This afternoon, I was birding at University of Guelph’s Arboretum. At one of the feeders, I heard a rather peculiar sounding black-capped chickadee. Here is a sound clip I took and uploaded to the Macaulay Library.
This is one of the calls of the complex vocal repertoire of the black-capped chickadees. This chicka-dee-dee call is usually made when they are alarmed. What I found interesting about this individual’s call was the dee-dee part. In the field, it sounded “not as full” to me, if that makes sense. As a reference, take a listen to this sound file of a black-capped chickadee (skip to roughly -24.000 seconds). Compared to the chickadee I heard, the dee-dee-dee sounds fuller and richer in this reference sound.
Recently, I have been getting into reading and analyzing bird sound spectrograms. This odd-sounding chickadee gave me a good opportunity to see if there was any difference in spectrograms between it and the calls I usually here, the “richer/fuller” calls.
The Macaulay Library website generates a spectrogram for any sound clip you upload. In my clip that I linked above, this is that gray-scale line plot that plays when you play the sound. However, I wanted to generate my own. Using the seewave library in R, I created two spectrograms: one for my odd chickadee, and one for the reference chickadee in that sound file I linked.
Here are the results. The first plot is my odd sounding chickadee, the second plot is the reference call.
Let’s first break down what we’re seeing here. The first two or three “curvy” lines that fall between 5-10 kHz of frequency is the chicka part of the call, and the rest of the horizontal lines that fall between 0-5 kHz frequency is the dee-dee-dee part of the song.
By inspecting both plots, I think you can see a clear difference in dee-dee part of the song, which is what I suspected. In my recording, there is only one clear spectral line present at ~4 kHz, with two very faint spectral lines appearing at ~2 kHz and ~5 kHz. Compare that to the reference file where there is essentially a stack of spectral lines between 2-5 kHz. This stack would create a richer, fuller sound which is what I usually hear in chickadee calls. Compare that to the one spectral line in my chickadee, and I think that’s a good explanation for the “emptiness” I heard in the dee-dees of that chickadee.
Black-capped chickadees are known to have rather complex vocalizations, variations of which can often be picked up in these spectrograms. This is just the first time I’ve heard a chickadee like this, and I thought it was super interesting to plot the sound. I’m not entirely sure if this can be chalked up to regular vocal variation, a young chickadee still learning its call, or something entirely different, but I’ll definitely be doing some research over the next few days to investigate this!