Around the trailer the most commonly heard song of a migrating or recently arrived bird is that of the Nashville Warbler. The song is two-parted, the first half a high, thin, up-and-down whistle, the last half a somewhat lower, slow trill. There's hardly a spot on this slope where you can't hear the birds, but they're not easy to see. When you do spot them, like most warblers, they're obsessively working along twigs and among leaves foraging for caterpillars and other small prey.
I never saw many Nashvilles back East. In both Kentucky and Mississippi the species only passes through during spring and fall migration, nesting in the northern states and Canada. I hadn't realized they'd be out here, much less so abundant.
If you thumb through your field guide's distribution maps for all the warblers you'll see that only Nashville Warblers have both eastern and western populations, while at the same time being absent from most of the mountainous West. As they migrate northward through Mexico their advancing wave splits into eastern and western factions and I just wonder why.
Nashville Warblers are the only North American warbler with a gray head, white eye ring, yellow throat, and no wingbars. You can read about them, see photos (click to enlarge), see distribution maps (on the left, BBS Map for summer map) and hear them at www.mbr-pwrc.usgs.gov/id/framlst/i6450id.html