After listening to a lot of birds on xenocanto I wonder if Cassin's Vireo would be a possibility. I've seen reports of a few of those moving through the area recently, and the general character of the song, at least, seems similar. Examples:

https://www.xeno-canto.org/131556

https://www.xeno-canto.org/128912

https://www.xeno-canto.org/308773

https://www.xeno-canto.org/378430

(Many more examples here: https://www.xeno-canto.org/species/Vireo-cassinii)

Among those who've responded privately to the email no one has committed to an ID, though a few have said they're pretty sure it's NOT a titmouse, at least. So that feels like progress, even if it ends up having to remain a mystery. :-)

Thanks again.

On Tue, Apr 3, 2018 at 12:03 PM, John Callender <callender.john@...> wrote:

I heard a bird singing in the canopy of a Coast Live Oak near Carpinteria Creek yesterday, and am not sure what it was. I wasn't able to see the singer, which appeared to be stationary for the several minutes I tried to see it. The song reminded me vaguely of Oak Titmouse, but I didn't hear any of the vocalizations I'm more familiar with that I would have expected to hear if that's what it was. It had a warbler/vireo character, and there are a lot of species in that group whose vocalizations I need to learn better, so maybe the ID will be obvious to someone?

The recording is here, if anyone is willing to give it a listen:

https://ebird.org/view/checklist/S44194850

Thanks.

John