On 12 January 2009, my friend Andrew Spencer recorded an unseen creature on Chews Ridge in Monterey County, California:
To my ear this sounds like a Northern Pygmy-Owl (sensu stricto: Glaucidium gnoma californicum), and the spectrogram shows many of the characteristics of that species. The note shape is pretty classic, with a sharp initial upslur and terminal downslur, and an overall barely downslurred trend to the rest of the note. Almost all of the energy is concentrated in the fundamental, but a couple of faint harmonics are visible, which is standard for pygmy-owls.
But a few things about this recording are strange:
- The notes are quite short, about half the length of the average Northern Pygmy-Owl note;
- The rate of the series is quite fast (on average about 1 note every 0.66 sec), which is more than twice as fast as you’d expect from pygmy-owls from California;
- The pitch of the notes is just a little high, about 1.5 kHz, while most Northern Pygmy-Owl notes fall just above 1.0 kHz;
- Oddly, Andrew reports that the sound was coming not from a tree or bush, but from somewhere on the ground. It’s unlikely that Andrew misjudged the origin of the call: he was aiming at it with a parabolic dish, and if the source of the sound hadn’t been close to the focus of the parabola, most likely the harmonic would be absent from the spectrogram and the echo would be louder in relation to the original sound.
Because the sound came from the ground, Andrew surmised that he might have recorded some kind of mammal. But what kind of mammal could sound so remarkably similar to a pygmy-owl? If there is a mammal in California that sounds like this, then I want to know about it.
I did manage to find a recording that matched Andrew’s: Doug Von Gausig made this recording in almost the same place: along the Carmel Valley Road just east of Carmel, California, on 24 March 1999. In an email, Doug told me his pygmy-owl was unseen, but positioned high within the trees in a dense gallery forest.
The bird on Doug’s recording is even higher-pitched and faster than the one on Andrew’s. Together, these two recordings represent quite a departure from what I’ve come to think of as the “typical” song of californicum. Xeno-Canto, the Macaulay Library and the Borror Lab, between them, have nine recordings of the primary song of Northern Pygmy-Owl, from California, Oregon, Montana, Colorado and Utah. None of the birds in these recordings quite match the Spencer/Von Gausig birds in note length or pitch, and most strikingly, none of them come close in rate: the Borror bird from Utah and Jason Beason’s Colorado bird average about one note every 1.5 sec, while the rest, including the Montana bird, average a note every 2.0 sec or more. At the moment, I’m still a little skeptical that “interior” Northern Pygmy-Owls sing significantly faster than “coastal” Northern Pygmy-Owls on average, but I have long agreed that “Mountain” Pygmy-Owls (Glaucidium gnoma gnoma), which breed from southern Arizona south through Mexico, sing very differently from californicum and probably deserve species status. Here’s their standard song:
In addition to the typical song with the irregular rhythm, “Mountain” Pygmy-Owls apparently sometimes give a faster, stricter song that is very similar to the song of the Northern Saw-Whet Owl (so similar, in fact, that I suspect the two may represent a vastly underrated ID problem). See the Xeno-Canto forum discussions (here and here) of Allen Chartier’s seven cuts of fast Mountain Pygmy-Owl song from Oaxaca. I was particularly struck by Rich Hoyer’s understanding of a stepwise slowing trend in pygmy-owl song rates as you move counterclockwise from Mexico to Colorado to California to Baja California Sur. Up to a point, that jives with the information I have, but what to make of the two birds from Monterey County that sing at a rate of about 80 notes/minute? Are they representatives of an anomalous local dialect? Or of a different type of vocalization than the primary song? Are they not even pygmy-owls at all?