Another Trip to Warbler Vista

Early this morning, Danielle and I went back to the Warbler Vista section of Balcones Canyonlands NWR and hiked the Cactus Rock Trail looking for warblers. We heard a half dozen Golden-cheeked Warblers, several along the lower part of the loop and the rest on the upper part and along the dirt road. We only got a glimpse of one. They are still singing the tweez tweez tweez tweez laaaazzy song. We also heard several Black and White Warblers singing a repeated wee-see wee-see wee-see pattern. Though badly back-lit, we did get a photograph of one of them.

Black and White Warbler
Canon EF 100-400mm f/4.5-5.6L - ISO-800, 400mm, f/6.3, 1/250s (EC+0.3, FEC -2-2/3)

There were several other prominent songs we heard including that of a Black-crested Titmouse. We did not recognize any of the others.

We also passed by the Golden-cheeked Warbler nest that I reported on two weeks ago. During the quarter hour we look, we heard no nearby song and no birds were apparent in the nest. This leaves me wondering what I was seeing last time. A Texas Parks and Wildlife article on the species indicates that nesting occurs in April, eggs are incubated for 12 days and fledging occurs in about 8-12 days. Thereafter, the chick separate and follow one of the parent for up to 30 days. I can see three possibilities:

1. The female was preparing her nest but abandoned it or the nest was pillaged. This would be pretty depressing and was my first thought.
2. The bird I saw being fed was not the adult female but a fledgling from a nesting early in April. This seems unlikely as the both birds I saw looked like adults. 
3. The eggs were being incubated or had just hatched on my last visit and the chicks have since fledged. The nest is no longer being used and parents and fledglings would be foraging elsewhere. There would have been just enough time for this.