One of the highlights were the excellent views of this brilliant Slaty Vireo before the sun rose over the hillside. The psychotic white eyes of this bird are reminiscent of the White-eyed Vireo, but the chartreuse and gray color scheme is striking once it comes into the open. 
Among the ruins a Northern Beardless-Tyrannulet put on a show, but remained silent.
Other highlights included Ocellated Thrasher (distant views), Dusky Hummingbird, Pileated Flycatcher, and of course the spectacular ruins. 
Eric Antonio Martinez, our guide (see previous post for contact info for Eric) provided an excellent overview to the site, the times, and the 30,000 Zapotecs that resided there at one time. 
Robert was savvy and realized that only former residents of the site were allowed to sell handicrafts inside the site, and that these works were likely to be (much) better quality than those available in the parking lot. I wish I'd spent more time shopping, but I'm always more focused on birds in the cool hours when they are most active.
Later on we stopped at the famous Tule Tree or Big Tree, a huge bald cypress in the town of Santa Maria de Tule, Oaxaca. I can't begin to imagine the amount of biomass in this one single tree. 
There's no way to convey the huge size of this tree with a camera, the perspective is too easily lost. Birds aside, it's worth a visit if you're in Oaxaca.
We spent the rest of the afternoon walking along Highway 175 in lowland thornscrub, finding a pair of Oaxaca Sparrows, a stunning Elegant Euphonia and a Dwarf Vireo, which put on a show for all of us minutes before the rains came.
