A couple of weeks ago, while watering my trees I accidentally flushed a Bell's Vireo off its nest, unaware the nest was there. I immediately backed away, it returned to the nest, and I roped off the area so that couldn't happen again. Since then either Mac or I have been monitoring the nest, hoping for a quick chance to check it for cowbird eggs. But the nest was never left alone for one second. One adult didn't leave until the other was there to slip into its place. I presume that's how they've adapted to the presence of cowbirds.
I'm in Alpine today, but Mac saw feeding activity in the nest today. Above photo courtesy of Mac. The nest is in a Chisos Rosewood (vaquelinia angustifolia).
I don't know the status of the new vireo nest above the walkway. Will post more on that soon.