Adapted from Jim Conrad's online book A Birding Trip through Mexico, This excerpt from "Hot & Steamy at Témoris Station"
in western Chihuahua state

The Solitary Vireo's taxonomy is complex. Some authors separate the Solitary Vireo into the Blue-headed, Cassins and Plumbeous Vireos. Judging from distribution maps in Howell & Webb's field guide, this could have been either the Cassin's or Plumbeous Vireo.
In the late afternoon I sit on a boulder next to the fig's smooth, slate-gray trunk. Not three arm-lengths away, a Solitary Vireo alights on one of the tree's lower branches, assumes a comfortable-looking perching position, and cocks his head slightly. He holds his head sideways so that his left eye, highlighted with a thin eye-ring, stares exactly at me. He makes not a sound and twitches not a feather. In such a manner this bird perches for a solid hour, absolutely unmoving, always with that left eye riveted right on me.

Though it would be interesting to see just how long this bird can look at me, after an hour I want to move to another rock. The moment I stand up the vireo takes flight. He lands in the top of a nearby tree and for a full minute goes into a paroxysm of alternately hopping and flitting about, and ruffling his feathers -- giving a clear impression of "letting off steam" after his period of intense observation and inactivity. At the minute's end, he flies away. I have never seen a bird behave like this.

At dusk, however, he returns to another nearby perch and continues his earlier intense watchfulness until darkness enshrouds all, and I feel my way into the tent.

Awaiting sleep, I can't shake the feeling that the vireo's behavior is downright spooky. I wonder what a superstitious person would make of the visit? Here in the shadowy belly of an almost supernatural-looking canyon, I wonder what omens, what kinds of vision, what spirits or apparitions a mind could attribute to this little bird's behavior if one just allowed the mind to wander... ?