Perhaps a flycatcher or vireo. Identotron suggests least flycather but also includes Hutton's vireo on the list of possiblities. Unfortunately, I could not get a better view of this bird.

wide view shots of the tree show scattering of junipers in the background.

Dove down into the nearby undergrowth several times chasing sparrows and, at one point, a rabbit

3-5 in total