How strange is this serenade? The Varied Thrush is a robin-sized bird of northwestern rain forests. Its song is nothing like a robin's though. In fact it is unique among North American songbirds. Other birds can produce sounds like this, but no other species deals solely in long "burry or polyphonic whistles" (Pieplow (west):371). A song (a single utterance a few seconds long) usually has some acoustic characteristics and some syntactical ones. (The links lead to articles on each). Syntax refers to the way separate sounds are combined to make a song. But Varied Thrushes use only one sound per song, a long one. Ergo, no syntactical rules for song construction. Acoustically, though, they are tours de force. When you can do that, in so many different ways, why bother with "tweedle-dee, tweedle-dum?" There are syntactical and acoustical rules for combining songs into serenades as well. In this case serenade syntax dictates that each sound be different from the one before it. The acoustical overlay is that each sound should differ noticeably in pitch from the one before it. You can take note of each as the sonogram streams by.
Every winter Varied Thrushes would visit our little homestead at 1100 feet in the hills outside Eugene, Oregon. They spent most of the day foraging in the leaves under the oak trees. Occasionally one would sing a bit from a tall fir, but their efforts were usually desultory, maybe even lacklustre. This sample, though, was, as I dictated, like summer singing, the full show you hear in the higher forests where they nest. I also dictated on that tape that the thrushes are "still here." Clearly they were about ready to go. If you've never done it, you should visit Varied Thrush country in summer. These songs are as emblematic of the rain forests as Canyon Wren songs are of canyons. They fit perfectly with the tall conifers, beard lichen, and cloudy skies.