– W. L. Dawson, The Birds of California, 1923

If you spend much time in the Sierra (or in the Cascades, for that matter) you will hear the bright, happy song of the “Thick-billed” Fox Sparrow (or Passerella iliaca megarhyncha). Individuals have repertoires of just a few different song types (typically three or more) which they alternate between like the example below (my recording from western El Dorado County, California),

This bird sang one of its song types…

…followed by a different song type…

…then the first song type repeated…

---then the second song type repeated.

These sparrows share a truly remarkable skill along with many other songbirds, the ability to reproduce a complex, rapidly varied song with stunning precision. To demonstrate this, the next two videos lack sound and animation to allow you to focus on the spectrogram itself. The video below shows one rendition of song type one which, midway through the video, fades out and is replaced with the spectrogram of the second rendition of this song type. The fade is difficult to detect because each rendition is so precisely matched. You may only be able to see it by watching the text heading as it changes. It may take a couple of viewings to fully appreciate how perfectly this song is reproduced.

And just to hammer this point home, here is an overlay of the first rendition of the second song type over the second rendition of that same song type.

Just imagine the complex set of motor skills at work here to produce this song…rapid adjustments of the syrinx (avian equivalent of our larynx) and precise breath control…then to be able to reproduce that set of adjustments perfectly!

The best analogy to a human endeavor I could come up with is: shooting free throws in basketball. The basket is the same distance away, the hoop the same diameter, the ball is the same size and weight. And yet, in spite of amazing athletic skill and thousands of hours of practice, the best NBA players miss one out of ten…and that with a margin of error provided by the hoop being larger than the diameter of the ball.

Evidence from genetic and other characters is mounting to suggest that there are actually multiple species of Fox Sparrow. The case for Thick-billed is among the strongest and their vocalizations bolster that case.

Imitations: Thick-billed Fox Sparrows frequently incorporate imitations of other birds’ song into their songs, something rarely observed in other subspecies (see Garrett et al. 2000 Birding 32:412, Pieplow 2019 Field Guide to Bird Sounds of Western North America). With some patience (and sometimes, a bit of imagination) one can often find these imitations in nearly every song. Below are some examples from my recordings.

Here is a different (third) song type from the same bird in the earlier examples. It includes an excellent imitation of a common call of the American Robin.

Here is it again with the “robin” section highlighted.

And here is that section, by itself.

Here is a recording I made in Sierra County, California of a Fox Sparrow including what, to my ear, sounds like the common “tic-eeer” call of a Rock Wren. That part is right at the end of the song.

Highlighted:

Isolated:

And just to add one more possibility, I’d consider that ringing trill just before the “Rock Wren” call, a pretty good imitation of a Dark-eyed Junco song…

Unique Call Note: The most common call note of Thick-billed Fox Sparrows is completely unlike the call of the other Fox Sparrow subspecies (see Garrett et al. 2000 Birding 32:412, Pieplow 2019 Field Guide to Bird Sounds of Western North America).

All the subspecies except P. i. megarhyncha give some version of a loud “smack” note like this example of from a “Sooty” Fox Sparrow I recorded at Pt. Reyes, California in winter.

Thick-billed Fox Sparrows give a metallic call note, not unlike that of the California Towhee. This recording from Placer County, California.

This is just one more example of how careful listening to what the birds have to say can produce entertainment, awe, and teach us something about who they really are.