One spring morning, scanning the treetops in Central Park, I spotted a smear of ultramarine against the paler blue of the sky. I raised my binoculars, tweaked the focus, and there it was: an Indigo Bunting. I stood transfixed. While it was a treat to spot this bird in Manhattan, seeing an Indigo Bunting isn’t exactly difficult; they’re among the most common songbirds in the East. It wasn’t a lifer for any of the folks I was birding with. And yet, on a morning when we saw grosbeaks, orioles, and an embarrassment of spellbinding warblers, the consensus held that a highlight of the morning—maybe the highlight—was that brilliant bunting. On the walk home I thought with envy of the Southeastern birders who regularly encounter absurdly beautiful Painted Buntings. Then I envisioned the more subdued but no less lovely palette of the Lazuli Bunting that graces the West. And jeez, could you imagine hiking some desert Southwest canyon and stumbling across a Varied Bunting in...