This is an Abert's Towhee doing what I call "Towhee Talk". This is a type of call that all species of Towhees that I'm familiar with sing. I noticed while looking at the spectrogram of this call that it is in all probability two towhees singing together (sometimes called "duetting"). I do notice that they sing this song when there are several together in one bush. This one was recorded at Peck's Lake [Arizona], Nov. 4, 1997. See for a spectrogram of the central part of this sample - see if you think it's two birds, too. (Remember to press "back" after viewing the image)
Douglas Von Gausig (recordist; copyright holder), Naturesongs.com
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