. Sound like a tufted titmouse? I think so, but it's not. Hear the matched countersinging, with a bird in the background singing the same song as the near bird? I hear (and see in Raven Lite) the distant bird at 0:04, 0:18, 0:29, 0:35, and more. At 1:40 the foreground titmouse does what you'd expect a tufted to do, switch to a new song; listen closely, and you'll hear the background bird also singing this new song (perhaps most evident at 3:08 and 5:10). Enjoy also the black-and-white warbler singing in a much higher register.
April 12, 2013. Kerr Wildlife Management Area, Hunt, Texas. (5:41)